CN1554209A - speaker - Google Patents

Abstract

A loudspeaker comprising a panel-form acoustic member adapted for operation as a bending wave radiator and an electrodynamic moving coil transducer having a voice coil mounted to the acoustic member to excite bending wave vibration in the acoustic member. The junction between the voice coil and the acoustic member is of sufficient length in relation to the size of the acoustic member to represent a line drive such that the acoustic member has a mechanical impedance which has a rising trend with bending wave frequency.

Description

speaker

technical field

The present invention relates to a bending wave panel loudspeaker, such as the resonant bending wave panel loudspeaker of the type exemplified by WO 97/09842, and to a drive motor for such a loudspeaker.

Background technique

In the manufacture of vibration transducers for electro-bending wave panel loudspeakers, i.e. moving coils, the size and mass of voice coils currently being considered are directed towards the use of small diameter and low mass voice coil systems, typically tweeters for known piston speakers The size of the coil. In some applications, such as WO 98/39947 to drive bending wave panels or diaphragms, which are driven, for example, from the center so they can act both pistonically and flexibly, such small diameter voice coils can result in power handling and offset-related issues.

For such small diameter voice coils, the driving point impedance (Zm) approximates a panel driven at a single point. Zm vibrates as a modal structure as the frequency increases, but is constant on average and approximates the infinite panel value given by:

$\mathrm{<span\; class="notranslate">\; Zm</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 8</span>}\sqrt{\mathrm{<span\; class="notranslate">\; B\&mu;</span>}}$

A given voice coil mass (Mc) results in a high frequency limit (f(b)) above which the rising impedance of this mass exceeds the constant driving point impedance. This frequency is as follows:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; b</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="Zm"\; filenames="A0181732800151.png,A0181732800152.png"\; state="\{\{state\}\}">Zm</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;Mc</span>}}$

The quality of the voice coil on a known curved corrugated plate is therefore kept at a low value according to the above formula.

The obvious way is to increase Zm or decrease Mc to keep the turnover frequency high in this sound band. The voice coil diameter was only ever slightly increased, and then only to the cap of the unit was found, drum mode, where the resonance became dominant, causing premature roll-off.

Other factors that would work against a low quality voice coil for a piston driven panel are sensitivity and bandwidth. In order to maintain a desired low frequency bandwidth in an ideally closed volume, the diaphragm quality needs to be increased. To maintain high sensitivity, the B1 power factor will need to be high. A high B1 driver generally increases the B1 product by the number of turns, thus increasing the voice coil mass.

Another direction is to use a drop-in vibration exciter design that increases the B1 product from the magnet to keep the voice coil mass low. This has been tracked using a 25mm voice coil diameter with increased stiffness at the drive point. However, power handling and excursion are still limited.

WO 97/09842 is known to provide a flat panel loudspeaker which is pistonically operated at low frequencies and resonant at high frequencies. It is also known that patent US-A-4,532,383 provides a loudspeaker with a moving coil transducer and diaphragm, which are of similar diameter, and the voice coil is configured to drive the diaphragm around it.

Contents of the invention

According to the present invention, there is provided a loudspeaker comprising a panel-form sound element acting as a bending wave radiator, and an electrically moving coil transducer having a voice coil mounted to the sound element for movement in the sound element. Bending wave vibrations are excited in an acoustic component, wherein the interface between the voice coil and the acoustic component has sufficient length relative to the dimensions of the acoustic component to represent a line driver such that the acoustic component has a mechanical impedance whose average increases with bending wave frequency. The junction of the voice coil and the diaphragm can be circular, and the junction can be substantially continuous.

A voice coil junction of sufficient length in this context is one in which the length, or its diameter in the case of a circular junction, is equal to at least one of the parts of the sound component defined by the junction or surrounded by the voice coil The length of the bending wave and is at the highest operating frequency of the speaker.

The mechanical impedance of a panel is equal to the ratio of the force applied at a single point to the velocity obtained at that point. Where the panel is driven by a force acting on a line, the effective mechanical impedance is the ratio of the total force applied on the line to the resulting velocity averaged over the length of the line. In this description and claims, the use of the term mechanical impedance is used to describe this ratio of two drive configurations.

