WO2025072217A1

WO2025072217A1 - Audio playback devices with auxiliary magnetic elements

Info

Publication number: WO2025072217A1
Application number: PCT/US2024/048236
Authority: WO
Inventors: Naphur VAN APELDOORN; Timothy Ruben SCHEEK; Andrei KOZHEVNIKOV
Original assignee: Sonos Inc
Current assignee: Sonos Inc
Priority date: 2023-09-27
Filing date: 2024-09-24
Publication date: 2025-04-03
Anticipated expiration: 2026-03-27

Abstract

An audio playback device includes a membrane configured to move inward and outward along an excursion axis and a voice coil operably coupled to the membrane that is configured to move axially inward and outward over an excursion range. The device further includes a negative-stiffness assembly including a stationary first magnetic element aligned along a drive axis parallel to the excursion axis and a plurality of moveable second magnetic elements arranged circumferentially around the drive axis and coupled to the voice coil. The plurality of moveable second magnetic elements create a magnetic force that at least partially cancels a mechanical force on the membrane as it moves along the excursion axis.

Description

AUDIO PLAYBACK DEVICES WITH AUXILIARY MAGNETIC ELEMENTS

CROSS-REFERENCE IN RELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Patent Application No. 63/585.789, filed September 27, 2023, which is incorporated herein by reference in its entirety'.

FIELD OF THE DISCLOSURE

[0002] The present disclosure is related to consumer goods and, more particularly, to methods, systems, products, features, sendees, and other elements directed to media playback or some aspect thereof.

BACKGROUND

[0003] Options for accessing and listening to digital audio in an out-loud setting were limited until in 2002, when SONOS, Inc. began development of anew type of playback system. Sonos then filed one of its first patent applications in 2003, entitled “Method for Synchronizing Audio Playback between Multiple Networked Devices,’' and began offering its first media playback systems for sale in 2005. The Sonos Wireless Home Sound System enables people to experience music from many sources via one or more networked playback devices. Through a software control application installed on a controller (e.g., smartphone, tablet, computer, voice input device), one can play what she wants in any room having a networked playback device. Media content (e.g., songs, podcasts, video sound) can be streamed to playback devices such that each room with a playback device can play back corresponding different media content. In addition, rooms can be grouped together for synchronous playback of the same media content, and/or the same media content can be heard in all rooms synchronously.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Features, examples, and advantages of the presently disclosed technology may be better understood with regard to the following description, appended claims, and accompanying drawings, as listed below. A person skilled in the relevant art will understand that the features shown in the drawings are for purposes of illustrations, and variations, including different and/or additional features and arrangements thereof, are possible.

[0005] Figure 1A is a partial cutaway view of an environment having a media playback system configured in accordance with examples of the disclosed technology.

[0006] Figure IB is a schematic diagram of the media playback system of Figure 1 A and one or more networks.

[0007] Figure 1C is a block diagram of a playback device. [0008] Figure ID is a block diagram of a playback device.

[0009] Figure IE is a block diagram of a network microphone device.

[0010] Figure IF is a block diagram of a network microphone device.

[0011] Figure 1G is a block diagram of a playback device.

[0012] Figure 1H is a partially schematic diagram of a control device.

[0013] Figure 2A is a block diagram of a playback device in accordance with examples of the disclosed technology.

[0014] Figure 2B is a plan view of an audio transducer of the playback device shown in Figure 2 A.

[0015] Figure 2C is a side cross-sectional view of the audio transducer shown in Figure 2B in a rest position.

[0016] Figure 2D is a side cross-sectional view of the audio transducer shown in Figure 2B in a position of inward excursion.

[0017] Figure 3A is a schematic cross-sectional view of an example drive unit for an audio transducer in accordance with examples of the disclosed technology.

[0018] Figure 3B is a side perspective view of the drive unit shown in Figure 3A.

[0019] Figure 4A is a schematic cross-sectional view of another example drive unit for an audio transducer in accordance with examples of the disclosed technology⁷.

[0020] Figure 4B is a side perspective view of the drive unit shown in Figure 4A.

[0021] Figure 5A is a schematic cross-sectional view of another example drive unit for an audio transducer in accordance with examples of the disclosed technology.

[0022] Figure 5B is a top side perspective view⁷ of the drive unit shown in Figure 5A.

[0023] Figure 6A is a schematic cross-sectional view- of another example drive unit for an audio transducer in accordance with examples of the disclosed technology.

[0024] Figure 6B is a side perspective view of the drive unit shown in Figure 6A.

[0025] Figures 7A-7G illustrate example magnetic elements for use in a drive unit for an audio transducer in accordance with examples of the disclosed technology⁷.

[0026] Figure 8 illustrates an example auxiliary magnetic element support for use in a drive unit for an audio transducer in accordance with examples of the disclosed technology⁷.

[0027] The drawings are for the purpose of illustrating example examples, but those of ordinary⁷ skill in the art will understand that the technology⁷ disclosed herein is not limited to the arrangements and/or instrumentality shown in the drawings. DETAILED DESCRIPTION

I. Overview

[0028] Electroacoustic audio transducers typically include a membrane, a suspension supporting the membrane, and a drive unit configured to move the membrane inward and outward in an oscillating fashion. The suspension can maintain the proper structural orientation of the membrane, but also contributes stiffness to movement of the membrane (e.g., by providing some resistance to axial displacement from a rest position). Additional stiffness due to air pressure arises for audio transducers that are mounted in an enclosure, such as transducers configured to output mid- and low-frequency audio. While mounting such transducers in an enclosure can improve acoustic output, the additional stiffness due to air pressure increases the total stiffness that needs to be overcome by the drive unit to move the membrane. The greater the overall stiffness, the more power is required to move the membrane inward and outward via the drive unit. As such, it can be beneficial to reduce the overall stiffness of an audio transducer while maintaining the structural benefits of the suspension components and the acoustic benefits of an enclosure.

[0029] Aspects of the present technology relate to the use of auxiliary magnetic elements that are configured to contribute a negative stiffness to movement of the membrane over at least a portion of its range of operation. In particular, an example drive unit includes a stationary portion that is fixed relative to a frame and a moveable portion coupled to the membrane. The moveable portion is configured to move axially inward and outward along a drive axis relative to the stationary portion. The stationary portion can include, for instance, a primary magnetic element (e.g., a magnet, stack of magnets, etc.) that provides a primary spatial magnetic field. The moveable portion of the drive unit can include a voice coil configured to move axially inward and outward along a drive axis in the presence of the primary spatial magnetic field in response to electric current passing through the voice coil. The moveable portion can further include one or more auxiliary magnetic elements that are coupled to the voice coil such that the voice coil and auxiliary magnetic element(s) move together. These auxiliary magnetic element(s) can be positioned and configured such that, when the voice coil is at a neutral position (e.g., the transducer is at rest), there is little or no magnetic force urging the moveable portion of the drive unit away from the rest position. As the moveable portion of the drive unit moves axially away from the rest position (i.e., axially inward or outward along a drive axis due in response to current passing through the voice coil), the magnetic interactions between the primary magnetic element(s) and the auxiliary magnetic element(s) amplifies this motion over at least a portion of the excursion range, thereby urging both the voice coil and the auxiliary magnetic element(s) further away from the rest position. This amplification contributes a negative stiffness to movement of the voice coil and membrane along the excursion axis, thereby increasing the transducer efficiency.

[0030] In some implementations, the auxiliary magnetic element(s) include one or more rings extending circumferentially around the drive axis, for instance extending circumferentially around the primary magnetic element(s). Because the auxiliary magnetic element(s) move along with the voice coil, it is beneficial to reduce the weight of the auxiliary magnetic element(s) to the extent possible. While thin magnetic rings can provide the benefits of increased transducer efficiency, in practice it can be difficult to reliably manufacture thin rings of the appropriate dimensions, and the resulting rings may be fragile and susceptible to deformation during assembly and during operation of the device. Accordingly, in some implementations of the present technology⁷, the auxiliary⁷ magnetic element(s) can take the form of a plurality of discrete magnetic bodies arranged circumferentially around the drive axis. In one example, 12 small rod-shaped magnets may be arranged around the drive axis such that the magnets are evenly spaced apart from one another along the circumferential direction. The negative-stiffness contribution of these discrete magnets may be similar to that of a corresponding solid annular ring. However, the discrete magnets may be more easily manufacturable and less susceptible to warping or deformation during operation of the transducer. In some instances, moreover, the arrangement of particular magnetic bodies can vary to achieve more complex magnetic interactions, providing for more fine-tuned control of the spatial magnetic field resulting from the combination of individual magnetic bodies, and therefore more fine-tuned control of the negative-stiffness curve due to the auxiliary magnetic element(s). For instance, a first subset of the magnetic bodies may be arranged along a first plane that is offset from the voice coil by a first distance, and a second subset of the magnetic bodies may be arranged along a second plane that is offset from the voice coil by a second distance from the voice coil. Moreover, the shape, size, and magnetic orientation of the individual magnetic bodies may vary, which also can affect the spatial distribution of the resulting auxiliary magnetic field.

[0031] In operation, the auxiliary⁷ magnetic elements interact with the primary magnetic element(s) such that, as voice coil moves along the drive axis, the combined forces generated by the primary magnetic element(s) and the auxiliary magnetic element(s) amplify the voice coil movement. Thus, the present technology provides an energy efficient and improved linear drive unit by decreasing the stiffness over at least a portion of the excursion range of the drive unit. This stiffness reduction thereby effectively decreases the power needed for the drive unit to move inward and outward along the excursion range.

[0032] In the Figures, identical reference numbers identify generally similar, and/or identical, elements. To facilitate the discussion of any particular element, the most significant digit or digits of a reference number refers to the Figure in which that element is first introduced. For example, element 110a is first introduced and discussed with reference to Figure 1 A. Many of the details, dimensions, angles and other features show n in the Figures are merely illustrative of particular examples of the disclosed technology. Accordingly, other examples can have other details, dimensions, angles and features without departing from the spirit or scope of the disclosure. In addition, those of ordinary skill in the art will appreciate that further examples of the various disclosed technologies can be practiced without several of the details described below.

II. Suitable Operating Environment

[0033] Figure 1A is a partial cutaway view of a media playback system 100 distributed in an environment 101 (e.g., a house). The media playback system 100 comprises one or more playback devices 110 (identified individually as playback devices HOa-n), one or more network microphone devices (“NMDs”), 120 (identified individually as NMDs 120a-c), and one or more control devices 130 (identified individually as control devices 130a and 130b).

[0034] As used herein the term “playback device” can generally refer to a network device configured to receive, process, and output data of a media playback system. For example, a playback device can be a network device that receives and processes audio, visual content, or both audio and visual content. In some examples, a playback device includes one or more transducers or speakers powered by one or more amplifiers. In other examples, however, a playback device includes one of (or neither of) the speaker and the amplifier. For instance, a playback device can comprise one or more amplifiers configured to drive one or more speakers external to the playback device via a corresponding wire or cable. In some embodiments, a playback device includes a display component (e.g., a screen, projector, etc.) or is otherwise communicatively coupled to a display component for the playback of visual content.

