HK1213122B - Multi-driver earbud - Google Patents

Description

Multi-driver earbuds

Embodiments of the present invention relate to earphones, also known as earbuds, that fit in a user's ear canal and have a crossover network and multiple speaker drivers.Other embodiments are also described.

Background Art

In-ear headphones or earbuds continue to be popular because they can deliver adequate sound quality while having a convenient, compact form factor and being lightweight. Professional-quality in-ear headphones often use balanced armature drivers, which can be designed to faithfully reproduce low-frequency sounds or high-frequency sounds. However, balanced armature drivers generally do not operate consistently across the entire audible frequency range. To overcome this limitation, it has been proposed to use multiple balanced armature drivers within an in-ear headphone. In such cases, a crossover network is also provided to divide the audio signal's spectrum into two regions, a low-frequency region and a high-frequency region, and to use separate drivers to reproduce the sound in each region. Professional-quality headphones may also have eartips or earmuffs, which can be custom-molded or generic, allowing for a snug fit that acoustically seals the user's ear canal. This allows for higher-quality low-frequency or bass sounds to be heard, in addition to lower auditory background noise.

A typical sealed earbud has a housing or cup that houses the driver. A silicone or rubber boot with a sound channel formed therein is fitted over the front end of the driver to hold the driver in place and ensure that the driver output is sealed from the external environment. A cover made of a rigid material (the opposite material of the boot) is then pushed onto the boot to essentially complete the rigid earphone housing. A nozzle extends from the front of the cover and aligns with the channel in the boot to receive the sound produced by the driver. A flexible ear tip is then fitted to the nozzle. Although this arrangement has proven effective in delivering adequate sound performance while being sufficiently small and light enough for everyday consumer users with a variety of activities, providing good sound fidelity over most (if not all) of the typical consumer's hearing range, general (i.e., non-customized) in-ear headphones suitable for mass production present a challenge, particularly in packaging multiple drivers within the compact confines of the earbud housing.

Summary of the Invention

An embodiment of the present invention is an earbud having an earbud cup, wherein a first driver housing and a second driver housing are disposed within the earbud cup. The first driver housing has a rear side, a front side, a top surface, a bottom surface, and a sound output tube extending outwardly from the front side. The second driver housing has a top side, a bottom side, a front side, a rear side, and a sound output opening formed in the front side, but is substantially devoid of the sound output tube. The rear side of the second housing is positioned a) adjacent to the front side of the first housing and b) behind the outlet of the sound output tube of the first housing.

In one embodiment, in the first housing, the top surface has a larger area than the rear or front sides. Furthermore, in the second housing, the front surface has a larger area than the top or bottom sides. An example of such a housing is a parallelepiped-shaped driver, in which the diaphragm in each housing can be positioned substantially parallel to the faces of the housing rather than the sides. Each driver housing can contain a single balanced armature driver to produce its corresponding sound.

In another embodiment, the earbud cup includes a low driver housing, a mid driver housing, and a high driver housing. The three housings are arranged relative to one another, resulting in a more compact envelope capable of producing sound with good fidelity. Specifically, the mid driver housing and the low driver housing are stacked one on top of another, i.e., the top surface of the low housing lies substantially flat against the bottom surface of the mid housing, while the high housing is oriented so that its rear surface is positioned adjacent to the front side of the low housing and behind the outlet of the sound output tube of the mid housing. A sound output opening is formed in the front face of the high housing, but the sound output tube is substantially absent.

In one embodiment, the high driver housing houses a single balanced armature motor coupled to drive a diaphragm oriented substantially parallel to the front and rear faces of the high housing, while the low and mid driver housings may contain either balanced armatures or dynamic moving coil motors, or a mix of both. This arrangement works particularly well when the top surface of the low driver housing has a larger area than the rear or front sides of the low driver housing, and the bottom surface of the mid driver housing has a larger area than its front or rear sides. In one embodiment, each of the low and mid housings is substantially parallelepiped (e.g., the rectangular shape of a matchbox), with two opposing faces each having a larger area than any side face of the housing.