It will be appreciated that for a point driven plate or diaphragm it is just an infinite diaphragm with a truly constant Zm. A finite diaphragm has a Zm that oscillates about the value of the infinite diaphragm. Similarly, the mechanical impedance seen by a large area voice coil on the diaphragm will vibrate as a modal structure, but will rise on average with frequency.

The portion of the sound assembly surrounded by the voice coil may have a different thickness than the portion of the sound assembly outside the voice coil.

The transducer can be configured to simultaneously move the acoustic component in bulk bulk mode and apply bending wave energy to the acoustic component. The size, shape and position of the interface between the voice coil and the sound component can be adjusted relative to the modal distribution of the diaphragm or sound component to achieve a smooth transition from overall motion at low frequencies to higher frequencies resonant bending wave behavior. For example, in the case of a circular diaphragm, normally driven, the second resonance can cause irregularities in the output. With a circular drive wire, the effective perimeter of the drive wire can be positioned and sized to be at or close to the nodal circle of the second resonance. In this context, the first resonance is the bulk or piston equivalent resonance. By coupling to or approaching the nodal circle of this second resonance, its effect is reduced and the mode is driven weakly or not at all. Therefore the designer can adjust the drive parameters to increase the second quality from the low piston frequency to the mode-dense region of the mid-frequency.

Mass bearing may be applied to the sound assembly within the diameter of the voice coil. The acoustic component may be non-circular in shape. The transducer voice coil is co-centered with the geometric center of the sound assembly.

A second transducer may be coupled to the acoustic component within the portion thereof surrounded by the voice coil and used to cause high frequency bending wave activity in that portion. The second transducer may be offset from the main axis of the voice coil.

Coupling means may be used to secure the voice coil to the sound assembly, the coupling means having a non-circular shaped footprint.

The portion of the sound assembly surrounded by the voice coil may be stiffer than the portion of the sound assembly outside the voice coil. The bending stiffness of the acoustic component may be anisotropic. The sound assembly can be bent or dented, or otherwise formed to increase its bending rigidity.

The loudspeaker may include a frame having a portion surrounding the sound assembly and another portion supporting the electrodynamic transducer, and may include means connected between the sound assembly and the frame portion and elastically suspending the The sound component is on this frame. The suspension device may be connected between the frame and the border of the sound assembly. The elastic suspension can be used to mass-carry the sound assembly. The elastic suspension can be used to dampen the acoustic assembly. The elastic suspension may be at least partially formed by the skin of the sound radiator.

The acoustic component may be radiated from the front side of the acoustic energy and may include acoustic masking means disposed on the portion of the acoustical component surrounded by the voice coil, the masking means defining an acoustic cavity.

The electrically moving coil transducer can be offset from the geometric center of the acoustic component and provide an inverse balance mass on the acoustic component.

Action of the large-area voice coil on the diaphragm can produce a distribution of excited modes that results in significant transmission on the radiation axis, at least over some frequency ranges. In some applications, such as differentiation of the output sound, this is beneficial, but in some applications, off-axis power is required. One way to improve off-axis power is to excite the panel in bending wave vibration at a frequency close to or greater than this coincidence frequency.

The coincidence frequency is the frequency at which the bending wave speed in the plate is equal to the speed of sound in air. Above this frequency, the velocity in the plate exceeds the velocity in air, and the ultrasonic vibrations cause strongly directional off-axis radiation. In fact at this coincident frequency the radiation is transmitted directly off-axis, with the transmission angle shifting closer to the on-axis direction as the frequency increases. The coincidence frequency of a flat plate is determined by its bending stiffness (B) and mass density (mu). These parameters can be varied such that the narrowing of the radiation pattern caused by the large area voice coil is at least to some extent compensated by the extra energy delivered off-axis by the bending wave vibration above the coincidence frequency.

The loudspeaker of the present invention can be used as a whole range of devices.

