HUP0002652A2 - Acoustic device - Google Patents

Abstract

The object of the invention is an acoustic device, which contains an element that is transversely extended compared to its thickness and capable of sustaining bending waves causing an acoustic effect in the operating acoustic frequency range through the spatial distribution of resonant modes of natural bending wave vibrations on its surface, where the bending stiffness of the element changes along its surface, and this element is more favorable to the spatial distribution of resonant modes for the acoustic effect does, and the center of bending stiffness of the element is shifted from the geometric center of the element. HE

Description

DANUBIA 90398-8071

Technical area.

ACOUSTIC DEVICE

PUBLICATION COPY

The invention relates to the field of acoustic devices, which are suitable for producing an acoustic effect by means of bending waves and are typically (but not exclusively) used in or as loudspeakers.

State of the art

The specification of the international patent application published under the reference WO-A-97/09842 contains general teachings on the nature, structure and design of acoustic panel elements capable of storing and transmitting applied vibration energy in the form of bending waves, which panel elements store and transmit bending waves in an acoustically active area or areas, which areas are transverse to the thickness, usually extending to the edge of the element or elements (if not necessary). The teachings of the given subject matter include the analysis of typical panel shapes where the bending stiffness is directionally anisotropic or not across or along said area and thereby the resonant mode vibration components are distributed in said area(s), which is advantageous from the point of view of acoustic coupling with the surrounding air; and in order to designate a definable location or locations within said area or areas for an acoustic transducer device or devices, in particular for an operationally active or moving part or parts thereof, which exerts an effect on acoustic vibrational activity in said area or areas, and in relation to associated signals, which are usually electrical and correspond to the acoustic content of such vibrational activity. The international application referred to in this application further describes such elements as "passive" elements or in passive elements, i.e. without transducer means, for example for echo cancellation, or for acoustic filtering, or for acoustic sounding of a space or a room; or as an active acoustic device or device comprising a bending wave transducer means, and this includes a fairly wide range of loudspeakers as sound sources, which are

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- 2 They are fed with an input signal to be converted into sound, but can be used, for example, as a microphone or in microphones that are exposed to a sound effect to be converted into a different signal.

Our pending UK patent application (P.5840) relates to the use of mechanical impedance characteristics to refine the geometry and/or location or position of transducer means of an acoustic device of such panel elements used as or in an acoustic device. The contents of this UK patent application and the previously referenced international patent application are hereby incorporated by reference into this application insofar as they are applicable to the explanation, understanding or definition of the present invention.

This invention relates in particular to active acoustic devices in the form of loudspeakers using panel elements, which devices generally operate as described above (and which may be referred to as distributed mode acoustic radiators/resonant panels, as referred to hereinafter), and which particularly advantageously allow a satisfactory combination of the piston effect with the bending wave effect. However, more general or broader aspects of the invention will become apparent from the following.

Disclosure of the invention

In a first aspect, the invention relates to active acoustic devices operating by means of a bending wave in a panel element, in particular by enabling an effective placement of the bending wave transducer device which differs from the teaching of the above-referenced international and UK patent applications, i.e. this placement is different from the placement resulting from the analysis and preference known from the international patent application, including even placement at the center of mass and/or geometric center instead of a location at a distance therefrom.

From a second aspect, the solution according to the invention relates to acoustic devices based on the bending wave effect arising in panel elements, in particular by implementing an effective distribution of the resonant mode vibration.

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- 3 in relation to which may differ from that which results from the characteristic teachings and preferences of the above international and UK patent applications, even if they have the same arrangement or geometry.

In a third aspect, the invention relates to acoustic devices based on bending waves generated in panel elements, in particular by implementing the resonant mode vibration in panel elements in an efficient distribution, the design or geometry of which panel elements differs from that which is considered to be substantially advantageous in the characteristic teaching and preference of the above international and UK patent application.

It is useful to note that effective and characteristic embodiments of the solution according to the invention employ panel element(s) which internally enable the spatial distribution of resonant mode vibration components effective in terms of acoustic performance, which is essentially the same or similar to the solutions according to the above international and UK patent applications, and are essentially based on the simple excitation of such internally spatially distributed acoustic bending wave effect, and thereby achieve successful acoustic operation, rather than in any other way implementing similar conditions piece by piece in the panel element(s) for the intentional alteration of other acoustic effects, namely in the case of panel elements for which such internal distributed resonant mode effect is not even a design condition, for which other characteristic structural or other conditions must usually be implemented, for use in other frequency ranges and/or for the selective suppression of vibrations specifically generated/pinned in the panel element, which is not internally effective as described above. international and UK patent applications, in the present case, where it is typically substantially unsuitable due to the geometry and/or position of the transducer element.