In one embodiment, the driver housing is assembled into a protective cover, which can be flexible and resilient enough to hold the driver housing as a single component. Two channels are formed in the protective cover, which are aligned with the two sound output ports of the driver housing. In an embodiment where the earbud has at least three driver housings, the high driver housing can be given its own channel in the protective cover, while the low driver housing and the middle driver housing must share another channel. In another embodiment, the protective cover has a third channel dedicated to the low housing, where another sound output tube extends outward and upward from the left or right side of the low driver housing and then connects to a dedicated channel in the protective cover. In that case, each of the three driver housings uses its own or corresponding channel through the protective cover.

To complete the earbud housing, a cover is provided having an opening that aligns with the outlet of the channel in the protective cover and is large enough to surround the outlet. The cover can be made of a material that is more rigid than the protective cover, for example, similar to the material used to make the housing or cup. The protective cover can be fitted into the front of the cover so that the cover completely surrounds the cover; the cover can then be snap-fitted or otherwise attached to the front of the cup. A nozzle can extend forward from the cover, where it aligns with the cover opening. The nozzle can provide an uninterrupted space at the cover opening that communicates with the outlet ports of the first and second channels. A flexible eartip can be fitted to the nozzle to provide the user with a snug and acoustically sealed in-ear headphone experience. In such an embodiment, the nozzle can have an equivalent radius-to-length ratio in the range of 1/4 to 1/7 of the additive constant. This specific range works effectively with the relatively compact arrangement of three driver housings in dual-channel or triple-channel versions with protective covers.

In yet another embodiment, the arrangement of the driver housings and the way they are assembled into the protective cover allow space to accommodate an inertial sensor integrated circuit (e.g., a digital accelerometer chip) located below the bottom surface of the low driver housing and behind the protective cover. The inertial sensor can be used as part of a non-acoustic microphone to detect the voice of a user wearing the headphones. In addition, an acoustic microphone can be assembled in the protective cover, which can be used as an error microphone in an active noise cancellation system. Another hole can be formed in the protective cover so that sound from the space between the front of the protective cover and the back of the cover can reach the acoustic inlet of the microphone. The hole can be positioned so that the inlet of the acoustic microphone is located directly behind it, for example, where the acoustic microphone is located below the bottom side of the second driver housing (or high driver housing) and in front of the front side of the first driver housing (or low driver housing). This allows the acoustic microphone to be used not only as an error microphone for an active noise control system, but also as a component of a near-end user or talker voice pickup system. This system may be particularly effective when external acoustic background noise is passively reduced by the sealing properties of the flexible ear tip.

The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the present invention includes all systems and methods that can be implemented by all suitable combinations of the various aspects summarized above, as well as the various aspects disclosed in the following detailed description and particularly pointed out in the claims filed with this application. Such combinations have particular advantages not specifically set forth in the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the present invention are described by way of example and not limitation in the drawings, in which like reference numerals indicate similar elements. It should be noted that references to "one" or "an" embodiment in this disclosure are not necessarily to the same embodiment, and they mean at least one. Furthermore, a single figure may depict multiple embodiments of the invention, or aspects of different embodiments, as explained in the detailed description, in order to limit the total number of figures (for reasons of simplicity).

1 is an exploded view of an earbud with a multi-way driver having a first driver housing and a second driver housing and a crossover circuit according to an embodiment of the present invention.

2A is a cross-sectional view of an earbud with a three-way driver.

2B is a perspective view of the three-way driver assembly shown in FIG. 2A .

3A is a front perspective view of a protective cover having two ports or channels.

FIG. 3B is a rear perspective view of the protective cover in FIG. 3A .

4A is a cross-sectional view of an assembly having a protective cover, an accelerometer, an acoustic microphone, and three driver housings to be installed into an earbud housing.

FIG. 4B is a bottom view of the assembly of FIG. 4A .

4C is a rear perspective view of the protective cover used in the embodiment of FIGS. 4A and 4B , showing another aperture for coupling to a microphone acoustic inlet.

5 is a perspective view of an assembly of three driver housings, wherein each of the housings has its sound output port formed in an outer wall of the housing.

Figure 6 is a disassembled view of several different earplugs, including one having three driver housings and two sound output ports connected to a two-port protective cover assembly, another having three driver housings and three sound output ports connected to a three-port protective cover assembly, and a flexible circuit assembly suitable for three-way or two-way earplugs.

DETAILED DESCRIPTION

In this section, we will explain several preferred embodiments of the present invention with reference to the accompanying drawings. Whenever the shapes, relative positions and other aspects of the components described in the embodiments are not clearly defined, the scope of the present invention is not limited to the components shown, and the components shown are only for illustrative purposes.