Description of drawings

The invention will be illustrated graphically by way of example in the accompanying drawings, in which:

Figure 1 shows a front view of a speaker driver motor;

Figure 2 is a cross-sectional side view of the drive motor of Figure 1;

Figure 3 shows a front view of a loudspeaker housing;

Figure 4 shows a side view of the loudspeaker housing;

Figure 5 shows a frequency response;

Figure 6 shows the bass frequency response close to the field;

Figures 7 to 9 show front views of embodiments of the diaphragm, each with a supplementary vibration exciter;

Figures 10 to 13 show front views of further embodiments of the diaphragm;

Figure 14 is a perspective view of a further embodiment of a diaphragm;

Figures 15 to 18 show cross-sectional views of specific embodiments of the membrane;

Figures 19 to 21 show cross-sections of specific embodiments of membrane wrapping or suspension;

Figure 22 is a cross-sectional view of an embodiment of a speaker drive motor;

Figure 23 is a front view of an embodiment of a diaphragm;

Figure 24 is a cross-sectional view of an embodiment of a diaphragm;

Figure 25 is a polar diagram comparing the responses of a known pistonic loudspeaker and the loudspeaker of the present invention; and

26 and 27 are front views of further embodiments of a voice coil/diaphragm wire-actuated interface.

Detailed ways

Shown in Figures 1 and 2 is a loudspeaker drive motor 1 intended to be mounted to an acoustic panel, such as in an enclosure, see Figures 3 and 4 below, comprising a circular planar diaphragm of rigid lightweight material, such as Consisting of a core sandwiched between skins of high tensile sheet material, which form an acoustic component or radiator for simultaneous pistoning, and flexing to operate at higher frequency bending wave resonance devices. In this way, the drive motor of the present invention is able to operate as a full-range device which essentially covers the entire sound spectrum with a wide sound dispersion, unlike known piston drives whose frequency band or at least their dispersion angle is at high frequencies Limited by the diaphragm diameter, see Figure 25 below, and a bending wave driver stops at frequencies below 200 Hz unless a very large diaphragm size.

In general, the diaphragm 2 is supported in a known manner by a frame or basket 3, for example made of metal, forming an annular flange 4 at its front end, which has several spaced fixing holes 5, whereby the frame can be fixed In a suitable hollow speaker enclosure, please refer to Figures 3 and 4 below. A corrugated suspension 6, for example of rubber-like material, is fixed by an adhesive to the membrane around its perimeter, and the suspension can be clamped to the annular flange 4 with the help of a clamping ring 7 , whereby the diaphragm is pistonically movable relative to the frame.

The frame may support an electrically movable coil transducer 8 for pistonically moving the diaphragm and for applying bending wave energy to the diaphragm to cause it to resonate, for example in the manner described in WO 97/09842. The transducer comprises a magnet assembly 9 fixed to the frame and defining an annular gap 10 concentric with the diaphragm, in which a voice coil and combination 11 of the former is mounted for axial movement, It is then fixed concentrically to the diaphragm by means of a coupling ring 12 . In a commonly known manner, a wave suspension tripod 13 is fixed between the voice coil assembly and the frame to ensure proper axial movement of the voice coil in the annular gap.

The voice coil diameter is large relative to the bending wave length, and the effect is a line driver to the diaphragm, rather than a point driver, which typically has small diameter voice coils for bending wave radiators using electrokinetic exciters. This line driver provides a significant increase in the mechanical drive impedance to the voice coil, and this higher mechanical impedance allows the system to tolerate relatively high quality voice coils without prematurely stopping at high frequencies. Also, because of the large diameter of the voice coil, it is possible to manipulate the diaphragm panel stiffness to allow the portion of the diaphragm surrounded by the voice coil to have multiple modes, rather than a single dominant drum mode, as small diameter voice wires have. The inner portion 16 of the diaphragm may be surrounded by the voice coil, as shown in Figure 1, while the outer portion 17 of the diaphragm extends radially beyond the voice coil.

As shown in Figures 1 and 2, small masses 14, 15 are fixed to the diaphragm within the diameter of the voice coil to adjust and/or smooth the frequency response of the sound radiator. This quality is not always necessary, but often is. These masses appear as dispersed masses, but do not have to be dispersed. Its mass may range from 0.5 g to 100 g, substantially in the range of 2 to 20 g. It can provide one or more of these qualities.