The effective method and means of the invention include changing the stiffness distribution in at least one area or areas of such panel element or elements that are acoustically active for the desired acoustic performance and bending wave effect. As

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- 4 it will become clear later, such a change can be usefully and directly related to the effective removal of the transducer means from a position as taught in the referenced international and UK patent applications to a different location or locations according to the invention and/or compared to such patent applications in order to make the unfavourable configurations or geometric properties of the panel elements more similar to favourable configurations or geometries from the point of view of acoustic operation, involving the spatial distribution of the resonant mode, which includes the spatial distribution of the resonant modes of vibration resulting from the bending wave operation and/or the resonant mode distribution which is at least to some extent different, either simply as a consequence of the different or varying spatial distribution of the bending stiffness, or depending on the subsequent different location or locations of the transducer means, or both.

The above-referenced international patent application relates to a panel element or elements formed with different bending stiffnesses, in which the bending stiffness varies in different directions along the intended acoustically active area or areas, which active area may extend over the entire area or areas of the panel element or elements, or a smaller area, in a direction relative to two coordinates or in such a direction resolvable, and substantially constant therethrough. In contrast, the bending stiffness or stiffnesses of the preferred panel element or elements according to embodiments of the present invention vary in some directions or in some direction of said area or areas and this variation is not resolvable to constancy in perpendicular coordinates or in any other direction or directions.

The spatial variation of the bending stiffness can of course be easily achieved by varying the thickness of the acoustic panel element, however, other possibilities also arise, for example in the case of sandwich structure designs and/or in relation to the thickness and/or density of monolithic structures made of composite type materials and/or the tensile strength of the top layer of the sandwich structure.

Although the practically available results do not allow

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- 5 the precise examination and quantitative change and actual areal distribution of the acoustically effective resonant mode vibration in the panel element according to the invention - even in a case where its geometry and/or average stiffness are substantially similar in the relevant directions as in the case of the typical isotropic or anisotropic embodiments of the above international patent application - the performances that can be gleaned from the practical results indicate that there is little, if any, decrease or deterioration in the successful acoustic performance using the bending wave effect, and gives encouragement that there is hope for improvement. However, in the case of the fundamentally favorable design/geometry of the above international and UK patent applications (on the areal distribution of the resonant mode vibration) the beneficial effects can be substantially maintained to a very useful extent, and practically two groups or types of inventive considerations can be put into practice to achieve the above viewpoint.

One group/type has already been anticipated, namely, providing a more convenient or suitable location or locations for the transducer device in or around the acoustically active panel elements, the design or geometry of which panels is known to be advantageous in the isotropic or anisotropic embodiments of the above international and UK patent applications, while at the same time being advantageous in the so-called 'natural' position of the transducer location (as taught in these patent applications).

As already indicated, one group/type typically implements more suitable locations on the acoustic active panel elements or areas thereof for the transducer device, the design or geometry of which panels is known to be advantageous for isotropic and anisotropic implementations in the above-referenced international and UK patent applications, and effectively shifts the so-called natural positions for the transducer device (which locations may be designated in accordance with these patent applications) and shifts this position to different locations on the panel element, namely by making such natural location or locations relatively larger on one side and/or smaller on the other side.

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- 6 is achieved. The region or regions of greater bending stiffness serve to effectively shift such natural location or locations from one side to the other side of such region or regions, typically to the region or regions of lesser bending stiffness, and the region or regions formed with lesser bending stiffness serve to shift such location towards their own region. The other group/species can be considered to include the ability to only partially define at least one imaginary sub-geometry within a larger overall panel element geometry which is not typically conducive to well-distributed mode acoustic operation, as described in the above international and UK patent applications; such sub-geometry is not fully defined and not necessarily characteristically advantageous in itself, but its partial limitation has a significant improving effect on the distributed mode acoustic operation, say, by directing it to a type of design or geometry which is known to have characteristic advantages, unless it at least approximates such a preferred design; such improving effect is particularly relevant to the distributing resonant modes, hence at lower frequencies, but does not necessarily (indeed preferably not) limit the higher frequency bending wave operation and the distribution of the resonant mode on such sub-geometry, i.e. it allows for such higher frequency resonant mode distribution of vibrations which pass beyond and pass by such partial sub-geometry definition.

In order to achieve the required or desired areal distribution of bending stiffness, the panel element or elements may comprise at least a core layer or layers which are first formed with a substantially uniform isotropic or anisotropic structure or structures, for example such as those taught in the above international and UK patent applications, and this includes sandwich structures comprising facings on a core layer or layers. The thickness

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- 7 can then be easily designed to obtain the desired areal distribution of stiffness or stiffnesses. In the case of deformable material or materials, such as foam or foams, such a change in thickness can be achieved by selective compression or deformation and thereby a desired contour can be achieved, for example by the application of controlled heating and pressure, whereby any desired profile can typically be achieved and is easily implemented even after the application of any cover layer (depending on the extensibility of the material forming such cover layer). Another possibility for designing the element is to use local stiffening or weakening, possibly advantageously forming a gradual series of these. For example, in certain suitable complex sandwich structures and continuous cellular or honeycomb structures formed from a mesh of cells extending from one cover layer to another, or rigid, form-retaining, wrinkle-resistant composite materials, thickness variation can be easily achieved by selective peeling to a contour/profile corresponding to the desired thickness. Neither of these options necessarily involves a change in the geometric center, but peeling does change the location of the center of mass much more than wrinkling. Further options for varying the desired thickness/stiffness of the core or cores thus prepared are also discussed, including solutions without changing the center of mass, which may be important for transducer devices that combine piston and bending wave effects, in which case the piston effect is best controlled when centered with respect to the coincident center of mass and geometric center, in order to avoid differential torques resulting from mass distribution and/or unbalanced air pressure effects relative to the transducer location or locations.

