EA000929B1 - Pannel-form loudspeakers - Google Patents

Abstract

1. A panel-form loudspeaker and comprising a distributed mode acoustic radiator with a transducer coupled to vibrate the radiator to produce bending waves causing it to resonate, characterized by a second transducer to produce a signal in response to resonance of said radiator due to incident acoustic energy. 2. A panel-form loudspeaker according to claim 1, characterized in that the radiator is mounted in a surrounding frame by means of an interposed resilient suspension. 3. A panel-form loudspeaker according to claim 1 or 2, characterized in that the radiator comprises a stiff lightweght panel having a cellular core sandwiched between skins. 4. A panel-form loudspeaker according to any preceding claim, characterized by a further transducer on the radiator to produce a signal in response to resonance of the radiator due to incident acoustic energy, and by means for comparing the signal generated by said further transducer with that of those generated by the said second transduser(s). 5. A panel-form loudspeaker according to claim 4, characterized in that the comparison means comprises a signal receiver and conditioner and signal output means.

Description

FIELD OF THE INVENTION

The invention relates to loudspeakers and, more specifically, to loudspeakers containing acoustic emitting elements in the form of a panel.

State of the art

From a UK patent application GB-A-2262861, a panel-shaped loudspeaker is known comprising:

a resonant multimode radiating element, which is an integral laminated panel of a sandwich type structure made of two outer layers of material with a core between them having a honeycomb structure, and the panel is made such that it has a bending stiffness (B) in all directions to the third degree panel mass per unit surface area (µm) of at least 10;

installation means that supports the panel or which freely fastens the panel to the supporting body so as not to dampen vibrations;

and means of an electromechanical drive connected to the panel, which serves to excite a multimode resonance in the panel of the emitter under the influence of an input electrical signal within the working frequency band of the loudspeaker.

SUMMARY OF THE INVENTION

In embodiments of the present invention, elements have been used, in essence, structure and configuration, corresponding mainly and / or in particular to the technical solutions described in the PCT application simultaneously pending No. WO 97/09842 of the applicant for this application. Thus, such elements are capable of transferring and distributing the input vibrational energy through shear waves in the working zone (s) that extend transversely to the thickness, but not necessarily to the edges of the element (s), have a configuration with or without anisotropy of bending stiffness for the distribution of resonant vibrational components in the specified zone (s) so that a favorable acoustic connection with the surrounding air is achieved, and have predefined preferred locations and whether there are areas within the specified zone for transducer means, especially active or moving parts of which affect the activity of acoustic vibrations in the specified zone (s), and to which signals, usually electric, corresponding to the acoustic content of such activity, are received. International application No. WO 97/09842 provides for the use of such elements in passive acoustic devices without transducers, for example, for reverberation, for acoustic filtration or for acoustic sounding of a space or a room; or in active acoustic devices with transducers, for example, in an unusually wide range of sound sources or loudspeakers, where the input signals must be converted to the specified sound, or, for example, in microphones, when the sound is converted to other signals.

The present invention mainly relates to active acoustic devices in the form of speakers. The elements described above are hereinafter referred to as distributed mode acoustic emitters and are disclosed in the above PCT application and / or in this application as specific elements.

The invention relates to a loudspeaker made in the form of a panel and having an element capable of transferring and distributing the input vibrational energy by means of transverse waves in at least one working zone extending transversely to its thickness for distributing resonant vibrational components over said zone, as well as having predefined preferred locations or areas in the specified area for the transducer and the transducer mounted on the specified element in one of the specified locations areas or sections to inform the element of the oscillation and cause its resonance with the formation of an acoustic emitter, which at resonance provides the generation of an acoustic output signal. What is new is that the loudspeaker is also a microphone and contains a second transducer mounted on the element in one of the locations or sections to generate an output signal under the influence of the resonance of the element caused by the incident acoustic energy. The element can be installed in the surrounding frame using an elastic suspension located between this element and the frame. The element may comprise a rigid lightweight panel having a honeycomb core enclosed between the outer layers. The pendant can be attached to the edge of the panel. The first and second converters can be completely and exclusively mounted on the emitter. At least two of these second transducers can be installed in predetermined preferred locations or areas on the emitter. An additional transducer can be provided on the emitter in a predetermined location or area to generate a signal under the influence of the resonance of the emitter caused by the incident acoustic energy, and means can also be provided for comparing the signal generated by the specified additional transducer with the signal (s), generated (and) indicated (s) by the second (s) converter (s). The comparison tool may include a receiver and a signal conditioner and signal output means.