The loudspeaker driver embodiment of Figures 1 and 2 has been optimized for use with a hi-fi loudspeaker which, when coupled to an amplifier, has a planar voltage conversion function throughout the sound band. As part of the design criteria for this embodiment, the following design parameters may apply.

The transducer has a large 75mm diameter voice coil mounted in a low inductance motor system with a vent 18 having a copper eddy current shield 19 on the pole piece or front plate 20 . FIG. 2 shows a cross-section of a neodymium magnetic ring 21 installed in the center of a magnet circuit, which includes a magnetic cup 22 and the front plate 20, resulting in an average B field of 0.8T. The voice coil 11 protrudes from the magnetic front plate 20 to form a protruding structure. The voice coil consists of an aluminum winding with a height of 14.5 mm wound on a 0.1 mm thick aluminum former. The voice coil parameters are as follows:

Mandrel or bobbin diameter = 75mm

Number of Coil Layers = 2

Wire diameter = 0.3mm

Number of turns = 71

The coupling ring 12 is used to provide a fixed interface between the voice coil and the diaphragm. This overlap is inside the voice coil. It provides a 2.5mm overlap to allow a good bonding area between the coupler and the voice coil former. The coupling loop extends the effective length of the voice coil by 1.7mm, providing a loop width of 3.5mm to couple to the diaphragm. This is shown in Figure 2. The material of the coupling ring is commercial grade thermoplastic or thermosetting resin, such as ABS, and its mass is 3.4g. For the bond between the voice coil and the coupler, a heat resistant cyanoacrylate (Loctite 4212) is used. This is also used to bond the coupler to the diaphragm.

The dynamic parameters of the motor system with the coupling loop are shown below:

Mms=11g (moving mass of the voice coil combination)

Rms＝1.95Ns/m (mechanical impedance of suspension)

B1＝8.1Tm (motor conversion factor)

Re＝6.5ohm (DC resistance of voice coil)

Fs＝40Hz (mass spring resonance of the system)

Le=0.2mH (the inductance factor of the voice coil at 1kHz)

The diaphragm materials used and their parameters are as follows:

Material = Rotrex Lite 51LS (trade name) 3.5mm (3.5mm thick 511S grade uncompressed Rohacell (trade name) core solid closed cell polymethacrylimide thermoplastic foam with a glass curtain/thermoplastic skin). Diameter = 120mm.

    Parameter series are listed in Table 1

Table 1 mass area density m 0.35 Kg/ ^m2 Poisson ratio N 0.11 bending rigidity D1 2.4 N m bending rigidity D2 1.8 N m Damping D D. 0.02 in-plane shear rate Shr 0.36 thickness T 3.5mm m Shear modulus Gz 19M Pa Damping Gz D. 1 coincidence frequency Fc 7.7 kHz

From the parameters provided in Table 1, the wavelength of the panel can be calculated at the highest operating frequency, ie 20kHz. This calculation is based on an average bending stiffness of 2.1Nm for a wavelength of 28mm. The voice coil diameter is therefore 2.7 times the wavelength of the highest frequency of operation. In prior art bending wave loudspeakers, the first cavity resonance corresponds to half the wavelength of the voice coil.

The coincident vanes of this panel provide a strong sound output off-axis near or above the coincident frequency, as shown in Table 1 above. 25, where the thin line or trace 45 is the pattern of a loudspeaker according to the invention having a 300 mm diameter diaphragm, and the thick trace 44 is a known 250 mm diameter piston diaphragm.

The frame includes an aluminum back plate 23 to support the transducer 8 , which is connected to the front flange 4 . Allen bolts (not shown) are used to secure the clamp ring 7 to the flange 4 .

A pair of masses 14, 15 fixed to the diaphragm is used to smooth the first tympanic mode of the inner part of the diaphragm, which is at about 2 kHz.