The center of mass can of course be simply relocated, typically to the geometric center, by selectively associating a mass or masses to the relevant panel element or elements, preferably without this having unacceptable effects on the desired areal distribution of stiffness, for example masses that are also sufficiently small.

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- 8 so as not to unacceptably influence the low frequency bending wave effect and to effectively decouple from the higher frequency acoustic effect or effects, for example by suitably semi-compliantly installing a small weight or weights in the opening or openings of the panel, which weight or weights are also small enough not to unacceptably influence the acoustic effect or effects.

By increasing the stiffness in one direction away from the natural location or locations of the transducer or by decreasing the stiffness in a substantially opposite direction or towards the other side, a location for the transducer device is obtained which is substantially in said one direction or on said one side, which may preferably be in the direction of the geometric center. Such relative increase/decrease in stiffness may be complex with respect to the resulting contour of the respective panel element, including increased thickness/stiffness tapering towards the edge of the panel and decreased thickness/stiffness increasing upwards, for example in order to make the thickness at the edge of the panel element substantially uniform.

Additionally or alternatively, the inventive nature of at least one group/type is seen in the panel element being suitable for acoustic bending wave operation with a distribution of bending stiffness in its acoustically active area which is in no sense co-centered with the center of mass and/or geometric center of the panel element, although the locations or location of the acoustic transducer means or device - whether for bending wave action or piston action or both - may and often advantageously coincide.

At this point, we would like to note that there are two possibilities according to which the spatial distributions of stiffness or stiffnesses in a panel element can be considered or treated as central, one is analogous to the way in which the center of mass is usually determined, i.e. the first moment of stiffness is set to 0 and thus in this sense it corresponds to high stiffness (which is then called

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- 9 is called the high center of stiffness); while the other way is the inverse of this, i.e. the first moment of the reciprocal of the stiffness is made 0 and thus in another sense it corresponds to weakness or low stiffness (hereinafter referred to as the low center of stiffness). In the case of the isotropic or anisotropic panel elements analyzed in detail in the referenced international patent application, these imaginary high and low centers of stiffness (if this makes sense in this context), actually coincide, and also normally coincide with the center of mass and the geometric center, however, in the case of a panel element with distributed stiffness as described herein, these imaginary high and low centers of stiffness are typically spaced apart and typically further from the center of mass and/or the geometric center.

Returning to the imaginary displacement of the practical effective location or locations of the transducer device for the bending wave effect (by means of the preferred distributions of stiffness or stiffnesses described herein) (from the location or locations permitted by the preferred teachings/analysis of the said international and UK patent applications to a location or locations different therefrom) and such displacement can be usefully considered as a displacement towards the low centre of stiffness, thus occurring in the same direction as the desired imaginary displacement and/or a displacement away from the said high centre of stiffness, which can usefully allow at least one structural design reference location to be provided for the variation of the bending stiffness or stiffnesses by means of the desired/required appropriate distribution. The change in bending stiffness from such low center or centers outwards towards the edge or edges of the relevant panel element or elements - where the stiffnesses or stiffnesses typically increase to different degrees and/or increase at different rates in multiple directions, at least towards the high center or centers.

The advantageous structure of sandwich-type panel elements with a honeycomb, cellular core provides the required rigidity.

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- 10 have a distribution of stiffness, due to the contributions made by the individual cell geometries in the as-made version without necessarily having a significant effect or effects on the distribution and the center of mass. Thus, desired areal distributions of stiffness or stiffnesses can be achieved by varying the cells by varying the cross-sectional area (if not the shape), the cell height (effectively the thickness of the core) and the cell wall thickness of any or all of the cells, including such gradations in the applied increase/decrease as is desirable or necessary. Variable bending stiffness(s) can be achieved in such a context without disturbing the mass distribution, for example by varying the cell wall thickness and changing the cell height, with the same nominal cell area, and/or by varying the cell area and/or the cell height with the same cell wall thickness, and of course this can be improved or otherwise influenced by various changes in the top layer, including different numbers and/or properties of the applied layers.

The novelty of the panel elements according to the invention is further represented by the fact that the stiffness or stiffnesses have at least "low centers" and practically the most effective driving location or locations, which are typified in the sense of the minimum and maximum standard deviation of the travel time to one or more edges of the panel for imaginary or actual bending waves, if they are considered to start from the low center of stiffness and the transducer position or positions.