[0035] Moreover, as used herein the term NMD (i.e., a “network microphone device”) can generally refer to a network device that is configured for audio detection. In some examples, an NMD is a stand-alone device configured primarily for audio detection. In other examples, an NMD is incorporated into a playback device (or vice versa). [0036] The term "control device'’ can generally refer to a network device configured to perform functions relevant to facilitating user access, control, and/or configuration of the media playback system 100.

[0037] Each of the playback devices 110 is configured to receive audio signals or data from one or more media sources (e.g., one or more remote servers, one or more local devices) and play back the received audio signals or data as sound. The one or more NMDs 120 are configured to receive spoken word commands, and the one or more control devices 130 are configured to receive user input. In response to the received spoken word commands and/or user input, the media playback system 100 can play back audio via one or more of the playback devices 110. In certain examples, the playback devices 110 are configured to commence playback of media content in response to a trigger. For instance, one or more of the playback devices 110 can be configured to play back a morning playlist upon detection of an associated trigger condition (e.g., presence of a user in a kitchen, detection of a coffee machine operation). In some examples, for instance, the media playback system 100 is configured to play back audio from a first playback device (e.g., the playback device 110a) in synchrony with a second playback device (e.g., the playback device 110b). Interactions between the playback devices 110, NMDs 120, and/or control devices 130 of the media playback system 100 configured in accordance with the various examples of the disclosure are described in greater detail below.

[0038] In the illustrated example of Figure 1 A, the environment 101 comprises a household having several rooms, spaces, and/or playback zones, including (clockwise from upper left) a master bathroom 101a, a master bedroom 101b, a second bedroom 101c, a family room or den lOld, an office lOle, a living room lOlf, a dining room 101g, a kitchen lOlh, and an outdoor patio lOli. While certain examples and examples are described below in the context of a home environment, the technologies described herein may be implemented in other types of environments. In some examples, for instance, the media playback system 100 can be implemented in one or more commercial settings (e.g., a restaurant, mall, airport, hotel, a retail or other store), one or more vehicles (e.g., a sports utility vehicle, bus, car, a ship, a boat, an airplane), multiple environments (e.g., a combination of home and vehicle environments), and/or another suitable environment where multi -zone audio may be desirable.

[0039] The media playback system 100 can comprise one or more playback zones, some of which may correspond to the rooms in the environment 101. The media playback system 100 can be established with one or more playback zones, after which additional zones may be added, or removed to form, for example, the configuration shown in Figure 1 A. Each zone may be given a name according to a different room or space such as the office lOle, master bathroom 101a, master bedroom 101b, the second bedroom 101c, kitchen lOlh. dining room 101g, living room lOlf, and/or the balcony lOli. In some examples, a single playback zone may include multiple rooms or spaces. In certain examples, a single room or space may include multiple playback zones.

[0040] In the illustrated example of Figure 1A, the master bathroom 101a, the second bedroom 101c, the office 101 e, the living room 101 f, the dining room 101g, the kitchen lOlh, and the outdoor patio lOli each include one playback device 110, and the master bedroom 101b and the den 101 d include a plurality⁷ of playback devices 110. In the master bedroom 101b, the playback devices 1101 and 11 Om may be configured, for example, to play back audio content in synchrony as individual ones of playback devices 110. as a bonded playback zone, as a consolidated playback device, and/or any combination thereof. Similarly, in the den 101 d, the playback devices HOh-j can be configured, for instance, to play back audio content in synchrony as individual ones of playback devices 110, as one or more bonded playback devices, and/or as one or more consolidated playback devices. Additional details regarding bonded and consolidated playback devices are described below with respect to Figures IB and IE.

[0041] In some examples, one or more of the playback zones in the environment 101 may each be playing different audio content. For instance, a user may be grilling on the patio lOli and listening to hip hop music being played by the playback device 110c while another user is preparing food in the kitchen lOlh and listening to classical music played by the playback device 110b. In another example, a playback zone may play the same audio content in synchrony with another playback zone. For instance, the user may be in the office lOle listening to the playback device 1 lOf playing back the same hip hop music being played back by playback device 110c on the patio lOli. In some examples, the playback devices 110c and 11 Of play back the hip hop music in synchrony such that the user perceives that the audio content is being played seamlessly (or at least substantially seamlessly) while moving between different playback zones. Additional details regarding audio playback synchronization among playback devices and/or zones can be found, for example, in U.S. PatentNo. 8,234,395 entitled, “System and method for synchronizing operations among a plurality of independently clocked digital data processing devices,” which is incorporated herein by reference in its entirety. a. Suitable Media Playback System

[0042] Figure IB is a schematic diagram of the media playback system 100 and a cloud network 102. For ease of illustration, certain devices of the media playback system 100 and the cloud network 102 are omitted from Figure 1 B. One or more communication links 103 (referred to hereinafter as ‘‘the links 103”) communicatively couple the media playback system 100 and the cloud network 102.

[0043] The links 103 can comprise, for example, one or more wired networks, one or more wireless networks, one or more wide area networks (WAN), one or more local area networks (LAN), one or more personal area networks (PAN), one or more telecommunication networks (e.g., one or more Global System for Mobiles (GSM) networks, Code Division Multiple Access (CDMA) networks, Long-Term Evolution (LTE) networks. 5G communication network networks, and/or other suitable data transmission protocol networks), etc. The cloud netw ork 102 is configured to deliver media content (e.g., audio content, video content, photographs, social media content) to the media playback system 100 in response to a request transmitted from the media playback system 100 via the links 103. In some examples, the cloud network 102 is further configured to receive data (e.g. voice input data) from the media playback system 100 and correspondingly transmit commands and/or media content to the media playback system 100.

[0044] The cloud network 102 comprises computing devices 106 (identified separately as a first computing device 106a, a second computing device 106b. and a third computing device 106c). The computing devices 106 can comprise individual computers or servers, such as, for example, a media streaming service server storing audio and/or other media content, a voice serv ice server, a social media server, a media playback system control server, etc. In some examples, one or more of the computing devices 106 comprise modules of a single computer or server. In certain examples, one or more of the computing devices 106 comprise one or more modules, computers, and/or servers. Moreover, while the cloud netw ork 102 is described above in the context of a single cloud network, in some examples the cloud netw ork 102 comprises a plurality of cloud networks comprising communicatively coupled computing devices. Furthermore, while the cloud network 102 is shown in Figure IB as having three of the computing devices 106, in some examples, the cloud netw ork 102 comprises few er (or more than) three computing devices 106.

[0045] The media playback system 100 is configured to receive media content from the networks 102 via the links 103. The received media content can comprise, for example, a Uniform Resource Identifier (URI) and/or a Uniform Resource Locator (URL). For instance, in some examples, the media playback system 100 can stream, download, or otherwise obtain data from a URI or a URL corresponding to the received media content. A network 104 communicatively couples the links 103 and at least a portion of the devices (e.g., one or more of the playback devices 110, NMDs 120, and/or control devices 130) of the media playback system 100. The network 104 can include, for example, a wireless network (e.g., a WiFi network, a Bluetooth, a Z-Wave network, a ZigBee, and/or other suitable wireless communication protocol network) and/or a wired network (e.g., a network comprising Ethernet, Universal Serial Bus (USB), and/or another suitable wired communication). As those of ordinary skill in the art will appreciate, as used herein, “WiFi” can refer to several different communication protocols including, for example, Institute of Electrical and Electronics Engineers (IEEE) 802.11a, 802.1 1b, 802.11g, 802.11n, 802.1 lac, 802.11ac, 802.11ad, 802.11af, 802. 11 ah, 802.1 lai, 802.11aj, 802.11aq, 802.1 lax, 802. Hay, 802.15, etc. transmitted at 2.4 Gigahertz (GHz), 5 GHz, and/or another suitable frequency.

[0046] In some examples, the network 104 comprises a dedicated communication network that the media playback system 100 uses to transmit messages between individual devices and/or to transmit media content to and from media content sources (e.g., one or more of the computing devices 106). In certain examples, the network 104 is configured to be accessible only to devices in the media playback system 100, thereby reducing interference and competition with other household devices. In other examples, however, the network 104 comprises an existing household communication network (e.g., a household WiFi network). In some examples, the links 103 and the netw ork 104 comprise one or more of the same netw orks. In some examples, for instance, the links 103 and the network 104 comprise a telecommunication network (e.g., an LTE network, a 5G network). Moreover, in some examples, the media playback system 100 is implemented without the network 104, and devices comprising the media playback system 100 can communicate with each other, for example, via one or more direct connections, PANs, telecommunication networks, and/or other suitable communication links.

[0047] In some examples, audio content sources may be regularly added or removed from the media playback system 100. In some examples, for instance, the media playback system 100 performs an indexing of media items w hen one or more media content sources are updated, added to. and/or removed from the media playback system 100. The media playback system 100 can scan identifiable media items in some or all folders and/or directories accessible to the playback devices 110, and generate or update a media content database comprising metadata (e.g.. title, artist, album, track length) and other associated information (e.g., URIs. URLs) for each identifiable media item found. In some examples, for instance, the media content database is stored on one or more of the playback devices 110, network microphone devices 120, and/or control devices 130.

[0048] In the illustrated example of Figure IB, the playback devices 1101 and 110m comprise a group 107a. The playback devices 1 101 and 1 10m can be positioned in different rooms in a household and be grouped together in the group 107a on a temporary or permanent basis based on user input received at the control device 130a and/or another control device 130 in the media playback system 100. When arranged in the group 107a, the playback devices 1101 and 110m can be configured to play back the same or similar audio content in synchrony from one or more audio content sources. In certain examples, for instance, the group 107a comprises a bonded zone in which the playback devices 1101 and 110m comprise left audio and right audio channels, respectively, of multi-channel audio content, thereby producing or enhancing a stereo effect of the audio content. In some examples, the group 107a includes additional playback devices 1 10. In other examples, however, the media playback system 100 omits the group 107a and/or other grouped arrangements of the playback devices 110.