The parameters of the motor drive unit are as follows:

dD=14cm (the diameter of the radiation area (centered on the center of the perimeter))

Mms=27g (moving mass of the voice coil and diaphragm combination)

Rms＝2.4Ns/m (mechanical impedance of suspension)

B1＝8.1Tm (motor conversion factor)

Re＝6.5ohm (DC resistance of voice coil)

Fs=33Hz (mass spring resonance of the system)

Le=0.2mH (the inductance factor of the voice coil at 1kHz)

3 and 4 show the speaker housing 24 of the drive unit of FIGS. 1 and 2 , which has an inclined front side 25 and sides 26 . A cavity 27 is provided on the front side 25 to receive the drive unit or motor 1 . The enclosure has been designed to provide a volume of 17 liters as a maximum flat alignment. The enclosure form is chosen to disrupt the internal enclosure standing waves, although it is not necessary for the design and operation of the loudspeaker. The shell is constructed from 18mm medium density fibreboard (MDF). The joint is glued (using PVA wood glue) and rotated to provide an air seal.

Next, the measurement of the above loudspeaker embodiment is carried out in an anechoic chamber, the microphone is located at 1m (on the axis of the diaphragm), and the output is 2.83v. As shown in FIG. 5, inaccuracies occur for measurements below about 200 Hz, so a near field measurement showing this low frequency performance is shown in FIG.

While the embodiments of Figures 1 and 2 use a single large diameter voice coil driver, a supplemental excitation device can be used to improve the high frequency level and/or extension, and directional performance of the loudspeaker. The supplemental exciter can be placed anywhere on the diaphragm to provide a smaller radiation area. Devices like large-area piezos can be used in the form of small-area or strips, or smaller moving-coil devices. This is shown in Figures 7 to 9. In FIG. 7 , it will be seen that a circular piezoelectric disc vibration exciter 28 has been installed in the center of the diaphragm 2 , and inside the diameter of the voice coil 11 . In the specific embodiment of FIG. 8 , a piezoelectric bar-shaped vibration exciter 29 has been mounted on the diaphragm 2 concentrically with it and located on the inner diameter of the voice coil 11 . In Figure 9, a circular disc vibration exciter 30 has been mounted on the diaphragm 2 inside the voice coil diameter 11, but off-centre.

It can be seen that the voice coil moving mass has little effect on the high frequency extension of the loudspeaker. The invention is therefore not limited to lightweight voice coils. This represents a range of motor systems using moving magnets, and/or relatively high mass coupling loops between the voice coil assembly and the diaphragm, which currently rule out point drive designs for small drive area or bending wave loudspeakers. This may allow complex coupler designs to convert the voice coil loop to other preferred shapes for improved performance. Examples of triangular, square and elliptical shaped coupling rings are shown in Figures 10 to 12, respectively, which are referenced 31 to 33, respectively. These shapes represent the distribution of excited modes and thus the sense of direction. For example, as shown in Figure 13, if a triangular-shaped diaphragm 34 had been chosen, along with a rectangular coupler ring 32 rotated at an angle relative to the side of the diaphragm, it could provide a more unusual mode pattern in the diaphragm. This also further improves the on-axis and off-axis frequency response.

In the specific embodiment of Figures 1 and 2, the voice coil has a diameter of 75mm. This can be increased or decreased according to the design specification. If the design specification requires narrower directivity for differentiation applications, a larger voice coil coupled to a low wave velocity panel, ie with a very high Fc, can be used. Conversely, if wide directivity is required, a smaller voice coil can be used, which is the condition of the line driver. But this requires electrical high frequency pressurization to maintain a constant pressure throughout the sound band.

As shown in FIG. 13 above, the present invention is not limited to the circular panel shape shown in the embodiments of FIGS. 1 and 2 . Other shapes may be preferable for directivity and/or frequency response, since different mode shapes may result from the geometry of the panel. It is possible to expect a more complex mode shape in the panel, so that there is less directionality in the sound output. Examples include square, rectangular, and hexagonal panels.

Also, as shown in Figure 14, the present invention is not limited to pure piston behavior of the diaphragm at low frequencies, and tympanic membrane-like behavior at low frequencies. The membrane 34 can be a large radiant panel. This provides a self-baffle arrangement that provides a bipolar bass response, as indicated by opposing arrows. The panel edge can be free or clamped.