Starting with Figure 1, which is an exploded view of a two-way earbud having a first driver housing or shell 2 and a second driver housing or shell 4. At the rear is the earbud housing 1, also known as the earbud cup, which can be made of a relatively rigid material, such as molded plastic. The earbud housing 1 can be used to accommodate different versions of a multi-way driver assembly, including one with two driver housings 2, 4 and another with three driver housings (see Figure 2A). It is also used to enclose an electrical cable, the proximal end of which terminates in a jumper circuit 27 inside the housing 1 and the distal end of which terminates in an accessory connector (e.g., tip ring sleeve, TRRS, headphone plug - not shown). The cable is used to route the original audio electrical signal from an external device (not shown) to the input of the jumper circuit 27. In one embodiment, the low pass filter and high pass filter outputs of the jumper circuit 27 are electrically connected by a flexible circuit 28 to corresponding electrical terminals of the first driver housing 2 and the second driver housing 4, respectively. In another embodiment, crossover circuit 27 or any one or more of its constituent electronic filters may be omitted, for example, where the desired low-pass and/or high-pass behavior can be acoustically achieved by appropriately tuning the driver itself. In both embodiments, first driver housing 2 may be referred to herein as part of the low-frequency driver, and second driver housing 4 may be referred to herein as part of the high-frequency driver.

The drivers, both housings 2 and 4, are capable of generating sound content represented in a raw audio signal. The sound content can be, for example, music from digital music or movie files stored locally on an external device or streamed from a remote server, processed by an audio processor (not shown) and converted into a raw audio signal. Alternatively, the sound content can be the voice of a remote user of a communication system, including an external device, during a voice or video call with a near-end user wearing earbuds. Examples of external devices include smartphones, portable digital media players, tablet computers, and laptop computers.

The earbud cup or housing 1 has an open front end as shown, which receives a multi-way driver assembly, which in this case has at least two different driver housings, namely a first driver housing 2 and a second driver housing 4. In one embodiment, each driver housing is generally a polyhedron with flat faces and straight edges, but more generally, some of the faces and edges may be curved. There is a manufacturing advantage when the faces and edges of the driver housings are respectively flat and straight. In the specific example shown in Figure 1, each driver housing is essentially formed as a parallelepiped with a corresponding primary sound output port formed in the wall of each parallelepiped. However, the description of the "faces" and "sides" of the driver housings below also applies to other polyhedrons. Moreover, for the sake of clarity, references to "front" and "rear," "left" and "right," and "vertical" and "horizontal" are used only to refer to relative orientations and should not be interpreted as having absolute or limiting meanings.

For the first driver housing 2, the sound output port 7 is formed as a tube, as shown, which extends outwardly from an outer wall called the front side 8. In one embodiment, the sound output port 7 is the main sound output port of the driver housing 2. The rear side of the driver housing 2 is arranged further back than the earphone housing 1 and is substantially parallel to the front side 8 in the case of the parallelepiped shown. In that case, the left side, right side, top surface and bottom surface complete the encapsulation. The sound radiating member or diaphragm 9 is located inside the driver housing 2 and, as shown, can be oriented substantially parallel, i.e., substantially perpendicular to the sides of the driver housing, or substantially parallel to the top or bottom surface of the driver housing 2. This is in contrast to the substantially perpendicular orientation of the diaphragm 3 in the second driver housing 4. Alternatively, the diaphragm 9 can be oriented substantially vertically, i.e., substantially parallel to the sides (rather than the faces) of the driver housing 2. A motor inside the attached housing 2 (not shown) vibrates the diaphragm 9 in response to a low-pass filtered audio signal from the jumper circuit 27, thereby producing sound.

The second driver housing 4 is also a substantially parallelepiped shell, in this example formed by a front 6, a rear, left and right sides, and a top and bottom side. The internal diaphragm 3 is substantially parallel to the front 6. The housing 4 is oriented so that its main sound output port is formed in the outer wall of the housing, referred to as the front 6, while the rear side (opposite the front 6 in this case) is arranged adjacent to the front side 8 of the housing 2. Adjacent here can mean that there is no intervening space or air gap between the rear side and the front side, but there can be one or more layers connecting the two, for example, a layer of adhesive material or a layer of vibration dampening material. The rear side of the second driver housing 2 is also positioned behind the outlet of the sound output port 7 of the first housing 2.