[0049] The media playback system 100 includes the NMDs 120a and 120d, each comprising one or more microphones configured to receive voice utterances from a user. In the illustrated example of Figure IB. the NMD 120a is a standalone device and the NMD 120d is integrated into the playback device 11 On. The NMD 120a, for example, is configured to receive voice input 121 from a user 123. In some examples, the NMD 120a transmits data associated with the received voice input 121 to a voice assistant service (VAS) configured to (i) process the received voice input data and (ii) transmit a corresponding command to the media playback system 100. In some examples, for instance, the computing device 106c comprises one or more modules and/or servers of a VAS (e.g., a VAS operated by one or more of SONOS®, AMAZON®, GOOGLE® APPLE®, MICROSOFT®). The computing device 106c can receive the voice input data from the NMD 120a via the network 104 and the links 103. In response to receiving the voice input data, the computing device 106c processes the voice input data (i.e., ‘'Play Hey Jude by The Beatles’’), and determines that the processed voice input includes a command to play a song (e.g., “Hey Jude”). The computing device 106c accordingly transmits commands to the media playback system 100 to play back “Hey Jude” by the Beatles from a suitable media service (e.g., via one or more of the computing devices 106) on one or more of the playback devices 110. b. Suitable Playback Devices

[0050] Figure 1C is a block diagram of the playback device 110a comprising an input/output 111. The input/output 111 can include an analog I/O I l la (e.g., one or more wires, cables, and/or other suitable communication links configured to carry analog signals) and/or a digital I/O 111b (e.g., one or more wires, cables, or other suitable communication links configured to carry digital signals). In some examples, the analog I/O I l la is an audio line-in input connection comprising, for example, an auto-detecting 3.5mm audio line-in connection. In some examples, the digital I/O 111b comprises a Sony /Philips Digital Interface Format (S/PDIF) communication interface and/or cable and/or a Toshiba Link (TOSLINK) cable. In some examples, the digital I/O 111b comprises a High-Definition Multimedia Interface (HDMI) interface and/or cable. In some examples, the digital I/O 111b includes one or more wireless communication links comprising, for example, a radio frequency (RF), infrared, WiFi, Bluetooth, or another suitable communication protocol. In certain examples, the analog I/O 11 la and the digital 111b comprise interfaces (e.g., ports, plugs, jacks) configured to receive connectors of cables transmitting analog and digital signals, respectively, without necessarily including cables.

[0051] As shown in Figure 1C, the playback device 110a can also include an analog source component 1 16. In various examples, the analog source component 116 can be integrated into the same housing or operably coupled to other components while itself positioned in a separate housing or enclosure. The analog source component 116 can be, for example, any suitable component or set of components configured to facilitate playback of analog media content such as vinyl records, magnetic tape cassettes, or other such analog content. In some examples, the analog source component 116 can take the form of a turntable-style record player (e.g., including a rotatable platter and a tonearm carrying a cartridge and needle). As described in more detail elsewhere herein, the analog source component 116 can be used to enable playback of physical, analog media content (e.g., vinyl LPs) while also providing additional functionality as compared to conventional analog playback devices.

[0052] Additionally, the playback device 110a can receive media content (e.g., audio content comprising music and/or other sounds) from a local audio source 105 via the input/output 111 (e.g., a cable, a wire, a PAN, a Bluetooth connection, an ad hoc wired or wireless communication network, and/or another suitable communication link). The local audio source 105 can comprise, for example, a mobile device (e.g., a smartphone, a tablet, alaptop computer) or another suitable audio component (e.g., a television, a desktop computer, an amplifier, a phonograph, a Blu-ray player, a memory storing digital media files). In some examples, the local audio source 105 includes local music libraries on a smartphone, a computer, a networked- attached storage (NAS), and/or another suitable device configured to store media files. In certain examples, one or more of the playback devices 110, NMDs 120, and/or control devices 130 comprise the local audio source 105. In other examples, however, the media playback system omits the local audio source 105 altogether. In some examples, the playback device 110a does not include an input/ output 111 and receives all audio content via the network 104.

[0053] The playback device 110a further comprises electronics 112, a user interface 113 (e.g., one or more buttons, knobs, dials, touch-sensitive surfaces, displays, touchscreens), and one or more transducers 114 (referred to hereinafter as "the transducers 114”). The electronics 112 is configured to receive audio from an audio source (e.g., the local audio source 105) via the input/output 111. one or more of the computing devices 106a-c via the network 104 (Figure IB)), amplify the received audio, and output the amplified audio for playback via one or more of the transducers 114. In some examples, the playback device 110a optionally includes one or more microphones 115 (e.g., a single microphone, a plurality' of microphones, a microphone array) (hereinafter referred to as “the microphones 115”). In certain examples, for instance, the playback device 110a having one or more of the optional microphones 115 can operate as an NMD configured to receive voice input from a user and correspondingly perform one or more operations based on the received voice input.

[0054] In the illustrated example of Figure 1C, the electronics 112 comprise one or more processors 112a (referred to hereinafter as “the processors 112a”), memory 112b. software components 112c, a network interface 112d, one or more audio processing components 112g (referred to hereinafter as “the audio components 112g”), one or more audio amplifiers 112h (referred to hereinafter as “the amplifiers 112h”), and power 112i (e.g., one or more power supplies, power cables, power receptacles, batteries, induction coils, Power-over Ethernet (POE) interfaces, and/or other suitable sources of electric power). In some examples, the electronics 112 optionally include one or more other components 112j (e.g., one or more sensors, video displays, touchscreens, battery' charging bases).

[0055] The processors 112a can comprise clock-driven computing component(s) configured to process data, and the memory 112b can comprise a computer-readable medium (e.g., a tangible, non-transitory computer-readable medium, data storage loaded with one or more of the software components 112c) configured to store instructions for performing various operations and/or functions. The processors 112a are configured to execute the instructions stored on the memory 112b to perform one or more of the operations. The operations can include, for example, causing the playback device 110a to retrieve audio data from an audio source (e.g., one or more of the computing devices 106a-c (Figure IB)), and/or another one of the playback devices 110. In some examples, the operations further include causing the playback device 110a to send audio data to another one of the playback devices 110a and/or another device (e.g., one of the NMDs 120). Certain examples include operations causing the playback device 110a to pair with another of the one or more playback devices 110 to enable a multi-channel audio environment (e.g., a stereo pair, a bonded zone).

[0056] The processors 112a can be further configured to perform operations causing the playback device 110a to synchronize playback of audio content with another of the one or more playback devices 110. As those of ordinary skill in the art will appreciate, during synchronous playback of audio content on a plurality’ of playback devices, a listener will preferably be unable to perceive time-delay differences between playback of the audio content by the playback device 110a and the other one or more other playback devices 110. Additional details regarding audio playback synchronization among playback devices can be found, for example, in U.S. Patent No. 8,234,395, which was incorporated by reference above.

[0057] In some examples, the memory 112b is further configured to store data associated with the playback device 110a, such as one or more zones and/or zone groups of which the playback device 110a is a member, audio sources accessible to the playback device 110a, and/or a playback queue that the playback device 110a (and/or another of the one or more playback devices) can be associated with. The stored data can comprise one or more state variables that are periodically updated and used to describe a state of the playback device 110a. The memory⁷ 112b can also include data associated with a state of one or more of the other devices (e.g., the playback devices 110, NMDs 120, control devices 130) of the media playback system 100. In some examples, for instance, the state data is shared during predetermined intervals of time (e.g., every 5 seconds, every 10 seconds, every 60 seconds) among at least a portion of the devices of the media playback system 100, so that one or more of the devices have the most recent data associated with the media playback system 100.

[0058] The network interface 112d is configured to facilitate a transmission of data between the playback device 110a and one or more other devices on a data network such as. for example. the links 103 and/or the network 104 (Figure IB). The network interface 112d is configured to transmit and receive data corresponding to media content (e.g., audio content, video content, text, photographs) and other signals (e.g., non-transitory signals) comprising digital packet data including an Internet Protocol (IP)-based source address and/or an IP-based destination address. The network interface 112d can parse the digital packet data such that the electronics 112 properly receives and processes the data destined for the playback device 110a.

[0059] In the illustrated example of Figure 1C, the network interface 112d comprises one or more wireless interfaces 112e (referred to hereinafter as “the wireless interface 112e”). The wireless interface 112e (e.g., a suitable interface comprising one or more antennae) can be configured to wirelessly communicate with one or more other devices (e.g.. one or more of the other playback devices 110, NMDs 120. and/or control devices 130) that are communicatively coupled to the network 104 (Figure IB) in accordance with a suitable wireless communication protocol (e.g., WiFi, Bluetooth, LTE). In some examples, the network interface 112d optionally includes a wired interface 112f (e.g., an interface or receptacle configured to receive a network cable such as an Ethernet, a USB-A, USB-C. and/or Thunderbolt cable) configured to communicate over a wired connection with other devices in accordance with a suitable wired communication protocol. In certain examples, the network interface 112d includes the wired interface 112f and excludes the wireless interface 112e. In some examples, the electronics 112 excludes the network interface 112d altogether and transmits and receives media content and/or other data via another communication path (e.g., the input/output 111).

[0060] The audio components 112g are configured to process and/or filter data comprising media content received by the electronics 112 (e.g., via the input/output 111 and/or the network interface 112d) to produce output audio signals. In some examples, the audio processing components 112g comprise, for example, one or more digital-to-analog converters (DAC), audio preprocessing components, audio enhancement components, a digital signal processors (DSPs), and/or other suitable audio processing components, modules, circuits, etc. In certain examples, one or more of the audio processing components 112g can comprise one or more subcomponents of the processors 112a. In some examples, the electronics 112 omits the audio processing components 112g. In some examples, for instance, the processors 112a execute instructions stored on the memory 112b to perform audio processing operations to produce the output audio signals.

[0061] The amplifiers 112h are configured to receive and amplify the audio output signals produced by the audio processing components 112g and/or the processors 112a. The amplifiers 112h can comprise electronic devices and/or components configured to amplify audio signals to levels sufficient for driving one or more of the transducers 114. In some examples, for instance, the amplifiers 112h include one or more switching or class-D power amplifiers. In other examples, however, the amplifiers include one or more other types of power amplifiers (e.g., linear gain power amplifiers, class-A amplifiers, class-B amplifiers, class-AB amplifiers, class-C amplifiers. class-D amplifiers, class-E amplifiers, class-F amplifiers, class-G and/or class H amplifiers, and/or another suitable type of power amplifier). In certain examples, the amplifiers 112h comprise a suitable combination of two or more of the foregoing types of power amplifiers. Moreover, in some examples, individual ones of the amplifiers 112h correspond to individual ones of the transducers 114. In other examples, however, the electronics 112 includes a single one of the amplifiers I I2h configured to output amplified audio signals to a plurality of the transducers 114. In some other examples, the electronics 112 omits the amplifiers 112h.

[0062] The transducers 114 (e.g., one or more speakers and/or speaker drivers) receive the amplified audio signals from the amplifier 112h and render or output the amplified audio signals as sound (e.g., audible sound waves having a frequency between about 20 Hertz (Hz) and 20 kilohertz (kHz)). In some examples, the transducers 114 can comprise a single transducer. In other examples, however, the transducers 114 comprise a plurality of audio transducers. In some examples, the transducers 114 comprise more than one type of transducer. For example, the transducers 114 can include one or more low frequency transducers (e.g.. subwoofers, woofers), mid-range frequency transducers (e.g., mid-range transducers, midwoofers), and one or more high frequency transducers (e.g., one or more tweeters). As used herein, “low frequency” can generally refer to audible frequencies below about 500 Hz, “midrange frequency” can generally refer to audible frequencies between about 500 Hz and about 2 kHz, and “high frequency” can generally refer to audible frequencies above 2 kHz. In certain examples, however, one or more of the transducers 114 comprise transducers that do not adhere to the foregoing frequency ranges. For example, one of the transducers 114 may comprise a mid-woofer transducer configured to output sound at frequencies between about 200 Hz and about 5 kHz.