The invention is not limited to a planar membrane or to a single material form. The profile and shape of the diaphragm can be used to alter the modal behavior. For example, the portion of the diaphragm surrounded by the voice coil could be constructed of a different material, or use the same material but be thicker or thinner. Exemplary embodiments are shown in Figures 15-18. Rigidity can be imparted to the diaphragm by contouring. Stiffness variation can also be achieved using material isotropy. Thus in FIG. 15 the inner part 16 of the membrane 2 is thinned by indenting its lower skin. In Fig. 16, the inner part 16 of the membrane is thickened. In Figure 17, the inner portion 16 of the membrane 2 is uniformly thinner than the outer portion 17 of the membrane. In FIG. 18 , the outer part 17 of the membrane 2 tapers in thickness towards the inner part as far as the left side of the drawing and forms a curved profile of varying thickness as can be seen from the right side of the drawing.

It can be seen that the diaphragm surround affects the sound performance. Both the piston and the modal area can be varied by changing the material properties of the surround. In particular, high frequency performance can be improved if mass is applied to the perimeter of the diaphragm, as indicated at 36 in FIG. 19 . The edge damping of the diaphragm can be used to control its modal behavior. This may be in the form of surface treatment or edge ratio damping, which may pass through the surrounding footprint, as shown at 37 in FIG. 20 . The panel skin, or one of them, may be used to form the surround, as shown in FIG. 21 . In this embodiment, the membrane comprises a core 38, and skins 39, 40 covering the core. The lower skin 40 is extended to form the surround or suspension 6 . This may provide cost benefits. Benefits may also include low loss termination of the diaphragm.

Radiation at frequencies near and above the coincidence frequency (fc) is used in the preferred embodiment to broaden the directivity at high frequencies. However, coincidence can be set at either end of the spectrum. Increasing the panel stiffness/reducing the coincidence frequency should still provide wider directivity and improve modal region sensitivity.

Using an isotropic diaphragm, for example at about twice the Fc, will provide side vanes at the same position in both planes. When using anisotropic panels, coincidence can be set independently in spaced planes to provide a smoother overall power response.

A mechanical element, such as a mass or voice coil coupled to the panel, may provide a mechanical filtering device. The frequency response can be modified by placing an interface between the voice coil coupler and the panel. Electrical shelving of passive components or amplifier switching function shelving/high frequency boosting can also be used to modify the sound output of the device.

In the particular embodiment of Figures 1 and 2, coherent sound is radiated by the annular region in which the voice coil is fixed to the diaphragm. This can cause transmission at high frequencies due to the large radiation area relative to the wavelength in air. As shown in Figure 22, in order to widen the directivity at high frequencies, a mask 41 with a small cavity 42 can be placed over the inner part 16 of the diaphragm 2 on a support 43 mounted on the frame 3 to This translates to a smaller radiation area. This effect has been seen when measuring from the rear of the device. In the embodiment of Figures 1 and 2, the exhaust port 18 in the motor system forms the shroud cavity, which allows for post-radiation.

If desired, as shown in Figure 23, the voice coil 11 can be placed at an off-centre position on the diaphragm 2 to improve the distribution of the resonant modes excited in the diaphragm, which has a counter-balance mass 35 placed on the diaphragm to Protect against vibration.

As shown in Figure 24, the diaphragm 2 need not be flat and may be recessed or otherwise formed to increase its rigidity. This can take the form of a changing curvature across the membrane, so the stiffness becomes greater towards the edges of the membrane, as shown. The curvature or contouring of the diaphragm can assist in scaling the diaphragm while keeping fc fixed and facilitate smoothing the piston for mode transitions, especially for larger diaphragms.

In Fig. 26, it shows a circular diaphragm 2, which is driven by the voice coil of a transducer, not shown, which has a coupler 46 made of a straight line, which is identical to that of Fig. 1 and The coupler ring 12 of the specific embodiment of 2 is connected between the voice coil and the diaphragm to provide a linear drive interface. The coupler 46 is arranged and disposed on a diameter of the diaphragm with its ends equally spaced from opposite edges of the diaphragm.

In Fig. 27, which shows a rectangular diaphragm 2 driven by the voice coil of a transducer, which is not shown, it has a coupler 46 formed of a line connected between the voice coil and the diaphragm to provide a constant Line driver interface. The coupler 46 is positioned off-center to the diaphragm and at an angle relative to the sides of the diaphragm.