The invention is disclosed with reference to the accompanying drawings, in which FIG. 1 is a distributed mode speaker disclosed in the simultaneously pending international application No. WO 97/09842;

FIG. 2a is a partial section along AA in FIG.

one;

FIG. 2b is a scaled-up cross-section of a distributed mode radiator of the type shown in FIG. 2a showing two alternative designs;

FIG. 3 is an embodiment of a distributed mode speaker microphone in accordance with the present invention; and FIG. 4 is a perspective view of a piezoelectric transducer.

In FIG. 1 shows a loudspeaker (81) in the form of a panel of the type that is disclosed in the simultaneously pending international application No. WO 97/09842, comprising a rectangular frame (1) supporting an elastic suspension (3) located on the inner periphery of the frame and supporting an acoustic emitting panel ( 2) distributed mode. A converter (9), for example, of the type described in detail with reference to simultaneously pending international applications No. WO 97/09859; WO 97/09861; WO 97/09858, is installed completely and exclusively on or in the panel (2) at a predetermined location defined by the dimensions X and Y, and this location is calculated as described in the simultaneously pending international application No. WO 97/09842 in order to apply bending to the panel vibrations to make the panel resonate to emit an acoustic output signal.

The converter (9) is controlled by a signal amplifier (10), for example, an audio frequency amplifier connected to the converter by conductors (28). The requirements regarding the load and power of the amplifier can be completely normal, the same as in conventional cone speakers, with a sensitivity of about 86-88 dB / W under load conditions for the room. The total load resistance of the amplifier reaches 6 ohms, with a power of 20-80 watts. When the core of the panel and / or the outer layers are made of metal, they can serve as a heat sink to remove heat from the transducer and thereby improve energy distribution.

In FIG. 2a and 2b show partial cross sections of the speaker (81) of FIG. 1. In FIG. 2a, it is shown that the frame (1), the suspension (3) and the panel (2) are connected by means of adhesive (adhesive) joint seams (20). Suitable frame materials are light frames, like picture frames, diecast from a metal, such as an aluminum alloy, or plastic. Suitable materials for suspension are resilient materials such as foam rubber and foams. Suitable adhesives for joining joints (20) are adhesives such as epoxy adhesive, acrylic and cyano-acrylate adhesive.

In FIG. 2b, it is shown on an enlarged scale that the panel (2) is a rigid light panel having a core (22), for example of rigid foam (97), i.e. a structured polyvinyl chloride or honeycomb matrix (98), for example a matrix of metal foil, plastic or a similar honeycomb structure material with cells spaced across a plane of a panel enclosed between opposing outer layers (21), for example, of paper, cardboard, plastic, metal foil or sheet. When the layers are made of plastic, they must be reinforced with fibers, for example carbon, fiberglass, Kevlar material (registered trademark (ZTZ)) or a similar material, using the known method of increasing their modules.

Thus, the materials used for the outer layers and reinforcing elements include carbon, glass, Kevlar (ZTZ), Nomex (ZTZ), that is, heat-resistant fiber made from aramid polyamides, for example, twisted and interlaced in various ways, as well as paper , multilayer glued paper, melamine (ZTZ) and various synthetic plastic films with high modules, such as milar (ZTZ), captan (ZTZ) plastics based on polycarbonates, phenols, polyesters or similar plastics, plastics, armies fibers, etc., and metal sheet material or foil. Studies of liquid crystalline polymer thermoplastics show that they can be successfully used for injection molding, to obtain ultra-thin layers or shells of small size, for example, up to 30 cm in diameter. This material itself forms an oriented crystalline structure in the casting direction and preferred orientation for good transmission of sound wave energy from the send point to the panel perimeter.