[0063] The playback device 110a can also optionally include display components 112k that are configured to play back visual content (e.g., video), either accompanying audio playback or independently of any audio playback. In various examples, these display components 112k can include video display elements and associated electronics. Examples of suitable display elements include a display screen (e.g., liquid crystal display (LCD), light-emitting diode (LED) display, organic LED (OLED) display, etc.), a projector, a heads-up display, a wearable display (e g., smart glasses, a smart watch, etc.), or any other suitable display technology that can play back visual content for viewing by one or more users. In some examples, the playback device 110a includes the display components 112k integrated within the same housing, for example in the case of a smart television or other such device. Additionally or alternatively, the playback device 1 10a can include display components 112k that are separate from but communicatively coupled to other elements of the playback device. For example, the playback device 110a can take the form of a soundbar that is communicatively coupled (e.g., via wired or wireless connection) to a television or other display component. In some examples, the playback device 110a can take the form of a dongle, set-top box, or other such discrete electronic component that can be communicatively coupled to a video display component such as a television, whether via a wired or wireless connection.

[0064] By way of illustration, SONOS, Inc. presently offers (or has offered) for sale certain playback devices including, for example, a "‘SONOS ONE." “MOVE,” “PLAYA,” “BEAM,” “PLAYBAR,” “PLAYBASE,” “PORT,” “BOOST,” “AMP,” and “SUB.” Other suitable playback devices may additionally or alternatively be used to implement the playback devices of example examples disclosed herein. Additionally, one of ordinary skilled in the art will appreciate that a playback device is not limited to the examples described herein or to SONOS product offerings. In some examples, for instance, one or more playback devices 110 comprises wired or wireless headphones (e g., over-the-ear headphones, on-ear headphones, in-ear earphones). In other examples, one or more of the playback devices 110 comprise a docking station and/or an interface configured to interact with a docking station for personal mobile media playback devices. In certain examples, a playback device may be integral to another device or component such as a television, a lighting fixture, or some other device for indoor or outdoor use. In some examples, a playback device omits a user interface and/or one or more transducers. For example, FIG. ID is a block diagram of a playback device I lOp comprising the input/output 111 and electronics 112 without the user interface 113 or transducers 114.

[0065] Figure IE is a block diagram of a bonded playback device HOq comprising the playback device 1 10a (Figure 1C) sonically bonded with the playback device HOi (e.g., a subwoofer) (Figure 1A). In the illustrated example, the playback devices 110a and HOi are separate ones of the playback devices 110 housed in separate enclosures. In some examples, however, the bonded playback device LlOq comprises a single enclosure housing both the playback devices 110a and HOi. The bonded playback device HOq can be configured to process and reproduce sound differently than an unbonded playback device (e.g.. the playback device 110a of Figure 1C) and/or paired or bonded playback devices (e g., the playback devices 1101 and 110m of Figure IB). In some examples, for instance, the playback device 110a is fullrange playback device configured to render low frequency, mid-range frequency, and high frequency audio content, and the playback device 1 lOi is a subwoofer configured to render low frequency audio content. In some examples, the playback device 110a, when bonded with the first playback device, is configured to render only the mid-range and high frequency components of a particular audio content, while the playback device HOi renders the low- frequency component of the particular audio content. In some examples, the bonded playback device HOq includes additional playback devices and/or another bonded playback device. Additional playback device examples are described in further detail below with respect to Figures 2A-2C. c. Suitable Network Microphone Devices (NMDs)

[0066] Figure IF is a block diagram of the NMD 120a (Figures 1A and IB). The NMD 120a includes one or more voice processing components 124 (hereinafter ‘'the voice components 124”) and several components described with respect to the playback device 110a (Figure 1C) including the processors 112a, the memory 112b, and the microphones 115. The NMD 120a optionally comprises other components also included in the playback device 110a (Figure 1C), such as the user interface 113 and/or the transducers 1 14. In some examples, the NMD 120a is configured as a media playback device (e.g., one or more of the playback devices 110), and further includes, for example, one or more of the audio components 112g (Figure 1C), the amplifiers 114, and/or other playback device components. In certain examples, the NMD 120a comprises an Internet of Things (loT) device such as. for example, a thermostat, alarm panel, fire and/or smoke detector, etc. In some examples, the NMD 120a comprises the microphones 115, the voice processing components 124, and only a portion of the components of the electronics 112 described above with respect to Figure IB. In some examples, for instance, the NMD 120a includes the processor 112a and the memory- 112b (Figure IB), while omitting one or more other components of the electronics 112. In some examples, the NMD 120a includes additional components (e.g., one or more sensors, cameras, thermometers, barometers, hygrometers).

[0067] In some examples, an NMD can be integrated into a playback device. Figure 1G is a block diagram of a playback device 1 lOr comprising an NMD 120d. The playback device 1 lOr can comprise many or all of the components of the playback device 110a and further include the microphones 115 and voice processing components 124 (Figure IF). The playback device 11 Or optionally includes an integrated control device 130c. The control device 130c can comprise, for example, a user interface (e.g., the user interface 113 of Figure IB) configured to receive user input (e.g., touch input, voice input) without a separate control device. In other examples, however, the playback device 11 Or receives commands from another control device (e.g., the control device 130a of Figure IB).

[0068] Referring again to Figure IF, the microphones 115 are configured to acquire, capture, and/or receive sound from an environment (e.g., the environment 101 of Figure 1A) and/or a room in which the NMD 120a is positioned. The received sound can include, for example, vocal utterances, audio played back by the NMD 120a and/or another playback device, background voices, ambient sounds, etc. The microphones 115 convert the received sound into electrical signals to produce microphone data. The voice processing components 124 receive and analyzes the microphone data to determine whether a voice input is present in the microphone data. The voice input can comprise, for example, an activation word followed by an utterance including a user request. As those of ordinary skill in the art will appreciate, an activation word is a word or other audio cue that signifying a user voice input. For instance, in querying the AMAZON® VAS, a user might speak the activation word "Alexa." Other examples include "Ok, Google" for invoking the GOOGLE® VAS and "Hey, Siri" for invoking the APPLE® VAS.

[0069] After detecting the activation word, voice processing components 124 monitor the microphone data for an accompanying user request in the voice input. The user request may include, for example, a command to control a third-party device, such as a thermostat (e.g., NEST® thermostat), an illumination device (e.g., a PHILIPS HUE ® lighting device), or a media playback device (e.g., a Sonos® playback device). For example, a user might speak the activation word “Alexa” followed by the utterance “set the thermostat to 68 degrees” to set a temperature in ahome (e.g., the environment 101 of Figure 1 A). The user might speak the same activation word followed by the utterance “turn on the living room” to turn on illumination devices in a living room area of the home. The user may similarly speak an activation word followed by a request to play a particular song, an album, or a playlist of music on a playback device in the home. d. Suitable Control Devices

[0070] Figure 1H is a partially schematic diagram of the control device 130a (Figures 1A and IB). As used herein, the term “control device” can be used interchangeably with “controller” or “control system.” Among other features, the control device 130a is configured to receive user input related to the media playback system 100 and, in response, cause one or more devices in the media playback system 100 to perform an action(s) or operation(s) corresponding to the user input. In the illustrated example, the control device 130a comprises a smartphone (e.g., an iPhone™ an Android phone) on which media playback system controller application software is installed. In some examples, the control device 130a comprises, for example, a tablet (e.g., an iPad™), a computer (e.g., a laptop computer, a desktop computer), and/or another suitable device (e.g., a television, an automobile audio head unit, an loT device). In certain examples, the control device 130a comprises a dedicated controller for the media playback system 100. In other examples, as described above with respect to Figure 1G, the control device 130a is integrated into another device in the media playback system 100 (e.g., one more of the playback devices 110. NMDs 120, and/or other suitable devices configured to communicate over a network).

[0071] The control device 130a includes electronics 132, a user interface 133, one or more speakers 134, and one or more microphones 135. The electronics 132 comprise one or more processors 132a (referred to hereinafter as “the processors 132a”). a memory 132b, software components 132c. and a network interface 132d. The processor 132a can be configured to perform functions relevant to facilitating user access, control, and configuration of the media playback system 100. The memon 132b can comprise data storage that can be loaded with one or more of the software components executable by the processor 132a to perform those functions. The software components 132c can comprise applications and/or other executable software configured to facilitate control of the media playback system 100. The memory 112b can be configured to store, for example, the software components 132c, media playback system controller application software, and/or other data associated with the media playback system 100 and the user.

[0072] The network interface 132d is configured to facilitate network communications between the control device 130a and one or more other devices in the media playback system 100, and/or one or more remote devices. In some examples, the network interface 132d is configured to operate according to one or more suitable communication industry’ standards (e.g.. infrared, radio, wired standards including IEEE 802.3. wireless standards including IEEE 802.11a, 802.11b, 802.11g, 802.1 In, 802.1 lac, 802.15, 4G, LTE). The network interface 132d can be configured, for example, to transmit data to and/or receive data from the playback devices 110, the NMDs 120, other ones of the control devices 130, one of the computing devices 106 of Figure IB, devices comprising one or more other media playback systems, etc. The transmitted and/or received data can include, for example, playback device control commands, state variables, playback zone and/or zone group configurations. For instance, based on user input received at the user interface 133, the network interface 132d can transmit a playback device control command (e.g., volume control, audio playback control, audio content selection) from the control device 130 to one or more of the playback devices 110. The network interface 132d can also transmit and/or receive configuration changes such as, for example, adding/removing one or more playback devices 110 to/from a zone, adding/removing one or more zones to/from a zone group, forming a bonded or consolidated player, separating one or more playback devices from a bonded or consolidated player, among others.

[0073] The user interface 133 is configured to receive user input and can facilitate 'control of the media playback system 100. The user interface 133 includes media content art 133a (e.g., album art, lyrics, videos), a playback status indicator 133b (e.g., an elapsed and/or remaining time indicator), media content information region 133c, a playback control region 133d, and a zone indicator 133e. The media content information region 133c can include a display of relevant information (e.g., title, artist, album, genre, release year) about media content currently playing and/or media content in a queue or playlist. The playback control region 133d can include selectable (e.g., via touch input and/or via a cursor or another suitable selector) icons to cause one or more playback devices in a selected playback zone or zone group to perform playback actions such as, for example, play or pause, fast forward, rewind, skip to next, skip to previous, enter/exit shuffle mode, enter/exit repeat mode, enter/exit cross fade mode, etc. The playback control region 133d may also include selectable icons to modify equalization settings, playback volume, and/or other suitable playback actions. In the illustrated example, the user interface 133 comprises a display presented on a touch screen interface of a smartphone (e.g., an iPhone™, an Android phone). In some examples, however, user interfaces of varying formats, styles, and interactive sequences may alternatively be implemented on one or more network devices to provide comparable control access to a media playback system.