Returning to the second general aspect mentioned earlier, the panel elements described herein, formed with a distribution or distributions of stiffness or stiffnesses (which may be referred to as eccentrically formed), may have the ability to be used to ensure that a panel of a particular given or desired shape (e.g., a desired design or geometry) can in practice exhibit an effective acoustic bending wave effect, which is described in this

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- 11 shapes have not been considered available until now, at least according to the previously applicable proposals; which include not only unfavorable shapes compared to the known favorable shapes, but also shapes not so compared, but which can be treated according to the teachings here, at least in order to approach what has hitherto been characteristic only of certain characteristically favorable shapes.

Indeed, the invention also extends to a physically feasible spatial distribution of the bending stiffness or stiffnesses of irregularly shaped panel elements capable of a bending wave acoustic effect, which enables the panel element to have a sufficiently distributed resonant mode character for this acoustic effect and allows the practically effective location or locations of the bending wave transducer device or devices to be determined (including finite element analysis), even independently of and without relating this to any imagined or intended shape known to be advantageous. Such procedures can be implemented pragmatically to some extent by trial and error, at least in terms of the spatial distribution of stiffness, but can also be facilitated by analysis of the same, for which, for example, finite element analysis can be used, at least in the sense of how low and high stiffness centers can be usefully created as shown here in order to achieve positive (approaching/attracting) and negative (repelling/repelling) placement effects on the effective location or locations of the transducer device within such spatial stiffness distribution, whether or not it is analyzable in itself.

In practice, useful advantages can be gained by seeking out structures and/or variations whereby a derivation or derivation can be made from what is known to be effective for a particular panel element geometry and structure, and which can and often will be effective for other panel geometries/structures, particularly to indicate the structural characteristics of such different panel geometries in terms of what is likely to be a successful areal stiffness distribution and where the transducer drive locations are.

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- 12 In one inventive approach, we have usefully focused attention on the transducer location or locations by imagining a half geometry, a desired or given panel element, and a reference geometry of a known effective panel element, for which a detailed analysis has been made or is available to ensure that the desired target transducer position coincides with the actual and preferred effective transducer position of the reference geometry. A bending stiffness map can then be created and thereby any or each selected structure relative to the now coincident transducer positions of the target and reference geometries and over such geometries the bending stiffness of the already analyzed reference panel structure can be changed relative to the target geometry in order to provide substantially the same or similar or proportionally the same stiffness distribution as the reference geometry and to produce an acoustically successful bending wave effect in the target geometry. Such promising structures include lines starting from coincident transducer positions and passing to or through the edges of the target and reference geometries (e.g., as if to illustrate bending wave transitions, crossings). The imagined relative modifications depend on the relative lengths of the same structural lines in the target and reference geometries and are dependent on a suitable relationship, which typically involves the ratio of bending stiffness (B) to mass per unit area (μ), or Β/μ, and proportional modifications involve the third and/or fourth powers of the lengths of the lines to the edges of the target and reference geometries. It is advantageous, or at least gives a more natural feel, if a target geometry is smaller than the corresponding reference geometry. Furthermore, for superposition, it is advantageous to strive for the smallest possible amount of excess of the latter over the former, including the smallest possible processing of the transformation. This can favor target and reference shapes of substantially similar types, or the favorable reference shape closest to the unfavorable target geometry.

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- 13 si geometry, however, we see it as advantageous if the targeted geometry differs significantly from any other identifiable type with a known favorable design/structure.

A good starting point for the reference geometry/structure is the panels described in the referenced international patent application, which have isometric surface bending stiffness and have been thoroughly studied/analyzed. In fact, another structural/modification approach could be considered suitable, in which a match is sought for the target geometry/structure in such a way that the (now common) transducer position divides the bending stiffnesses in the reference geometry/structure relative to itself. Furthermore, similar or related mapping methods could be used not only for different geometry types, but also in cases where one wants or requires a bending stiffness distribution for one type of target geometry that resembles or mimics another type of geometry in that a given type of usable geometry/design (e.g. rectangular or elliptical) does not have a decisive influence on the actual spatial distribution of resonant mode vibrations, which may be difficult to perturb to a large extent.

In the case of loudspeaker elements suitable for both piston and bending wave operation, the coincidence of the position of the bending wave transducer device with the center of mass and geometric center is particularly effective in that a single transducer device can be combined in a single location to realize both piston drive and bending wave excitation.

However, it is also possible to use separate transducers, one for piston-only operation, coinciding with the center of mass/geometric center, and another, located at a distance therefrom, preferably as described herein, for bending-wave-only operation, although in this case mass compensation may be required by using additional masses (if the required distribution of bending stiffness does not allow for this). According to the invention

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- A particularly interesting feature of solution 14 is the use of a single transducer that allows both piston operation and spaced-apart bending wave operation, but in spaced-apart positions, and such a single transducer can be used either to remotely achieve the position of the bending wave transducer as described herein (e.g. to accommodate a suitable transducer design), or to leave it as is, as would arise without the application of the above teachings of the invention.