The sound output port 5 of the second driver housing 4 is a hole or opening, essentially devoid of any sound output tube extending therefrom. In the particular embodiment shown, while the sound output port 7 of the first housing 2 is shown as actually extending forward to form a tube with a short nozzle, no such nozzle is present for the sound output port 5 of the second housing 4. The sound output port 5 can be substantially flush with the front face 6, resting flat against the inner surface of the protective cover 10. This helps reduce the depth (front-to-back direction) of the multi-way driver assembly and can also increase sound output (loudness) in the frequency range relevant to a particular nozzle design (e.g., having a particular _Re /L ratio).

The two driver housings 2, 4 can be clamped, held, or supported by the two-port boot 10, which can be made of a resilient material, as opposed to the more rigid material used for the earphone housing 1. Examples include silicone or rubber-type materials that can stretch and be flexible, thereby gripping the exterior of the driver housings 2, 4 once they are assembled into the boot opening. The two-port boot 10 has a first channel 13 and a second channel 14 formed in its bottom portion as shown, and these channels align with the sound output ports of the driver housings when the driver housings 2, 4 are assembled into the boot 10. An example of the two-port boot 10 is shown in Figures 3A and 3B.

The front face or front surface of the bottom of the protective cover 10 is formed with an outer ridge 21. As shown, the outer ridge 21 can completely surround the outlets of the channels 13, 11, thereby providing an acoustic seal when pressed against the inner face of the cover 12 (see FIG1). A mixing space 36 can be formed in the front truncated portion, where the sound from the two channels 13, 11 can be mixed while being isolated from ambient noise due to being surrounded by the outer ridge 21.

Referring to FIG3B , which shows a perspective rear view of the two-port protective cover 10 of FIG3A , it can be seen that an inner ridge 35 is formed on the inner surface of the protective cover 10, completely surrounding the channel 11. The purpose of the inner ridge 35 is to prevent ambient sound from leaking into the channel 13 and disrupting the sound produced by the high-frequency driver (housing 2). Note that a similar ridge may not be required for the channel 13 because the sound output port 7 used is an extended tube, which, due to its contact with the wall of the channel 13, can provide more acoustic isolation (than simply forming an opening for the sound output port 5 of the high-frequency driver).

The protective shield 10 can be sized so that the cover 12 can fit over the front of the protective shield 10, so that the elasticity of the material of the protective shield 10 serves to push against the inside of the cover 12, thereby holding the protective shield in place. For example, the front and front sides of the protective shield 10 can be sized to fit snugly into the interior cavity of the cover 12 (as shown in FIG1 , accessed from the rear of the cover). The cover 12 can be made of a material that is more rigid than the protective shield 10, for example, similar to the material used for the earphone housing 1, such as molded plastic. The cover 12 also serves to complete the relatively rigid earphone housing by, for example, snap-fitting or snugly fitting onto the open end of the earphone housing 1 by other means.

The lid 12 has an opening in its face that is aligned with the outlets of the mixing space 36 and the first and second channels 13, 11 in the protective cover 10 and is large enough to communicate with these outlets. However, the opening is smaller than the area of the outer ridge 21, making it less likely that ambient/background noise will enter the lid opening. A nozzle 15 extends forward from the front surface of the lid 12, where it is aligned with the lid opening. The nozzle 15 can be a generally circular sound tube (e.g., having an elliptical cross-section) that may or may not taper along its length and provides an uninterrupted space communicating with the outlets of the mixing space 36 and the first and second channels 13, 11 (through the lid opening). The nozzle 15 can be tuned to deliver improved sound quality, for example, such that its ratio _Re /L (ratio of equivalent radius _Re to length L) is in the range of 1/4 to 1/7 plus a constant, with the understanding that increasing L can achieve a reduced effect.

In the particular embodiment shown in FIG1 , the earplug is a sealing earplug in which an ear tip or earmuff 14 is provided that is attached to a cover 12 to acoustically seal against the user's ear canal. The ear tip 14 can be made of a flexible foam-type material or other suitable material that can adapt to the shape of the user's ear canal wall, thereby providing an acoustic seal, for example, an acoustic seal that completely surrounds a channel (shown in dotted lines) formed in the ear tip 14. The channel is designed to receive a front portion of a nozzle 15 therein. A suitable mechanism is also provided to keep the ear tip 14 attached to the cover 12, including the nozzle 15, as the user repeatedly inserts and removes the earplug into their ear.