[0074] As described in more detail below, in various examples the control device 130 can be configured to control or otherwise interact with video playback via a playback device 110. In some examples, the control device 130 can be used to control video playback via the playback device (e.g., selecting video content or other such media content for playback). Additionally or alternatively, the control device 130 can be used to present supplemental content to the user during video playback via the playback device 110. For example, the user may initiate, via the control device 130, playback of a television show on a playback device 110 (e.g., a smart television). During playback of the television show, supplemental content (e.g., other recommended shows, cast list, friends’ ratings, etc.) can be presented to the user via the interface 133 of the control device 130. In some examples, multiple control devices 130 can be used by the same or different users within the same environment to control the same playback device(s) 110. Moreover, the same or different supplemental content can be provided to those user(s) via the corresponding control devices 130.

[0075] The one or more speakers 134 (e.g.. one or more transducers) can be configured to output sound to the user of the control device 130a. In some examples, the one or more speakers comprise individual transducers configured to correspondingly output low frequencies, midrange frequencies, and/or high frequencies. In some examples, for instance, the control device 130a is configured as a playback device (e.g.. one of the playback devices 110). Similarly, in some examples the control device 130a is configured as an NMD (e.g., one of the NMDs 120), receiving voice commands and other sounds via the one or more microphones 135.

[0076] The one or more microphones 135 can comprise, for example, one or more condenser microphones, electret condenser microphones, dynamic microphones, and/or other suitable types of microphones or transducers. In some examples, two or more of the microphones 135 are arranged to capture location information of an audio source (e.g., voice, audible sound) and/or configured to facilitate filtering of background noise. Moreover, in certain examples, the control device 130a is configured to operate as playback device and an NMD. In other examples, however, the control device 130a omits the one or more speakers 134 and/or the one or more microphones 135. For instance, the control device 130a may comprise a device (e.g., a thermostat, an loT device, a network device) comprising a portion of the electronics 132 and the user interface 133 (e.g., a touch screen) without any speakers or microphones.

III. Example Audio Playback Devices Having Auxiliary Magnetic elements

[0077] As noted above, audio transducers can be characterized by a stiffness that resists movement of the membrane inward and outward along an excursion axis. This stiffness is due in part to mechanical components of the transducer (e.g., the suspension supporting the membrane) as well as to air pressure, particularly in the case of audio transducers mounted within an enclosure. To increase the efficiency of the audio transducer, it can be beneficial to reduce this stiffness.

[0078] As described in more detail below, a negative-stiffness magnetic assembly can be used to decrease the overall stiffness of an audio transducer. In some implementations, a voice coil is disposed over a stationary primary magnetic element (e.g., a magnetic pole piece, a cylindrical magnet, a magnet stack, etc.) and configured to move inward and outward along a drive axis in response to current driven through the voice coil. One or more moveable auxiliary magnetic elements can be coupled to the voice coil such that the auxiliary magnetic element(s) move in unison with the voice coil along the drive axis. These auxiliary magnetic element(s) can be configured and positioned such that, as the voice coil moves along the drive axis, the combined forces generated by the primary magnetic element(s) and the auxiliary magnetic element(s) amplify the voice coil movement over at least a portion of its range of motion. This amplification of movement imparts a negative stiffness, thereby reducing the total stiffness experienced by the voice coil and/or the membrane along its range of motion.

[0079] In some implementations, the auxiliary magnetic element(s) include one or more rings extending circumferentially around the drive axis. Additionally or alternatively, the auxiliary magnetic element(s) can take the form of a plurality of discrete magnetic bodies spaced apart from one another circumferentially around the drive axis. The auxiliary magnetic element(s) can also be disposed at various axial positions relative to the voice coil. Moreover, the discrete magnetic bodies of the auxiliary magnetic element(s) can be arranged in a common plane or at different axial positions relative to the voice coil.

[0080] Figure 2A is a block diagram of an example playback device 210. As illustrated, the playback device 210 includes an audio transducer 214 coupled with an enclosure 216. The enclosure 216 can also house electronics 212, which can be similar to electronics 112 described previously with respect to Figure 1C. As shown in Figure 2A, the playback device 210 can optionally include one or more other components 21 Oj (e.g., user interface components such as buttons or switches, etc.).

[0081] The audio transducer 214 includes a frame 216h, to which one or more membranes (e.g., diaphragms 220) can be coupled via one or more flexible surrounds 222. Each diaphragm 220 can also be operably driven by a corresponding drive unit 215 that includes a voice coil 228. Each drive unit 215 is configured such that, when the voice coil 228 moves axially along a drive axis (which can be parallel to the excursion axis), the diaphragm 220 moves axially along the excursion axis, thereby moving air to generate sound waves. In various examples. the drive unit 215 can take the form of a motor or motor assembly (e g., a linear motor assembly). The voice coil(s) 228 can each be disposed adjacent to a primary magnet 226 that provides a permanent magnetic field to facilitate movement of the voice coil 228 in response to current flowing therethrough.

[0082] As described in more detail below, one or more auxiliary magnetic elements 232 can also be provided for corresponding voice coil(s) 228. In operation, the auxiliary magnet(s) 232 can be coupled to a voice coil 228 such that the auxiliary magnet(s) 232 move axially in unison with the voice coil 228, and relative to the primary magnet(s) 226. The auxiliary magnet(s) 232 can be configured to provide an auxiliary magnetic field that imparts a negative stiffness to movement of the voice coil 228 and/or diaphragm 220 along the excursion axis, thereby at least partially canceling the mechanical stiffness of movement of these components along the excursion axis.

[0083] The transducer 214 can further include one or more suspension elements 230 that secure or stabilize movement portions of the transducer 214 relative to the frame 216h. For instance, the suspension elements 230 can take the form of structural elements extending between the frame 216h and the voice coil 228 and/or between the voice coil 228 and the diaphragm 220. Finally, the transducer 214 can optionally include one or more other additional components 214j as desired.

[0084] Figure 2B is a plan view of the audio transducer 214 shown in Figure 2A. Figures 2C and 2D are side cross-sectional view s of the audio transducer 214 taken along line 2C-2C at a rest position (Figure 2C) and at a position of inward excursion (Figure 2D), respectively. The audio transducer 214 can be incorporated into and/or include any of the features described elsewhere herein with respect to playback device 110. In some implementations, a playback device including the audio transducer 214 can include separate amplifiers for each drive unit 215. As described in more detail below; this can allow for separate corrective action to be taken for different drive units by adjusting the drive signal provided by one amplifier without necessarily making similar adjustments to other drive signals provided to other drive units. In various examples throughout, drive units 215 are described as including voice coils 228 surrounding primary magnets 226. However, in some implementations the drive units 215 can include any suitable membrane-actuating members and need not be limited to voice coils specifically. Although the illustrated example shows four drive units, in operation there may be any suitable number of drive units, including 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or more. [0085] With reference to Figures 2B-2D together, the audio transducer 214 includes two opposing diaphragms or membranes 220a. 220b (collectively “diaphragms 220”) each coupled to a frame 216h via corresponding surrounds 222a, 222b (collectively “surrounds 222”). The transducer 214 further includes four separate drive units 215a-d (collectively “drive units 215”). Two of the drive units (215a and 215b) are coupled to the first diaphragm 220a, while the other two drive units (215c and 215d) are coupled to the second diaphragm 220b. Together, the drive units 215 are configured to move the diaphragms 220 inward and outward along the excursion axis Al.

[0086] Each of the drive units 215 can include a corresponding driver static part configured to remain stationary with respect to the frame 216h and a driver moving part that is coupled to one of the diaphragms 220 and is configured to move with respect to the frame 216h in response to a drive signal, thereby causing the corresponding diaphragm 220 to move and produce sound. In the illustrated example, the driver stationary portion comprises a primary magnetic element 226 (which may include a single magnet, a stack of discrete magnets, or other suitable configuration) and the driver moving portion comprises a voice coil 228 and an auxiliary magnetic element 232. As illustrated, both the voice coil 228 and the auxiliary magnetic element 232 can extend circumferentially around the primary magnetic element 226. In various implementations, the voice coil 228 and the auxiliary' magnetic element 232 can be coupled together (e g., rigidly coupled) such that they move axially in unison in response to current passing through the voice coil 228. In the example shown in Figures 2C and 2D. the auxiliary magnetic element 232a of the first drive unit 215a is disposed axially below the corresponding voice coil 228a, and similarly the auxiliary magnetic element 232b of the second drive unit 215b is disposed axially below the corresponding voice coil 228b. However, in various implementations, and as described in more detail below, the axial position of the auxiliary magnetic elements 232 can vary, for instance being disposed axially below, above, or having portions that are both axially below, axially below, and/or axially aligned with or overlapping, the voice coil 228.

[0087] In operation, the presence of the auxiliary magnetic element 232 amplifies axial movement of the voice coil 228 away from a neutral rest position due to the interaction between the magnetic field of the primary magnetic element 226 and the magnetic field of the auxiliary magnetic element 232. This amplification thereby reduces stiffness of the voice coil 228 in the axial direction. In some implementations, the magnetic force of the auxiliary’ magnetic element 232 that amplifies axial movement of the voice coil 228 away from a neutral rest position at least partially cancels out mechanical forces that urge the voice coil 228 back towards the neutral rest position.

[0088] Although several aspects herein are described with respect to example audio transducers, the present technology can be usefully applied to any number of audio transducer configurations, including audio transduces with single or multiple membranes, with single or multiple drive units, and/or any suitable configuration. Various examples of suitable audio transducers that can be used in the context of the present technology can be found in the following commonly owned patents and patent applications, each of which is hereby incorporated by reference in its entirety: U.S. Patent No. 10,893,367, titled “Loudspeaker Unit with Multiple Drive Units.” U.S. Patent No. 11,197,102, titled “Distributed Transducer Suspension Cones (DTSC),” International Patent Application No. PCT/US2022/077272. titled “Speaker Device,” U.S. Patent No. 11,297,415, titled “Low Profile Loudspeaker Device,” U.S. Patent Application No. 17/424,181, titled “In Line Damper Bellows Dual Opposing Driver Speaker,” U.S. Patent Application No. 17/434,013, titled “Membrane Unit for Speaker Device,” U.S. Patent Application No. 17/602,314. titled “Linear Motor Magnet Assembly and Loudspeaker Unit,” U.S. Patent No. 11,166,107, titled “Speaker Unit with a Speaker Frame and Two Opposing Sound Producing Membranes,” and U.S. Patent Application No. 18/040.218, titled “Speaker Unit,” U.S. Patent Application No. 18/309,544, titled “Speaker Transducer.”