Industrial applicability

The present invention thus provides an efficient way to increase the frequency bandwidth of a bending wave loudspeaker.

Claims (24)

1. A loudspeaker comprising an acoustic component in the form of a flat plate for use as a bending wave radiator and an electrically moving coil transducer having a voice coil mounted to the acoustic component to excite the Bending wave vibration, wherein the interface between the voice coil and the sound component has a sufficient length relative to the size of the sound component to represent a line driver, such that the sound component has a mechanical impedance that varies with the bending wave frequency an upward trend. 2. The speaker as claimed in claim 1, wherein the interface between the voice coil and the sound component is circular. 3. The loudspeaker as claimed in claim 1 or 2, wherein the interface between the voice coil and the acoustic component is substantially continuous. 4. A loudspeaker as claimed in claim 2 or 3, wherein the part of the sound assembly surrounded by the voice coil has a different stiffness than the part of the sound assembly outside the voice coil. 5. A loudspeaker as claimed in any preceding claim, wherein the acoustic component is also movable in bulk mode by the transducer. 6. A loudspeaker as claimed in any one of claims 2 to 5, comprising means for enclosing a mass to the sound component within the diameter of the voice coil. 7. A loudspeaker as claimed in any preceding claim, wherein the acoustic element is non-circular in shape. 8. A loudspeaker as claimed in any preceding claim, wherein the transducer voice coil is concentric with the geometric center of the sound assembly. 9. A loudspeaker as claimed in any one of the preceding claims, comprising a second transducer coupled to the acoustic component in the portion thereof surrounded by the voice coil, and for causing high frequency in that portion Bending wave activity. 10. The loudspeaker of claim 9, wherein the second transducer is offset from the axis of the voice coil. 11. A loudspeaker as claimed in any preceding claim, comprising coupling means for attaching the voice coil to the sound assembly, the coupling means having a non-circular shaped footprint. 12. A loudspeaker as claimed in any preceding claim, wherein the portion of the acoustic assembly surrounded by the voice coil is stiffer than the portion of the acoustic assembly outside the voice coil. 13. A loudspeaker as claimed in any preceding claim, wherein the bending stiffness of the acoustic assembly is anisotropic. 14. A loudspeaker as claimed in any one of the preceding claims, comprising a frame part of which surrounds the sound assembly and part of which supports the electrodynamic transducer and which comprises a frame for attachment between the sound assembly and the sound assembly. means between the frame sections and elastically suspends the sound assembly from the frame. 15. A loudspeaker as claimed in claim 14, wherein the suspension means is connected between the frame and the edge of the sound assembly. 16. A loudspeaker as claimed in claim 14 or 15, wherein the elastic suspension is used to incorporate mass into the sound assembly. 17. A loudspeaker as claimed in any one of claims 14-16, wherein the elastic suspension is used to dampen the acoustic assembly. 18. A loudspeaker as claimed in any one of claims 14-17, wherein the elastic suspension is at least partly formed by a skin of the sound radiator. 19. A loudspeaker as claimed in any preceding claim, wherein the sound assembly has a front side from which sound energy is radiated and includes sound masking means positioned between the portion of the sound assembly surrounded by the voice coil above, the masking device defines an acoustic cavity. 20. A loudspeaker as claimed in any preceding claim, wherein the electrodynamically moving coil transducer is offset from the geometric center of the sound element and comprises a counterbalanced mass on the sound element. 21. A loudspeaker as claimed in any preceding claim, for use as a full range device. 22. A loudspeaker as claimed in any preceding claim, wherein the sound assembly is dented or otherwise shaped to increase its rigidity. 23. A loudspeaker as claimed in any preceding claim, wherein the arrangement is such that the acoustic component is excited by bending wave vibrations at a frequency close to or greater than the coincidence frequency. 24. The loudspeaker as claimed in any one of the preceding claims, wherein the size, shape or position of the interface between the voice coil and the acoustic component is configured relative to the modal distribution of the acoustic component to achieve Smooth transition to resonant bending wave behavior at higher frequencies.

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