In general, of course, the application of the solution according to the invention involves distributions of mass, namely in such a way that the center of mass is removed from the geometric center and/or from any transducer position or other. In fact, the bending stiffness and/or the change or changes of mass at least in the acoustically active region or regions of the panel element or elements are possible in a wide variety of ways and/or can be realized in a wide variety of distributions, usually gradually in any given direction for a desired purpose other than the present one, and the same generally exhibits an anisotropy that is asymmetrical at least with respect to the center of mass; and the use is made as in the case of the above international patent application.

Practical aspects of the invention include a loudspeaker drive unit comprising a frame, a transducer carried on the frame, a rigid and lightweight panel diaphragm in driving relationship with the transducer, and a flexible edge suspension surrounding the diaphragm, connecting the diaphragm to the frame, wherein the transducer is arranged to reciprocate the diaphragm to produce an audio signal at relatively low audio frequencies, and to cause the diaphragm to vibrate in a bending wave operation by bringing the diaphragm into resonance to produce an audio signal at higher audio frequencies, and the arrangement is arranged such that the transducer is connected to the center of mass and/or geometric center of the diaphragm, and the diaphragm has a variable distributed bending stiffness, which variation is arranged such that the diaphragm is acoustically effective (at least preferably at

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- 15 with the center of gravity shifted relative to the center of gravity).

The shape of the membrane may be circular or elliptical and the transducer may be connected to the geometric center of the membrane. The diaphragm may be a lightweight structure formed by a cellular core sandwiched between two opposing skin layers, and one of the skin layers may extend beyond the edge of the membrane and the edge of such extending skin layer may be connected to a flexible suspension.

The transducer may be of an electromagnetic system and may comprise a moving coil mounted on a coil-forming element, the coil-forming element being driveably connected to the membrane. A second flexible suspension may be connected between the coil-forming element and the frame. One end of the coil-forming element may be connected to the membrane and said second flexible suspension may be located adjacent said one end of the coil-forming element, and a third flexible suspension may be connected between the other end of the coil-forming element and the frame.

The end of the coil forming element near the panel membrane may be connected to substantially drive the panel membrane at a single point. A tapered device may be connected between the coil forming element and the panel membrane to accomplish this.

The coil-forming element may include a flexible section radially offset from a rigid section to reciprocate the diaphragm and provide off-center resonant drive for the diaphragm.

In other aspects, the solution according to the invention extends to a loudspeaker comprising the above-mentioned driving unit, and/or a diaphragm of a rigid lightweight panel loudspeaker driving unit, which is designed to be pistonically driven, and can be vibrated to resonance, and the center of mass of the diaphragm falls at the geometric center, and the center of rigidity thereof is shifted relative to the center of mass.

Brief description of the drawings

The invention will be described in more detail below with reference to the exemplary embodiments shown in the accompanying drawing. In the drawing:

Figures 1A-1D are a top view and three schematic cross-sectional views showing the hair on an acoustic panel element.

DANUBIA 90398-8071 - 16 the desired position of the vibrating wave transducer and implementing compression of a deformable core material or a shaped core or composite material;

Figures 2A, 2B, 2C outline a top plan view and cross-sectional views of the present elliptical acoustic panel element;

Figures 3, 3B, 3C are similar views of a different type of elliptical panel element;

Figures 4A, 4B and 4C show an unfavourable circular acoustic panel element which is converted into a more favourable one by means of a sub-elliptical groove/notch and show distribution diagrams with and without such groove/notch;

Figures 5A, 5B and 5C are diagrams useful for explaining possible maps/structures/modifications for the desired or targeted geometry of a rectangular panel element for deriving the stiffness distribution and for cross-sectional/profile representation of the results;

Figures 6A, 6B and 6C show relatively interesting diagrams compared to the useful method comprising Figure 5;

Figures 7A and 7B are side sectional and top views of one embodiment of a loudspeaker driver unit according to the invention, Figures 8A and 8B are side sectional views of another loudspeaker driver unit and a modified version thereof, Figures 9A and 9B are side sectional views of a further loudspeaker unit and a modified version thereof, Figures 10A and 10B are schematic views of a loudspeaker driver coupling or actuator for the application of a piston and bending wave effect in a spaced apart manner, and a detail of the mounting to the diaphragm/panel element; and Figures 11A and 11B illustrate the relationships of such effects and the sound change.

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- 17 Best Mode for Carrying Out the Invention

Figure 1A shows a substantially rectangular acoustically distributed mode panel element 10A, as if it were formed directly as a result of the above-referenced international and UK patent applications and thus their "natural" location 13 for the bending wave transducer element is spaced apart from the geometric center 12 and is located outside the actual and dashed line diagonal 11. However, according to the application of the solution according to the invention, the location of the transducer 13 should be at the geometric center 12 of the panel element 10A, i.e. it actually appears as if it is shifted along the continuous line 15, which is achieved by distributing the bending stiffness of the panel element 10A appropriately in space. To this end, the bending stiffness is made relatively larger on one side (right in Figure 1A) and smaller on the other side (left in Figure 1C) of the geometric center 12 relative to the center and the natural transducer location 13, namely along the line 15 and its straight line extensions 15G and 15L in opposite directions.