[0089] Figure 3 A is a schematic cross-sectional view of an example drive unit 215 for an audio transducer, and Figure 3B is a side perspective of the drive unit 215 shown in Figure 3A. As noted above, a given audio transducer can include one or more drive units 215, each of which can be coupled to a membrane such that as the voice coil 228 moves inward and outward along the drive axis A2, the membrane is moved inward and outward along an axis parallel to the drive axis A2.

[0090] In the example shown in Figures 3A and 3B, the primary magnetic element 226 takes the form of a magnetic stack including an upper primary' magnet 226a and a low er primary magnet 226b separated by a pole piece 302. Together, the elements of the primary magnetic element 226 are configured to provide a primary spatial magnetic field that is oriented along the drive axis A2, such that electrical current passing through the voice coil 228 causes the voice coil 228 to move along the drive axis A2. An auxiliary magnetic element 232 is also disposed about the drive axis A2 and can be coupled to the voice coil 228 such that the auxiliary magnetic element 232 and the voice coil 228 move together in unison along the drive axis A2. The auxiliary magnetic element 232 can be configured such that, when moved axially away from a rest position, an axial force is exerted on the auxiliary magnetic element 232 by virtue of the spatial magnetic field of the primary magnetic element 226. This axial force can be aligned to amplify movement of the voice coil 228 away from the neutral position, thereby contributing a negative stiffness to movement of the voice coil 228 along the drive axis A2. [0091] In various examples, the upper and lower primary magnets 226a and 226b can be arranged coaxially about the drive axis A2. In various examples, the upper and lower primary magnets 226a and 226 can take the form of generally cylindrical bodies, or other suitable shapes such as annular, disc-shaped, rectangular, or other configurations. Additionally, the shape, material, and/or configuration of the upper and lower primary magnets 226a and 226b can differ. Moreover, the magnet stack can include fewer magnets or more magnets than illustrated in Figures 3A and 3B. In the illustrated example, the upper primary magnet 226a is oriented with its north pole pointing upward, while the lower primary magnet 226a is oriented in the opposite direction such that the two south poles face one another. In some implementations, this polarity can be reversed such that the north poles of each primary magnet 226 faces toward one another. In various implementations, the upper and/or lower primary magnets 226a and 226b can be permanent magnets or electromagnetics. Additionally or alternatively, the upper and/or lower primary magnets 226a and 226b can be made of any suitable magnetic material, such as a ferromagnetic material. Examples of suitable materials include iron, nickel, cobalt, and ceramics and alloys thereof such as ferrite, neodymium, almco (aluminum-nickel-cobalt), and samarium cobalt. The pole piece 302 that axially separates the upper primary magnet 226a and the low er primary magnet 226b can likewise be made of a suitable magnetic material, such as iron.

[0092] The voice coil 228 can include a length of conductive wire that extends circumferentially about the primary magnetic element 226 with a radial gap betw een the voice coil 228 and the primary magnetic element 226 such that the voice coil 228 can move axially along the drive axis A2 without mechanical contact betw een the voice coil 228 and the primary magnetic element 226. Optionally the voice coil 228 is disposed on a cylindrical former. In the rest configuration depicted in Figures 3A and 3B, the voice coil 228 is axially aligned to be centered about the center of the pole piece 302 (i.e., with a center line of the voice coil 228 being equidistance from the upper primary magnet 226a and the lower primary magnet 226b). In various examples, depending on the particular construction of the drive unit 215 and additional components of the audio transducer, the voice coil 228 may be positioned at other axial locations while at a neutral rest position in which axial forces on the voice coil 228 are balanced out.

[0093] In the example illustrated in Figures 3A and 3B, the auxiliary magnetic element 232 takes the form of an annular ring extending circumferentially about the upper primary magnet 226a at a position that is spaced apart from the voice coil 228 along the drive axis A2. As noted previously, the auxiliary magnetic element 232 and the voice coil 228 can be rigidly coupled together such that they move in concert along the drive axis A2. For instance, the voice coil 228 and magnetic element 232 can be overmolded together into a unitary assembly, attached to a common carrier (e.g., a voice coil former), or otherwise coupled together. The auxiliary magnetic element 232 can be configured such that, when moved axially away from a rest position (as shown in Figures 3A and 3B), the interaction between the auxiliary magnetic element 232 and the primary magnetic element(s) 226 urge the auxiliary magnetic element 232 (and thereby also the voice coil 228, which is coupled thereto) to move further in the axial direction away from the rest position. In this way, the auxiliary magnetic element 232 amplifies axial movement of the voice coil 228 along the drive axis A2. Because this amplification occurs in both directions of movement away from the rest position (i.e., inward and outward along the drive axis A2), the auxiliary magnetic element 232 amplifies movement of the voice coil 228 in a balanced manner even when an auxiliary magnetic element 232 is only positioned about the upper primary magnet 226a and not about the lower primary’ magnet 226b.

[0094] As depicted in Figure 3A. the auxiliary magnetic element 232 can be oriented to substantially align with the spatial magnetic field provided by the primary magnetic element 226. For example, the poles of the auxiliary' magnetic element 232 are aligned along an axis substantially parallel to the drive axis A2, with the north pole pointed upward and the south pole pointed downward, similar to the orientation of the upper primary magnet 226a. In some examples, the magnetic orientation of the auxiliary magnetic element 232 can differ, however, such as having magnetic poles that are aligned along an axis that intersects the drive axis A2. [0095] In various implementations, the auxiliary' magnetic element 232 can take the form of a permanent magnet or an electromagnet. Additionally or alternatively, the auxiliary magnetic element 232 can be made of any suitable magnetic material, such as a ferromagnetic material. Examples of suitable materials include iron, nickel, cobalt, and ceramics and alloys thereof such as ferrite, neodymium, alnico (aluminum-nickel-cobalt), and samarium cobalt. The pole piece 302 that axially separates the upper primary magnet 226a and the lower primary magnet 226b can likewise be made of a suitable magnetic material including any of the previously mentioned ferromagnetic materials. In some implementations, the auxiliary magnetic element 232 can be made of a material that reduces the reluctance of the primary magnetic field provided by the primary magnetic element 226 (e.g., steel or other suitable material).

[0096] In various examples, the primary magnets 226a and 226b can have a maximum radial dimension that is greater than a maximum radial thickness of the auxiliary magnetic element 232. For instance, the maximum radial dimension of the primary magnets 226a and 226b can be at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 times the maximum radial thickness of the auxiliary magnetic element 232. Additionally, the primary magnets 226a and 226b can have a maximum axial height that is greater than a maximum axial height of the auxiliary magnetic element 232. For instance, the maximum axial height of the primary magnets 226a and 226b can be at least about 2, 3, 4. 5. 6, 7, 8. 9, 10. 1 1. 12. 13. 14, or 15 times the maximum axial height thickness of the auxiliary magnetic element 232.

[0001] Figures 4A and 4B are schematic cross-sectional and side perspective views, respectively, of another example drive unit 215 for an audio transducer. The drive unit 215 shown in Figures 4A and 4B can be similar to the drive unit 215 described above with respect to Figures 3A and 3B, except that the auxiliary magnetic element 232 takes the form of two discrete bodies: an upper auxiliary magnetic element 232a and a lower auxiliary magnetic element 232b. Each of the upper and lower auxiliary magnetic elements 232a and 232b can take the form of an annular ring or other suitable shape as noted above with respect to Figures 3A and 3B. As shown in Figures 4A and 4B, the upper auxiliary magnetic element 232a is disposed at a position axially above the voice coil 228 and the lower auxiliary magnetic element 232b is disposed at a position axially below the voice coil 228. In some implementations, the auxiliary magnetic elements 232a and 232b can be arranged symmetrically with respect to the voice coil 228, such that each is axially spaced apart from the voice coil 228 by the same distance. In the configuration shown in Figure 4A, the upper auxiliary magnetic element 232a has a magnetic orientation mirroring that of the upper primary magnet 226a (i.e., north pole pointed upward with the magnetic axis aligned along a direction parallel to the drive axis A2), and the lower auxiliary magnetic element 232b has a magnetic orientation mirroring that of the lower primary magnet 226b (i.e., north pole pointed downward with the magnetic axis aligned along a direction parallel to the drive axis A2). Additionally or alternatively, the upper auxiliary magnetic element 232a can be configured such that, at rest, a center line of the upper auxiliary magnetic element 232a is aligned with a center line of the upper primary magnet 226a. Similarly, the lower auxiliary magnetic element 232b can be configured such that, at rest, a center line of the lower auxiliary magnetic element 232b is aligned with a center line of the lower primary magnet 226b. In some implementations, one or both of the upper auxiliary magnetic element 232a and the lower auxiliary magnetic element 232b can assume other axial positions when at rest, for instance being disposed axially upward or downward with respect to a respective centerline of the upper primary magnet 226a or lower primary magnet 226b.

[0002] By virtue of placing the two auxiliary magnetic elements 232a and 232b on opposing sides of the voice coil 228, the amplification of axial movement of the voice coil 228 can be increased relative to configurations in which only a single auxiliary magnetic element 232 is present. Accordingly, this arrangement provides greater negative stiffness (further reducing the total stiffness) of the drive unit 215, which can increase the acoustic efficiency of the audio transducer. In some instances, however, it may be desirable to reduce the overall mass of the auxiliary magnet(s) 232. And while making annular rings thinner in both axial and radial dimensions can achieve such a mass reduction, making such thin rings can present manufacturing difficulties and lead to fragile components susceptible to damage or warpage during installation or operation. Accordingly, some examples of the present technology’ utilize a plurality of discrete magnetic bodies arranged circumferentially about the drive axis A2 instead of or in addition to unitary' annular magnets. Additional details of such configurations are described below with respect to Figures 5A-8.

[0003] Figures 5A and 5B are schematic cross-sectional and top side perspective views, respectively, of another example dnve unit 215 for an audio transducer. The drive unit 215 can be arranged similar to the configurations described above with respect to Figures 3A-4B, except that the auxiliary’ magnetic element 232 takes the form of a plurality' of discrete magnetic bodies that are arranged circumferentially about the drive axis A2. Specifically, a first plurality of magnetic bodies 232a are arranged about the upper primary magnet 226a and a second plurality of magnetic bodies 232b are arranged about the lower primary magnet 226b. In various examples, the magnetic bodies 232a and 232b can take a number of different forms, such as rod-shaped, cylindrical, bar-shaped, spherical, ellipsoidal, cubic, rectangular prisms, annular or semi-annular, conical, biconical. frustrum-shaped, bifrustum-shaped, or any other suitable shape or combination of shapes. The magnetic bodies 232a and 232b can be fixed with respect to the voice coil 228 such that the bodies 232 moves in conjunction with the voice coil 228 along the drive axis A2.