In the embodiment of Figure 1, the second driver housing 4 can be a housing for a balanced armature driver, wherein a sound output port 5 (an opening, such as a slot or a circular hole) is formed in a front face 6 which is part of the outer wall of the driver housing 4. In one embodiment, the housing wall completely encloses the chamber in which the diaphragm 3 is positioned so as to be substantially parallel to the front face 6 as shown. The diaphragm 3 is the primary sound generating or radiating member and will vibrate in accordance with the audio signal converted by the motor. The audio signal that drives the balanced armature motor can be a high pass filtered version of the original audio signal delivered to the earbud by the cable 26 - see Figure 1. The jumper circuit 27 can high pass filter the original audio signal at one of its outputs and can also low pass filter the original audio signal at the other of its outputs to achieve the operation of the two-way earbud shown in Figure 1. The low pass filtered version is sent to the input electrical terminals of the first driver housing 2. Note that in a three-way earbud (such as the one shown in FIG2A ), the jumper circuit 27 can also perform bandpass filtering at another output, with the bandpass filtered version being sent to the input electrical terminals of the third driver housing (the midrange speaker housing 18 in FIG2A ). Alternatively, the jumper circuit 27 can be omitted for a particular driver, allowing the original audio signal in this case to be routed to the driver input terminals in that driver housing.

Turning now to FIG2A , a cross-sectional view of a three-way earbud is shown, which has a three-way driver in which a woofer housing is provided that is larger than the mid-range speaker housing, which in turn is larger than the tweeter housing. In this case, the earbud housing 1 and cover 12 can be substantially similar to those of the two-way earbud shown in FIG1A . In addition, the ear tip 14 can also be similar. As another similarity, the two-port protective cover 10 can also be reused for the three-way driver, in which the upper channel 13 is shared by both the low-frequency driver (i.e., woofer 16) and the mid-range driver 18. This can be achieved by providing a sound output port in the top surface of the woofer 16 housing, which, as shown, is aligned with the input port formed in the bottom surface of the housing of the mid-range speaker 18. The thickest arrows in FIG2A represent the low-frequency or bass sounds produced by the woofer 16, while the medium-thick arrows represent the mid-frequency sounds produced by the mid-range driver 18, and the thin arrows represent the high-frequency sounds produced by the tweeter 17. As shown, the high-frequency sounds from the tweeter 17 are given their own dedicated channels 11 in the two-port protective cover 10.

The low-frequency driver housing, i.e., the housing of woofer 16, has a rear side, a front side, a top surface, and a bottom surface, with the rear side where the driver input electrical terminals 33 are exposed and connected to the flexible circuit 28. The low-frequency driver housing is stacked flat below the midrange driver 18 housing, which also has a rear side, a front side, a top surface, and a bottom surface, with the rear side where the driver input electrical terminals 32 are exposed and connected to the flexible circuit 28. In addition, the housing of midrange speaker 18 has a sound output port 7 that extends from the front side (see also FIG2B ) as an acoustic duct through which both low-frequency and midrange sounds are delivered to the mixing space 36 of protective cover 10—see FIG3A . Stacking midrange speaker 18 and woofer 16 can also be described as positioning the bottom surface of the housing of midrange speaker 18 adjacent to the top surface of the housing of woofer 16.

To complete the three-way driver assembly, the housing of tweeter 17 is oriented so that its sound output port 5 is formed only as an opening in the front 6 of the housing, while the rear of the housing is adjacent to the front side 19 of the housing of woofer 16. In addition, the rear of the tweeter housing is positioned behind the outlet of the sound output tube of the midrange speaker 18 housing. In this configuration, the outlet of the midrange sound output tube is substantially aligned with the front of the tweeter housing, so as to reduce the depth of the three-way driver assembly. This arrangement is also shown in FIG2B , where in this case the sound output port 7 emerges from the front side 8 of the midrange speaker 18 housing, while the sound output port 5 is formed in the front 6 of the tweeter 17 housing.