In addition, this type of casting for this type of thermoplastics and for their other types allows using casting equipment to provide recording signs, such as grooves or rings, for the precise placement of the transducer parts, for example, a drive and a magnetic suspension. In addition, when using weaker core materials, it is believed that it would be appropriate in places to increase the thickness of the outer layer, for example, in the annular space zone, to 150% of the diameter of the transducer in order to reinforce this zone and it is preferable to add vibration energy to the panel. Thus, with the help of softer foams, the amplitude-high-frequency characteristic will be improved.

Materials intended to form the core layer include fabricated honeycomb structures or corrugated structures of aluminum alloy sheet or foil, Kevlar (ZTZ), Nomex (ZTZ), plain paper or laminated paper and various synthetic plastic films, as well as foams, or cellulosic materials, even aerogel metals, if they have a suitable low density. Some materials suitable for the core layer themselves are able to form their shell during manufacture and / or in another case have sufficient bending stiffness without the formation of a layered structure between the two outer layers. Such a high performance cellular material is known as Rohacell (ZTZ), and may be suitable for manufacturing a radiation source panel without outer layers. From a practical point of view, the goal is to provide overall lightness and rigidity, in particular, to achieve optimal core and outer layers and transitions between them.

Some of the preferred panel formulations have outer layers of metal or a metal alloy, or alternatively, carbon fiber reinforcing material. Both the one and the other, as well as designs that use an airgel alloy core or a honeycomb metal core structure, will have significant radio frequency shielding properties, which are essential in some cases to ensure electromagnetic compatibility. Conventional loudspeakers, panel or conical, do not have their inherent shielding ability to ensure electromagnetic compatibility.

In addition, the preferred types of piezoelectric and electrodynamic transducers have negligible electromagnetic radiation or magnetic scattering fields. Conventional loudspeakers have a large magnetic field extending to a distance of 1 m unless special measures are used for shielding.

If it is important to maintain shielding, you can make electrical connections to the electrically conductive parts of the corresponding panel, or you can use electrically conductive foam or a similar boundary layer to set the edges.

Suspension (3) can dampen or reduce the amplitude of vibrations of the edges of the panel (2), preventing excessive movement of the panel in the edges. In addition, as an alternative, additional damping means may be used, for example, pads glued to the panel at selected locations to absorb or damp excess movement so that the resonance is evenly distributed across the panel. The pads may be those commonly used in conventional speaker housings, or may be made of resilient or rigid polymeric sheet material. Some materials, especially paper and paperboard, and some types of core may have self-damping properties. If necessary, it is possible to envisage an increase in the damping effect in the manufacture of panels using adhesive compositions that provide bonding in an elastic rather than solid state.

Effective damping involves the use of permanent, dedicated means for this in the panel and its sheet material. Edges and corners are of particular importance for the main mode of vibration and the less scattered low-frequency mode of vibration in the panels. The fastening of damping means along the edges of the panel is advisable, since its specified sheet material is entirely enclosed in a frame, although their angles can often be relatively free, for example, to increase the range in the low-frequency region. Fastening can be done with adhesive or self-adhesive materials. Other types of damping, especially for weaker impacts and / or mid and high frequencies, can be achieved with a suitable mass or masses fixed on the sheet material at predetermined calculated locations in the indicated area.

The acoustic panel described above works in two directions. Sound energy emanating from the rear does not have any strong phase dependence on sound energy emanating from the front. Therefore, there are advantages in summing the acoustic power in the room, obtaining sound energy with a uniform distribution of frequencies, reducing the effect of the reflected and standing waves, excellent reproduction of natural space and surroundings in reproduced sound recordings.