[0004] The number and arrangement of the magnetic bodies 232a and 232b can vary’. For instance, for each plurality of magnetic bodies 232, there may be any suitable number of bodies arranged about the drive axis A2, for instance 2. 3, 4, 5, 6, 7, 8, 9, 10. 11, 12, 13, 14, 15, 16 or more magnetic bodies. The magnetic bodies can be arranged with radial symmetry such that each magnetic body 232a is circumferentially spaced apart from adjacent magnetic bodies 232a by the same distance. Alternatively, the circumferential spacing may be non-uniform. In the illustrated example, each of the magnetic bodies 232a are spaced apart from the drive axis A2 by the same distance such that the bodies 232a are arranged on a circular arc about the drive axis A2. However, in some implementations the radial spacing away from the drive axis A2 may vary, with some magnetic bodies 232a positioned nearer to the drive axis A2 and other magnetic bodies 232a positioned further. In total, the plurality of magnetic bodies 232a may be configured to produce an auxiliary’ magnetic field that is radially symmetrical about the drive axis A2, thereby promoting balance in the radial direction as the voice coil 228 moves along the drive axis A2. In some implementations, the plurality⁷ of magnetic bodies 232a may be arranged and configured to produce an auxiliary’ magnetic field that is radially asymmetric. In such instances, this radial asymmetry can optionally be counterbalanced by a corresponding radial asymmetry on another drive unit that is also coupled to the same membrane. For instance, if a given membrane has two drive units coupled to opposing ends of the membrane, a radial asymmetry⁷ in the auxiliary' magnetic fields for each of the drive units can cancel one another out so that the membrane as a whole moves axially along an excursion axis without wobbling or rocking.

[0005] In various implementations, the discrete magnetic bodies 232a can be substantially identical (e.g., having the same shape and magnetic orientation) or the configuration may differ among the magnetic bodies 232a. For instance, different magnetic bodies 232 may have different shapes, may be arranged with different magnetic orientations, or otherwise vary from one to the next. In the case of magnetic orientations, each magnetic body 232 can be magnetically oriented similar to the corresponding primary magnet 226 (e g., magnetic bodies 232a can have their north poles facing upward and aligned parallel to the upper primary magnet 226a and the lower magnetic bodies 232b can have their north poles facing downward and aligned parallel to the lower primary magnet 226b). In some examples, the magnetic orientation of some or all of the magnetic bodies can differ, for instance having polarity reversed, or having the magnetic poles aligned along an axis that is not parallel with the drive axis A2. The northsouth axis of some or all of the magnetic bodies may be oriented radially inward (e.g., with the north pole facing radially outward and south pole facing radially inward, or vice versa) or maybe oriented circumferentially (e.g., with the north pole facing toward a clockwise direction when viewed from above, and the south pole facing toward a counterclockwise direction when viewed from above), or any combination thereof. In some instances, the combination of different polarities can be selected to achieve a desired overall auxiliary magnetic field (e.g., with individual magnetic bodies arranged to provide a Halbach array).

[0006] Functionally, the combined magnetic interactions between the plurality of discrete magnetic bodies 232a, 232b, and the primary’ upper and lower primary magnets 226a, 226b can be similar to the interaction described above with respect to auxiliary magnets in the form of unitary annular rings. By providing a plurality of discrete bodies, however, the individual components may be more readily manufacturable and less fragile. Moreover, by varying the position, arrangement, and orientation of the various bodies, the magnetic interactions can be more finely tuned in a way that improves the negative-stiffness curve provided by these auxiliary magnetic elements over the excursion range of the voice coil 228 (e.g., achieving a more linear force-displacement curve over a linear range of motion of the voice coil 228).

[0007] In various examples, the individual magnetic bodies 232a and 232b can have a maximum radial thickness that is smaller than a maximum radial dimension of the of the primary magnets 226a and 226b. For instance, the maximum radial dimension of the primary magnets 226a and 226b can be at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 times the maximum radial thickness of an individual auxiliary magnetic body 232a or 232b. Additionally, the primary magnets 226a and 226b can have a maximum axial height that is greater than a maximum axial height of each of the auxiliary magnetic bodies 232. For instance, the maximum axial height of the primary magnets 226a and 226b can be at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 times the maximum axial height of the individual auxiliary’ magnetic bodies 232a and 232b.

[0008] Figures 6A and 6B are schematic cross-sectional and side perspective views, respectively, of another example drive unit 215 for an audio transducer. This drive unit 215 can be similar to that described above with respect to Figures 5A and 5B, except that the auxiliary magnetic element 232 takes the form of three subsets of magnetic bodies 232a, 232b, and 232c that are all spaced about the upper primary magnet 226a. As illustrated, a first subset of magnetic bodies 232a are arranged at a first axial position with respect to the voice coil 228, aligned along plane DI. A second subset of magnetic bodies are arranged at a second axial position along plane D2, and a third subset of magnetic bodies are arranged at a third axial position along plane D3. In various implementations, the number of subsets (and corresponding axial positions) and the number of individual magnetic bodies within each subset can vary, for instance having only a single magnetic body a subset, and/or having 4, 5, 6, 7, 8 or more different subsets with different corresponding axial positions. As noted above with respect to Figures 5A and 5B, the particular shape, magnetic orientation, and other properties of the individual magnetic bodies 232 can vary, with the particular configuration selected to achieve the desired auxiliary magnetic field.

[0009] In the example shown in Figure 6B, each of the subsets of magnetic bodies are grouped together circumferentially, such that the first subset of magnetic bodies 232a are adjacent to one another without intervening bodies, the second subset of magnetic bodies 232b are likewise adjacent to one another without intervening bodies, and so forth. In various examples, however, the particular arrangement of subsets can vary such that they alternate or are interspersed in the circumferential direction. Additionally or alternatively, the particular subsets of magnetic bodies can be arranged to have radial symmetry. As noted previously, in some instances a radial asymmetry, if present, can be counteracted by a corresponding radial asymmetry in another drive unit of the same transducer.

[0010] Figures 7A-7G illustrate example shapes for auxiliary magnetic elements 232 for use in a drive unit for an audio transducer. As noted previously, the individual magnetic bodies 232 can take any suitable shape, including cylindrical, rectangular prismatic, spherical or ellipsoidal, cubic, semi-annular or arc-shaped, conical, biconical, or any combination or modification thereof.

[0011] Figure 8 illustrates an example magnetic element support assembly 800 for use in a drive unit 215 for an audio transducer. The support assembly 800 includes an annular body 802 with a plurality of receptacles holding discrete magnetic bodies 232 that together serve as an auxiliary magnetic element. The support assembly 800 can be disposed about the primary magnet, and optionally can be coupled to the voice coil of the drive unit. In some examples, the material of the annular body 802 is not itself ferromagnetic, for instance being made of plastic. The material can preferably be lightweight so as to reduce the overall mass of the assembly, while the discrete magnetic bodies 232 provide the desired magnetic properties. As noted above, such a configuration can provide magnetic properties similar to a unitary’ ring magnet but in a more durable and readily manufacturable configuration.

IV. Conclusion

[0012] The above discussions relating to playback devices, controller devices, playback zone configurations, and media content sources provide only some examples of operating environments within which functions and methods described below may be implemented. Other operating environments and/or configurations of media playback systems, playback devices, and network devices not explicitly described herein may also be applicable and suitable for implementation of the functions and methods.

[0013] The description above discloses, among other things, various example systems, methods, apparatus, and articles of manufacture including, among other components, firmware and/or software executed on hardware. It is understood that such examples are merely illustrative and should not be considered as limiting. For example, it is contemplated that any or all of the firmware, hardware, and/or software examples or components can be embodied exclusively in hardware, exclusively in software, exclusively in firmware, or in any combination of hardware, software, and/or firmware. Accordingly, the examples provided are not the only ways) to implement such systems, methods, apparatus, and/or articles of manufacture.

[0014] Additionally, references herein to "example" means that a particular feature, structure, or characteristic described in connection with the example can be included in at least one example embodiment or implementation of an invention. The appearances of this phrase in various places in the specification are not necessarily all referring to the same example, nor are separate or alternative examples mutually exclusive of other examples. As such, the examples described herein, explicitly and implicitly understood by one skilled in the art, can be combined with other examples.

[0015] The specification is presented largely in terms of illustrative environments, systems, procedures, steps, logic blocks, processing, and other symbolic representations that directly or indirectly resemble the operations of data processing devices coupled to networks. These process descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. Numerous specific details are set forth to provide a thorough understanding of the present disclosure. However, it is understood to those skilled in the art that certain examples of the present disclosure can be practiced without certain, specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring examples of the examples. Accordingly, the scope of the present disclosure is defined by the appended claims rather than the foregoing description of examples.

[0016] When any of the appended claims are read to cover a purely software and/or firmware implementation, at least one of the elements in at least one example is hereby expressly defined to include a tangible, non-transitory medium such as a memory, DVD, CD, Blu-ray, and so on, storing the software and/or firmware.

[0017] The disclosed technology is illustrated, for example, according to various examples described below. Various examples of examples of the disclosed technology are described as numbered examples (1, 2, 3, etc.) for convenience. These are provided as examples and do not limit the disclosed technology. It is noted that any of the dependent examples may be combined in any combination, and placed into a respective independent example. The other examples can be presented in a similar manner.

[0018] Example 1. An audio playback device comprising: a membrane configured to move inward and outward along an excursion axis; a voice coil operably coupled to the membrane, the voice coil configured to move axially inward and outward over an excursion range; a negative-stiffness assembly comprising: a stationary first magnetic element aligned along a drive axis parallel to the excursion axis; and a plurality of moveable second magnetic elements arranged circumferentially around the drive axis and coupled to the voice coil, wherein the plurality of moveable second magnetic elements create a magnetic force that at least partially cancels a mechanical force on the membrane as it moves along the excursion axis.

[0019] Example 2. The audio playback device of any one of the preceding Examples, wherein the plurality of moveable second magnetic elements comprises a plurality of discrete magnetic bodies disposed at different circumferential positions around the drive axis.

[0020] Example 3. The audio playback device of any one of the preceding Examples, wherein two or more of the discrete magnetic bodies are disposed at the same axial position relative to the voice coil.

[0021] Example 4. The audio playback device of any one of the preceding Examples, wherein the discrete magnetic bodies are arranged at positions axially offset from the voice coil.

[0022] Example 5. The audio playback device of any one of the preceding Examples, wherein two or more of the discrete magnetic bodies are disposed at different axial positions from one another relative to the voice coil.

[0023] Example 6. The audio playback device of any one of the preceding Examples, wherein the plurality' of discrete magnetic bodies comprises: a first subset circumferentially spaced apart from one another about the drive axis and aligned at a first axial position relative to the voice coil; and a second subset circumferentially spaced apart from one another about the drive axis and aligned at a second axial position relative to the voice coil, wherein the second axial position is further from the voice coil than the first axial position.

[0024] Example 7. The audio playback device of any one of the preceding Examples, wherein the first subset and the second subset are disposed alternately in the circumferential direction about the drive axis.