Note that in the embodiment of Figures 2A and 2B , each of the driver housings is substantially parallelepipedal. For example, like the bottom surface, the top surface of the woofer housing has a larger area than either the rear or front sides of the housing. Furthermore, each of the top and bottom surfaces of the midrange speaker housing can have a larger area than either of the side surfaces. For the housing of tweeter 17, each of the front and back surfaces has a larger area than the left and right sides, but not necessarily larger than the top and bottom sides. With this arrangement, in one embodiment, as shown, diaphragm 3 of tweeter 17 is oriented substantially vertically, or substantially parallel to the front and back of the tweeter housing, while diaphragms 9b and 9a of midrange speaker 18 and woofer 16, respectively, are substantially horizontal, or parallel to the top and bottom surfaces of those housings. See Figure 4A , which shows a cross-sectional view of a three-way driver assembly and, more specifically, diaphragm 3 of tweeter 17, diaphragm 9a of woofer 16, and diaphragm 9b of midrange speaker 18.

Figures 2A and 2B also illustrate how flexible circuit 28 is connected to its jumper circuit 27. In this case, jumper circuit 27 has three outputs, providing low-pass, band-pass, and high-pass filtered versions of the original audio signal delivered to the earbud via cable 26. As can also be seen in Figure 2B, in this embodiment, flexible circuit 28 has two sections: one section extends substantially vertically and connects electrical terminal 33 of woofer 16 to the low-pass filter output and electrical terminal 32 of midrange speaker 18 to the band-pass filter output, while the other section runs backward from electrical terminal 34 of tweeter 17 along the top surface of the illustrated woofer housing and connects to the high-pass filter output. Note also how one section of flexible circuit 28 extends along the top surface of the woofer housing and along the left side of the midrange housing, while the right side of the midrange is positioned closer to the right side of the woofer housing, as shown in Figure 2B. This arrangement also helps reduce the volume of space required inside earbud housing 1.

In one embodiment, still referring to the three-way earbud of Figure 2A and the three-way driver assembly of Figure 2B, the tweeter 17 may have a balanced armature motor inside its housing coupled to drive the diaphragm 3. As for the motors used in the woofer 16 and midrange speaker 18, these motors may or may not be of the balanced armature type, as one or both may alternatively be a variation of electrodynamics.

Referring now to FIG. 4A , a cross-sectional view of a three-way driver assembly in combination with an acoustic microphone 38 is shown. The latter can be used as part of a digital acoustic pickup circuit (not shown), which may include analog-to-digital conversion circuitry connected to the flex circuit 27 and positioned adjacent to the flex circuit 27. Microphone 38 can be mounted in a so-called "digital" boot 39. The latter can be substantially similar to the two-port boot 10 described above, except that, as shown in FIG. 4B and FIG. 4C , an additional opening or aperture is created to allow sound from the mixing space 36 between the front of the boot 39 and the rear of the cover 12 to reach the acoustic inlet of microphone 38. In the example shown here, microphone 38 is located below the bottom side of the tweeter 17 housing and in front of the front side of the woofer 16 housing. This arrangement is particularly space-efficient because the lower section of the flex circuit 28 can be electrically connected to microphone 38, extending from the electrical output terminals of microphone 38 along the bottom surface of the woofer housing, then upward to connect to the terminals of woofer 16, and then forward to connect to the terminals of midrange speaker 18. The digitized audio signal picked up by microphone 38 represents the sound in mixed space 36, which is essentially the sound produced in the ear cavity of the user wearing the earbuds. This digitized audio signal can be delivered via cable 26 (see FIG. 2A ) to an active noise control or cancellation (ANC) processor, which can be implemented in an external device (which also generates the original audio signal that is sent to the three-way driver for conversion into sound). In that case, microphone 38 can be referred to as an error microphone, which the ANC processor uses to pick up residual acoustic noise that may be heard by the user during ANC processing operations.

4B and 4C , the opening for sound to reach microphone 38 comprises a through-hole segment, i.e., a hole extending through the wall of boot 39, and a groove segment, i.e., a groove formed in the outer surface of the boot wall, connecting the through-hole segment to an area in front of the front face of boot 39, located within the perimeter of outer ridge 21. This can be best seen in the bottom view of boot 39 shown in FIG4B . To achieve such a groove segment, as shown in FIG4B , a corresponding portion of outer ridge 21 has been removed (or not formed). This, in turn, allows sound from mixing space 36 to diffuse across the front face of boot 39 and then pass along the groove segment and subsequently the through-hole segment before reaching the acoustic inlet of microphone 38, thereby reaching the location of acoustic microphone 38.