Figure 1B is a schematic section taken along line 15 including extensions 15G and 15L, and shows the same position as Figure 1A, i.e. the natural transducer position 13B, which is also spaced from the geometric center 12B of the distributed mode panel element 10B, as shown by projection lines 12P and 13P. Figure 1B does not show the details of the actual structure of the panel element 10B; but indicates the possibilities in that it indicates the continuous outer surfaces 16X, 16Y with a solid line, or indicates the sandwich type structure shown by the inner surfaces 17X and 17Y with a dashed line, which indicates the plane where the cover layers are connected to an inner core 18, which is typically (but not necessarily) of a cellular foamed type or a continuous cellular honeycomb structure.

Figure 1C illustrates the use of an 18C core made of a material that is deformable, namely compressible, to the extent that it is suitable for being collapsed to a reduced thickness, as is typical of many foamed cellular materials suitable for making distributed mode acoustic panel elements.

DANUBIA 90398-8071 and from which we started in the case of Figure IC. Such a collapse is shown by the thickness of the core 18C, which decreases from right to left in Figure IC and its cells change from a round open shape 19X to a flattened shape 19Y. Of course, it is not important for these cells to be of the same or similar size or to be arranged in a regular arrangement or to be round completely open at the greatest thickness (suitable foamed materials are often detailed embossed foamed types). The core 18C is further shown with facing cover layers 17A, 17B. It is conceivable or even normal to deform the core material 18C to the desired profile before the cover layers 17A, 17B are attached, but this is not necessary as the element 10C is still suitable for distributed mode acoustic operation if it is deformed by pressure after the cover layers 17A, 17B are attached. The resulting greater and lesser thicknesses of the core 18C and the panel element 10C have correspondingly greater and lesser bending stiffnesses and in the case of a profile of gradually varying thickness and thus varying stiffness the change is such as to bring the position of the transducer 13C into a position coincident with the geometric centre 12C, as shown by the arrow 13S and the reference marks 13C circled together with it. The ring or dent deformation can generally be facilitated by heat treatment or heat effect and by means of a pressure plate of suitable profile. The center of mass of the panel element 10C does not change, i.e. its center of mass continues to coincide with the geometric center 12C, which now also coincides with the transducer position 13C.

Where the contribution of the core density is small, i.e. the bending stiffness is dominant, then the linear factor characterizing the contribution of the core mass can be neglected and the desired areal thickness distribution can be achieved by shaping the thickness of an isotropic core, or a polymeric foam, or a manufactured honeycomb sandwich, or a monolithic structure without a face layer and core; and any such structure can be fabricated, machined or cast in accordance with the requirements herein.

Figure 1D shows a distributed mode acoustic 10D panel element with a gradually lightened bottom surface,

DANUBIA 90398-8071 - 19 _ and thereby its thickness is reduced in a manner similar to that of FIG. 1C. Such a profile may vary somewhat from the previous one in order to achieve the same effect, i.e., the coincidence of the transducer position 13D with the geometric center 12D, which depends, for example, on the material or materials used for the panel element 10D. Such materials may be monolithic reinforced composite materials or any type of cellular materials, typically in this case formed with a core provided with a cover layer, including a honeycomb panel in which the cells are formed in a continuous manner from one cover layer to the other. The structure 19Z shown in FIG. 1D and similar to the foamed cell may be the same by using a foamed material which is not incidentally dented or not suitable for denting; and it is not intended to indicate otherwise that its density does not change significantly. This will naturally cause the mass distribution to vary and the centre of mass of the panel element 10D to be displaced away from the geometric centre 12D, generally in the direction of the arrow CM. In order to ensure that the resultant centre of mass coincides with the geometric centre 12D, the panel element 10D is provided with at least one additional balancing mass 22 as shown, which is preferably mounted in a blind hole 23, and preferably by means of a semi-flexible or elastic means 24, for example in a suitably mechanically or adhesively secured sleeve or bushing, whereby the inertial pressure is gradually decoupled or separated from the panel element 10D at higher frequencies to achieve the desired vibration distribution. More than one balancing mass 22 may be used, for example at a position less than 180° along the imaginary line 15L extended, or in some other arrangement, they need not all have the same mass, for example their mass gradually decreases as they move away from the line 15L.

The simplest is to simply taper the thickness along the section of Figure 1B, although a more complex tapering method is also normal, including a solution in which the thickness at the edges is common and uniform and/or gradually decreases away from lines 15, 15G, 15L. The relationship between bending frequency and size is

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- 20 should be taken into account using metric relations. For any given shape, increasing its size reduces the fundamental harmonics of vibration and vice versa. The effective displacement of the selected transducer position can be considered equivalent to shortening the effective panel size in relation to the bending along the direction of such displacement.

Figures 2A-2C and 3A-3C show substantially elliptically shaped panel elements, of which panel elements 20A, 30A are isotropic in nature, and thus their geometric center 25 and their center of mass 35 coincide. To a significant extent, in the context of isometric panel geometry and structure, the stiffness distribution is naturally also centered around the geometric centers 25 and 35, whether a high center (rigidity itself) or a low center (softness or flexibility). Figures 2A and 3A also illustrate the superior or best position (as in the above-referenced international patent application) for a bending wave transducer, which is operationally desirable for resonant mode acoustic operation of panel elements 20A, 30A, for example as or in a loudspeaker.