[0025] Example 8. The audio playback device of any one of the preceding Examples, wherein the plurality of discrete magnetic bodies further comprises: a third subset circumferentially spaced apart from one another about the drive axis and aligned at a third axial position relative to the voice coil, wherein the third axial position is closer to the voice coil than the first axial position.

[0026] Example 9. The audio playback device of any one of the preceding Examples, wherein the plurality of moveable second magnetic elements comprises at least 8 discrete magnetic bodies.

[0027] Example 10. The audio playback device of any one of the preceding Examples, wherein the discrete magnetic bodies are arranged in a radially symmetrical manner about the drive axis.

[0028] Example 11. The audio playback device of any one of the preceding Examples, wherein at least two of the discrete magnetic bodies are arranged with different magnetic orientations.

[0029] Example 12. The audio playback device of any one of the preceding Examples, wherein one or more of the discrete magnetic bodies has a cylindrical shape, a bar shape, a spherical shape, an ellipsoid shape, a cubic shape, a rectangular prism shape, a semi-annular shape, a conical shape, a frustum shape, a bifrustum shape, or a biconical shape.

[0030] Example 13. The audio playback device of any one of the preceding Examples, wherein the plurality of discrete magnetic bodies each have a height along the axial direction that is less than a height of the stationary first magnetic element.

[0031] Example 14. The audio playback device of any one of the preceding Examples, further comprising a support member coupled to each of the discrete magnetic bodies, wherein the support member is coupled to the voice coil.

[0032] Example 15. The audio playback device of any one of the preceding Examples, wherein the support member comprises an annular ring with corresponding receptacles for each of the discrete magnetic bodies. [0033] Example 16. The audio playback device of any one of the preceding Examples, wherein the moveable second magnetic elements are rigidly coupled to the voice coil such that the relative positions of the voice coil and the moveable second magnetic elements do not change as the voice coil moves inward and outward over the excursion range.

[0034] Example 17. The audio playback device of any one of the preceding Examples, wherein the plurality of moveable second magnetic elements comprises a plurality of rings each extending circumferentially around the drive axis, wherein the rings are disposed at different axial positions relative to the voice coil.

[0035] Example 18. The audio playback device of any one of the preceding Examples, wherein the stationary magnetic element comprises a magnetic stack including a plurality of discrete magnets arranged coaxially along the drive axis.

[0036] Example 19. The audio playback device of any one of the preceding Examples, wherein the stationary magnetic element comprises at least one cylindrical magnet.

[0037] Example 20. The audio playback device of any one of the preceding Examples, wherein the stationary first magnetic element comprises a permanent magnet or an electromagnet.

[0038] Example 21. The audio playback device of any one of the preceding Examples, wherein the plurality' of moveable second magnetic elements each comprises a permanent magnet or an electromagnet.

[0039] Example 22. The audio playback device of any one of the preceding Examples, wherein the voice coil extends circumferentially around the drive axis and axially overlaps at least a portion of the stationary first magnetic element over at least a portion of the excursion range.

[0040] Example 23. An audio playback device comprising: a membrane; a membrane actuating element configured to move the membrane inward and outward along an excursion axis; a stationary first magnetic element; and a plurality of moveable second magnetic elements coupled to the membrane actuating element, wherein the plurality of moveable second magnetic elements create a magnetic force that at least partially cancels a mechanical force on the membrane as it moves along the excursion axis.

[0041] Example 24. The audio playback device of any one of the preceding Examples, wherein the membrane actuating element comprises a voice coil.

[0042] Example 25. The audio playback device of any one of the preceding Examples, wherein the plurality of moveable second magnetic elements. [0043] Example 26. The audio playback device of any one of the preceding Examples, wherein the stationary first magnetic element is aligned along a drive axis, and wherein the plurality of moveable second magnetic elements comprises a plurality of discrete magnetic bodies disposed at different circumferential positions around the drive axis.

[0044] Example 27. The audio playback device of any one of the preceding Examples, wherein the stationary first magnetic element is aligned along a drive axis, wherein the plurality of moveable second magnetic elements comprises a plurality of rings each extending circumferentially around the drive axis, and wherein the rings are disposed at different axial positions relative to the membrane actuating element.

[0045] Example 28. A drive assembly for an audio playback device, the drive assembly comprising: a stationary first magnetic element configured to provide a spatial magnetic field aligned along a drive axis; a voice coil configured to move axially inward and outward relative to the stationary first magnetic element; and a moveable second magnetic element coupled to the voice coil and disposed at a first position about the drive axis; a moveable third magnetic element coupled to the voice coil and disposed at a second position about the drive axis such that the moveable second magnetic element and the moveable third magnetic element are spaced apart from one another (i) circumferentially about the drive axis; (ii) in the axial direction along the drive axis; or (iii) both (i) and (ii).

[0046] Example 29. The drive assembly of any one of the preceding Examples, wherein the moveable second magnetic element and the moveable third magnetic element create a magnetic force that imparts a negative stiffness to the voice coil as it moves axially inward and outward.

Claims

1. An audio playback device comprising: a membrane configured to move inward and outward along an excursion axis; a voice coil operably coupled to the membrane, the voice coil configured to move axially inward and outward over an excursion range; and a negative-stiffness assembly comprising: a stationary’ first magnetic element aligned along a drive axis parallel to the excursion axis; and a plurality' of moveable second magnetic elements arranged circumferentially around the drive axis and coupled to the voice coil, wherein the plurality of moveable second magnetic elements create a magnetic force that at least partially cancels a mechanical force on the membrane as it moves along the excursion axis.

2. The audio playback device of claim 1, wherein the plurality' of moveable second magnetic elements comprises a plurality of discrete magnetic bodies disposed at different circumferential positions around the drive axis.

3. The audio playback device of claim 2, wherein two or more of the discrete magnetic bodies are disposed at the same axial position relative to the voice coil.

4. The audio playback device of claim 2 or claim 3. wherein the discrete magnetic bodies are arranged at positions axially offset from the voice coil.

5. The audio playback device of claim 2 or claim 4, wherein two or more of the discrete magnetic bodies are disposed at different axial positions from one another relative to the voice coil.

6. The audio playback device of any one of claims 2-5, wherein the plurality' of discrete magnetic bodies comprises: a first subset circumferentially spaced apart from one another about the drive axis and aligned at a first axial position relative to the voice coil; and a second subset circumferentially spaced apart from one another about the drive axis and aligned at a second axial position relative to the voice coil, wherein the second axial position is further from the voice coil than the first axial position.

7. The audio playback device of claim 6. wherein the first subset and the second subset are disposed alternately in the circumferential direction about the drive axis.

8. The audio playback device of claim 6 or claim 7, wherein the plurality' of discrete magnetic bodies further comprises: a third subset circumferentially spaced apart from one another about the drive axis and aligned at a third axial position relative to the voice coil, wherein the third axial position is closer to the voice coil than the first axial position.

9. The audio playback device of any one of claims 2-8. wherein the plurality’ of moveable second magnetic elements comprises at least 8 discrete magnetic bodies.

10. The audio playback device of any one of claims 2-9, wherein the discrete magnetic bodies are arranged in a radially symmetrical manner about the drive axis.

11. The audio playback device of any one of claims 2-10, wherein at least two of the discrete magnetic bodies are arranged with different magnetic orientations.

12. The audio playback device of any one of claims 2-11, wherein one or more of the discrete magnetic bodies has a cylindrical shape, a bar shape, a spherical shape, an ellipsoid shape, a cubic shape, a rectangular prism shape, a semi-annular shape, a conical shape, a frustum shape, a bifrustum shape, or a biconical shape.

13. The audio playback device of any one of claims 2-12, wherein the plurality' of discrete magnetic bodies each have a height along the axial direction that is less than a height of the stationary first magnetic element.

14. The audio playback device of any one of claims 2-13, further comprising a support member coupled to each of the discrete magnetic bodies, wherein the support member is coupled to the voice coil.

15. The audio playback device of claim 14, wherein the support member comprises an annular ring with corresponding receptacles for each of the discrete magnetic bodies.

16. The audio playback device of any one of claims 1-15, wherein the moveable second magnetic elements are rigidly coupled to the voice coil such that the relative positions of the voice coil and the moveable second magnetic elements do not change as the voice coil moves inward and outward over the excursion range.

17. The audio playback device of any one of claims 1-16, wherein the plurality of moveable second magnetic elements comprises a plurality of rings each extending circumferentially around the drive axis, wherein the rings are disposed at different axial positions relative to the voice coil.

18. The audio playback device of any one of claims 1-17, wherein the stationary magnetic element comprises a magnetic stack including a plurality of discrete magnets arranged coaxially along the drive axis.

19. The audio playback device of any one of claims 1-18, wherein the stationary magnetic element comprises at least one cylindrical magnet.

20. The audio playback device of any one of claims 1-19, wherein the stationary first magnetic element comprises a permanent magnet or an electromagnet.

21. The audio playback device of any one of claims 1-20, wherein the plurality of moveable second magnetic elements each comprises a permanent magnet or an electromagnet.

22. The audio playback device of any one of claims 1-21, wherein the voice coil extends circumferentially around the drive axis and axially overlaps at least a portion of the stationary first magnetic element over at least a portion of the excursion range.

23. An audio playback device comprising: a membrane; a membrane actuating element configured to move the membrane inward and outward along an excursion axis; a stationary first magnetic element; and a plurality of moveable second magnetic elements coupled to the membrane actuating element, wherein the plurality of moveable second magnetic elements create a magnetic force that at least partially cancels a mechanical force on the membrane as it moves along the excursion axis.

24. The audio playback device of claim 23, wherein the membrane actuating element comprises a voice coil.

25. The audio playback device of claim 23 or claim 24, wherein the plurality’ of moveable second magnetic elements.

26. The audio playback device of any one of claims 23-25, wherein the stationary first magnetic element is aligned along a drive axis, and wherein the plurality of moveable second magnetic elements comprises a plurality of discrete magnetic bodies disposed at different circumferential positions around the drive axis.

27. The audio playback device of any one of claims 23-26, wherein the stationary first magnetic element is aligned along a drive axis, wherein the plurality of moveable second magnetic elements comprises a plurality’ of rings each extending circumferentially' around the drive axis, and wherein the rings are disposed at different axial positions relative to the membrane actuating element.

28. A drive assembly' for an audio playback device, the drive assembly comprising: a stationary’ first magnetic element configured to provide a spatial magnetic field aligned along a drive axis; a voice coil configured to move axially inward and outward relative to the stationary first magnetic element; and a moveable second magnetic element coupled to the voice coil and disposed at a first position about the drive axis; a moveable third magnetic element coupled to the voice coil and disposed at a second position about the drive axis such that the moveable second magnetic element and the moveable third magnetic element are spaced apart from one another (i) circumferentially about the drive axis; (ii) in the axial direction along the drive axis; or (iii) both (i) and (ii).

29. The drive assembly of claim 28, wherein the moveable second magnetic element and the moveable third magnetic element create a magnetic force that imparts a negative stiffness to the voice coil as it moves axially inward and outward.