Since the radiation from the acoustic panel is largely non-directional, the phase dependence of the signal increases with an offset from the axis. To improve focusing of the stray stereo effect, the location of the speakers, like pictures, at the height of a standing person gives the advantage of a moderate offset from the axis for the sitting listener, which optimally improves the stereo effect. Similarly, a triangular left / right geometric shape relative to the position of the listener provides an additional angular component. Therefore, you can get a stereo effect of good quality.

For a group of listeners, an additional advantage is provided compared to playback from a conventional speaker. The scattered nature of the sound radiation inherent in an acoustic panel gives a volume level of sound that does not obey the law of inverse squares as the distance from a source located at an equivalent point increases. Since the decrease in intensity with a distance is much smaller than that determined by the law of inverse squares, therefore, the intense field of the panel speaker provides an excellent stereo effect for listeners who are in disadvantageous places, compared with the capabilities of ordinary speakers. This is because the listener, who is not in the center, is not affected by the signal from the nearest speaker and caused, firstly, by an excessive increase in the volume of the nearest speaker, and secondly, respectively, by a decrease in the volume of the more distant speaker.

The advantage is also that the loudspeaker is a flat, lightweight panel with an attractive appearance, with good quality sound, where only one transducer is needed and no crossover is needed to separate the spectrum of the audio signal to ensure the full range of sound from each aperture of the panel.

In FIG. 3 shows a distributed mode panel (2) according to the present invention, for example of the type shown in FIG. 1 and 2, intended for use both as a speaker and as a sound receiver or microphone, for example, for use in an interactive environment. Although not shown in FIG. 3, but it is assumed that the panel (2) is installed in the surrounding frame (1) and is attached to the frame by means of an elastic suspension (3) in the manner shown in FIG. 1 and 2. The frame is suspended using a pair of cables (33), for example, to a ceiling or a rack mounted on the floor (not shown).

A resonance is excited in the panel and an acoustic signal propagates by means of a transducer (9) of the type described in international applications No. WO 97/09859, WO 97/09861, WO 97/09858, which, in turn, is connected to an amplifier (10) and controlled by it.

The panel also has two indicated second transducers (63) of oscillations, which can be performed by piezoelectric transducers of the type shown in Fig. 4, which are connected in parallel and provide a signal to the receiver and signal former (65) connected to the output (66 ) An additional transducer (63) of oscillations mounted on the panel (2), which is a transducer, for example, of the type shown in Fig. 4, directly provides a signal to the filter / correlator (64), the output signal of which is supplied to the receiver and shaper ( 65) signal to provide signal correction.

In FIG. 4 shows a transducer (9) for a distributed mode panel (2) made in the form of a crystalline disk-shaped bending piezoelectric element (27) mounted on a disk (118), for example, of brass, which is glued to the surface of the panel (2), for example, by adhesive bond (twenty). During operation, the acoustic signal supplied to the transducer (9) through the terminals (28) causes the piezodisc (27) to bend and thus cause local elastic deformation of the panel (2), thus informing the panel of bending vibrations.

Industrial applicability

In accordance with the invention, a simple microphone loudspeaker is thus provided, for example for use in an interactive environment.

Claims (5)

CLAIM 1. A loudspeaker, made in the form of a panel and containing a distributed-mode acoustic emitter with a transducer, exciting bending vibrations in the emitter, which cause a resonance in the emitter, with at least one additional transducer installed on the emitter, which produces a signal in response to resonance the specified emitter caused by acoustic energy incident on the specified emitter. 2. The loudspeaker under item 1, characterized in that the emitter is installed in the surrounding frame with an elastic suspension. 3. The loudspeaker according to claim 1 or 2, characterized in that the radiator comprises a rigid, lightweight panel with a cellular core enclosed between the outer layers. 4. The loudspeaker according to claims 1-3, characterized in that it contains a transducer (63) mounted on said emitter and generating a signal in response to the resonance of said emitter caused by acoustic energy incident on said emitter and also means for comparing the signal produced by the specified transducer (63), with a signal generated by the specified additional transducer or transducers. 5. The loudspeaker according to claim 4, wherein the comparison means comprises a receiver and a signal conditioner and a signal output means.