In the case of Figures 2B, 2C and 3B, 3C, the marked centers 25, 26, 35 and 36 of the panels 10B, 20B, 30B are still identical to both the geometric center and the center of mass (25, 35), but are now additionally identical to the acoustically effective bending wave transducer position 26, 36. Compared to Figures 2A, 3A, the transducer positions 26, 36 are effectively shifted due to the distribution of bending stiffness or stiffnesses here, and this is accompanied by a displacement of the centers of high and low stiffness 27, 28 and 37, 38, which are generally opposite to the geometric centers 25, 35. This different asymmetric stiffness distribution in the illustrated case is the result of the gradual change of the cells 29, 39, practically a change in their height, which is accompanied by a change in the thickness of the panel elements 20A, 30A, but also changes the area and location density of the cells (Figures 2B, 2C), or their area and wall thickness, but not their location density (see Figure 3B, 3C), by which the desired distribution of stiffness is achieved in terms of mass.

DANUBIA 90398-8071

- 21 without any significant disturbance of its distribution, at least from an operational point of view, and thus its center of mass now coincides with both the geometric centers 25 and 35, and with the transducer positions 35 and 36, respectively.

The change in stiffness or stiffnesses and thus their spatial distribution can also be envisaged by other methods, for example by non-planar shapes, such as hairpins, curvatures, etc., which generally influence the stiffness in a well-understood way, or it can be implemented by grooves, slots or incisions, which can be formed in the surface to reduce the stiffness, but it is possible to increase the stiffness with ribs, which includes a gradual change by arranging such elements in a series spaced apart from each other, which can take place, for example, along the extensions of lines 15G, 15L in Figure 1A (this is not shown, but can be calculated using finite element analysis).

Figure 4A shows how a recessed groove, slot or notch can be used to improve the distributed mode bending wave performance of an acoustic panel element 40, which in this case has a shape or geometry, namely circular, which is known to be disadvantageous as a distributed mode acoustic panel element, especially when the excitation transducer device is centrally located. This known inadequacy of functionality is reflected in the modal frequency distribution shown in Figure 4B, which disadvantage will be readily recognized and understood by those skilled in the art, as it corresponds to a concentric vibration distribution. A significant improvement can be achieved, as shown in Figure 4C, by a partially elliptical groove 45, otherwise known as a slot or notch, and thus falls into the class of designs/geometries that include some of the very favorable distributed mode acoustic panel elements (as in the case of Figures 2 and 3 previously described), although it does not actually correspond to such a known favorable characteristic ellipse. However, the effect on the low frequency modal operation is significantly more distributed than the symmetry of simple centrally excited circular shapes and the higher frequency modal effect can reach and extend beyond the open ends of the groove 45. The shape of the groove 45 is determined by finite element analysis methods.

DANUBIA 90398-8071

- 22 was designed using the elements and a complex element arrangement was selected, and such a method is of general value for the detailed implementation of the present teaching. Less curved shapes placed asymmetrically with respect to the center of the circular panel element also proved promising, which should be further refined by further application of the finite element analysis method.

Figures 5A and 5B show structures and modifications most in line with the above, particularly the rectangular target geometry 51A and 51B and the reference geometry/shape 52A, 52B. The construction lines 53A, 53B, developed according to the different lengths and desired/required bending stiffnesses, show very promising efficiency in the case of this solution, at least with respect to the same rectangular type shapes. The method shown in Figure 5B is particularly attractive in that the reference design/geometry 52B can be efficiently constructed from the target design/geometry 51B, which is placed at one corner by extensions from one corner, whereby the location of the transducer 54B, which is a well-known and analyzed isometric shape 52B, simply coincides with the geometric center of the target shape 51B. Figure 5C shows a typical cross-section of the target element 50 for the target shape 51A, which is obtained as a result of the method illustrated in Figure 5B.

Based on the study of the Β/μ ratio or B and/or μ parameter values - especially alone, while keeping the other constant - in the different 53B radial directions and from the mathematical mapping of the panel shape 52B to the shape 51B, it is possible to calculate its stiffness distribution along the 53B directions, using a power relationship that includes the fourth power of the length and the second or third power of the thickness, depending on whether the bending stiffness of a sandwich panel formed from a core with a cover layer or a monolithic solid composite structure without a cover layer is required.

Figure 6A shows the ratiometric results of the length mapping method of Figure 5B, and Figure 6B shows how the required (target) bending moment relates to the

DANUBIA 90398-8071 behavior to the ratiometric results according to Figure 6A, and to the material properties, in particular the stiffness alone containing the fourth power of the length (solid line), the sandwich structure containing the second power (dotted line) and the thickness of the monolithic structure containing the 4/3 power (dashed line). For a sandwich structure, the stiffness of the cover layer (tensile strength) also contains the fourth power of the length, and the thickness of the cover layer contains the four-thirds power. Figure 6C shows a modal density map with 3% damping for a rectangular target panel element without a flexural stiffness distribution, and a reference isometric panel element with an aspect ratio of 1.134.1 according to the above international patent application, i.e., adjusted for the difference of only one side, and a rectangular panel enhanced with a flexural stiffness distribution according to the parameters of the cover layer, namely the thickness (h) and Young's modulus (E).