Returning to Figures 4A and 4B , these figures also illustrate another embodiment of the present invention, in which an inertial sensor 37 (e.g., a digital accelerometer chip) can be connected to the exterior of the flexible circuit 27 (with the microphone 28 connected to its interior), positioned beneath the bottom surface of the woofer 16 and behind a protective cover 39. This allows the bottom of the inertial sensor 37 to directly contact the inner surface of the outer wall of the earbud housing 1, thereby better picking up vibrations caused by bone conduction when the earbud wearer speaks. To improve performance, vibration dampening or absorbing material can be added between the inertial sensor 37 and the bottom surface of the woofer 16 to attenuate the pickup of low-frequency vibrations generated when the woofer 16 converts the original audio signal. Here, the flex circuit 27 is used to route the digitized inertial signal (from the inertial sensor 37) to the cable 26 (see Figure 2A ), which in turn routes the signal to an external audio device. Within the external device, the inertial signal can be processed by a combined acoustic and non-acoustic voice activity detection processor to determine whether the user (wearing the earbuds) is speaking.

FIG5 is a perspective view of an assembly of three driver housings, each of which has a corresponding sound output port formed in its outer wall. This embodiment is similar to the 3-way driver assembly shown in FIG2B , except that the housing of the woofer 16 has a sound output port 20 (in this case, a tube) extending outward and upward from the right outer wall of the housing. The outlet of this bass output tube (sound output port 20) fits into a channel 25 formed in the bottom of the protective cover of the 3-port protective cover 22. The latter has two additional channels 24, 23, as shown in the figure, which are aligned with the outlets of the mid-range speaker sound output port 7 and the tweeter sound output port 5, respectively. For the 3-port protective cover 22, the mixing space 36 (see FIG3A for the 2-port protective cover 10) is open to the outlet ports of all three channels 23, 24, and 25, so that in the space between the front of the protective cover 29 and the back of the cover 12, the individual sounds are first mixed together outside the protective cover 29. This arrangement is similar to the earplug with 2-port boot 10 shown in FIG. 1A , with the understanding that for 2-port boot 22 , the cover opening from which the nozzle 15 extends forwardly will communicate with the mixing space 36 while remaining within the perimeter of the outer ridge 21 .

FIG6 is an exploded view of several different earplugs described above, all of which can share the same housing 1, cover 12, and earmuff 14, but use different combinations of shields and multi-way driver assemblies. In one embodiment, a 2-port shield 10 is used in combination with a 2-way driver assembly (see FIG1 ) or a 3-way driver assembly (see FIG2B ). In another embodiment, a 3-port shield 22 is used in combination with a 3-way driver assembly that has independent sound output ports for all three drivers, extending from their respective housing walls and then directly communicating with their respective channels in the shield 22—see FIG5 ). In another embodiment, a digital shield 39 is used that allows an acoustic microphone 38 to be mounted on the flexible circuit 28, where it should be clear that either a 2-way or 3-way driver assembly can be used in such an embodiment.

While certain embodiments have been described and shown in the accompanying drawings, it will be understood that such embodiments are intended to illustrate the broad invention only and not to limit it, and that the invention is not limited to the specific constructions and arrangements shown and described, as various other modifications will occur to those skilled in the art. For example, while the driver housing shown in the accompanying drawings is a polyhedron, the "sides" of the driver housing may alternatively be a single, continuous, smooth wall (like a ring) that surrounds the driver housing, rather than discrete faces in a polyhedron. Furthermore, while Figures 1 and 2A show sealed earplugs in which a flexible earmuff or eartip 14 is fitted to the cover 12, an alternative is to omit the eartip 14 and shape the cover 12 and nozzle 14 to achieve a loose-fitting, non-sealed earplug. The description is therefore to be regarded as exemplary and not restrictive.

Claims (18)

1. An earplug, comprising: Earplug cup; A low-profile driver housing having a rear side, a front side, a top surface, and a bottom surface; A middle driver housing having a rear side, a front side, a top surface, and a bottom surface, and a sound output tube extending from the front side of the middle driver housing, wherein the bottom surface of the middle driver housing is configured to be adjacent to the top surface of the lower driver housing; and A high-driver housing having a top side, a bottom side, a front side, and a rear side, a sound output opening formed in the front side of the high-driver housing, wherein the rear side of the high-driver housing is configured such that a) it is adjacent to the front side of the low-driver housing, and b) it is located behind the outlet of the sound output tube of the middle-driver housing. 2. The earplug of claim 1, wherein each of the top surface of the low-driver housing and the bottom surface of the low-driver housing has a larger area than the rear or front side of the low-driver housing. 3. The earplug of claim 1, further comprising a driver electrical terminal exposed on the rear side of the low driver housing and another driver electrical terminal exposed on the rear side of the middle driver housing. 4. The earplug according to claim 3, further comprising: Driver electrical terminals exposed on the left or right side of the high-drive housing; and A flexible circuit, wherein the flexible circuit extends along the top surface of the low driver housing and lays wires backward from the driver electrical terminals of the high driver housing. 5. The earplug of claim 1, further comprising a balanced armature motor located within the high-drive housing, the balanced armature motor being coupled to drive a diaphragm oriented parallel to the front of the high-drive housing. 6. The earplug of claim 1, further comprising a sound output tube extending outward and then upward from the left or right side of the low-driver housing. 7. The earplug of claim 1, further comprising a protective cover having a first channel and a second channel formed therein, wherein the low driver housing, the medium driver housing and the high driver housing are fitted into the protective cover, and the first channel and the second channel are respectively aligned with the sound output tube of the medium driver housing and the sound output opening of the high driver housing. 8. The earplug of claim 7, further comprising a sound output tube extending outward and then upward from the left or right side of the low-driver housing. A third channel is formed within the protective cover, and the third channel is aligned with the outlet of the sound output tube extending from the low-driver housing. 9. The earplug of claim 7, further comprising a cap having an opening aligned with and large enough to surround the outlets of the first and second channels in the protective cover. 10. The earplug of claim 9, further comprising an ear tip fitted onto the cover. 11. The earplug of claim 10, further comprising an acoustic microphone fitted into the protective cover, and another hole formed in the protective cover, the other hole allowing sound from the space between the front of the protective cover and the rear of the cover to reach the acoustic inlet of the microphone. 12. The earbud of claim 11, wherein the microphone is located below the bottom side of the high-driver housing and in front of the front side of the low-driver housing. 13. The earplug of claim 11, further comprising an inertial sensor located in the earplug cup. 14. The earpiece of claim 13, further comprising flexible circuitry electrically connected to the microphone, the inertial sensor, and the low-driver housing and the mid-driver housing, wherein the flexible circuitry extends rearward and then upward from the microphone along the bottom surface of the low-driver housing to connect to the low-driver housing and the mid-driver housing. 15. The earplug of claim 9, further comprising a port extending forward from the cap, wherein the port is aligned with the opening of the cap, wherein the port provides an uninterrupted space communicating with the outlet ports of the first and second channels at the opening of the cap, wherein the port is fitted with an ear tip, and wherein the port has an equivalent radius to length ratio in the range of 1/4 to 1/7 plus a constant. 16. An earplug, comprising: Earplug cup; A parallelepiped housing for an intermediate frequency driver, the intermediate frequency driver parallelepiped housing being stacked on top of a parallelepiped housing for a low frequency driver; A high-frequency driver parallelepiped housing, the rear of which is adjacent to the front of the low-frequency driver parallelepiped housing, and the sound output port of the high-frequency driver parallelepiped housing is an opening in the front of the high-frequency driver parallelepiped housing, without any sound output tube; and An elastic protective cover that grips the low-frequency driver parallelepiped housing, the mid-frequency driver parallelepiped housing, and the high-frequency driver parallelepiped housing inside the earplug cup. 17. The earplug of claim 16, further comprising a balanced armature motor within the parallelepiped housing of the high-frequency driver, the balanced armature motor being coupled to vibrate a diaphragm, wherein the diaphragm is positioned parallel to the front of the parallelepiped housing of the high-frequency driver. 18. The earplug of claim 16, further comprising: bridging circuit; and A flexible circuit, which is electrically connected to the bridging circuit, wherein the flexible circuit is laid with wires extending backward from the driver input terminal in the high-frequency driver parallelepiped housing and along the top surface of the low-frequency driver parallelepiped housing adjacent to the left or right side of the mid-frequency driver parallelepiped housing.