Figures 7A and 7B show a loudspeaker drive unit having an open frame-shaped frame 71 in the form of a relatively flat basket or bowl and having an outwardly extending peripheral edge 71F and holes formed therein, whereby the loudspeaker drive unit can be mounted on a plate (not shown), for example in a sound cabinet 1 (not shown), in a generally conventional manner. The frame 71 carries a transducer 72 in the form of an electrodynamic drive motor, the magnet 73 of which is located between pole pieces 74A and 74B, which form an annular air gap in which a tubular coil-forming body 75 is placed, on which a coil 75C is located, and which forms the drive coupling or actuator movable element of the motor.

The coil forming element 75 is mounted on flexible suspensions 76A and 76B at two opposite ends, which guide the coil forming element 75 for axial movement in the air gap of the magnet unit. One end of the coil forming element 75 is attached, for example by adhesive 77, to the rear surface of a lightweight rigid panel 70, which panel 70 forms an acoustic radiating membrane in the loudspeaker driver unit and which has a lightweight cellular core 70C, for example honeycomb.

DANUBIA 90398-8071

- 24 of structural material and sandwiched between two opposing front and rear cover layers 70F and 70R. The panel 70 is substantially designed in accordance with the present invention, namely with a distribution of bending stiffness, which allows its center of mass and the location of the designated bending wave excitation to be at the geometric center. In the example shown, the front cover layer is preferably conventionally designed in a circular shape, which merges with the contour and in some cases is in accordance with the environment/suspension during actual operation. The rear cover layer is chosen to be rectangular, thus forming a composite panel in accordance with the distributed mode teaching (driven directly by the differential coupler according to FIGS. 10A and 10B).

For a simple centered or centered-equivalent drive, the distributed mode panel section according to the present invention should be designed with a preferred or preferred modal distribution, which can be achieved, for example, by controlling the areal stiffness, in order to advantageously locate the modal drive point or area at or near the geometric and mass center. This allows good modal drive at higher frequencies and piston operation at lower frequencies with the design and geometry of the drive in a conventional style.

The cover layer 70F on the front side of the panel 70 extends beyond the edge of the panel and its peripheral boundary is connected to the roller environment or suspension 77 carried by the frame 71, whereby the panel is free to move in a piston-like manner. The transducer 72 is designed to move the panel 70 piston-like at low frequencies and to vibrate the panel 70 at high frequencies, thereby generating bending waves therein, causing it to vibrate longitudinally as previously described.

The arrangements of Figures 8A and 8B are substantially similar to those described above, except that in this case the frame 81 is even shallower or flatter, and the motor 72 is largely located outside the frame 81, and the coupling/actuator coil-forming element 85 extends into the frame 81, which

DANUBIA 90398-8071

- 25, the suspension of 86 must be modified. The version according to Figure 9B allows for a smaller Y-shaped neodymium motor 82N and a narrowing of the final section 85A of the coil-forming element 85.

The arrangements of Figures 9A and 9B are largely similar to the arrangement of Figures 8A and 8B, except that the coil-forming element 95 is formed with an elongated end 95A, 95B (single) or double conical shape, the apex 95P of which is connected to the rear surface of the lightweight rigid panel at the geometric center thereof.

10A, 10B illustrate a diaphragm coupler/actuator 100, which is conveniently a coil-forming element of a drive motor (not shown), having a main curved peripheral portion 108 at its drive end adapted to be connected to a rigid, lightweight panel 100 of semi-flexible material by means of a reinforcement 107, while a curved peripheral portion 109 at the same end is rigid. At low frequencies, the drive applied to the panel 100 is of a piston nature, which is transmitted by both curved peripheral end portions 108 and 109. At high frequencies, the coupler/actuator 100 generates a bending wave effect by means of a smaller portion 109 and transmits the vibration energy to the panel 100 in a position offset from the axis of the coupler/actuator 105. Due to its semi-flexible nature, the larger curved peripheral end portion 108 remains essentially at rest. Thus, the actual actuation point or position of the drive is frequency dependent, even though the same device 105 is acting in the same manner.

The simpler illustrated case of one direct coupling section and one semi-flexible section can be extended to multiple rigid connection points and more complex semi-flexible arrangements, for example, where two or more distinct distributed mode panel element transducer positions may be involved. The semi-flexible section may be tapered or stepped, or may be formed with a multi-step thickness or joint property, in order to provide a graded coupled stiffness, which can be interactively calculated with the acoustic property specifications of the panel to improve the joint quality, even if a distributed mode acoustic panel is used in which the 100 couplers

DANUBIA 90398-8071

- 26 has a transducer position that is spaced from the geometric/center of mass, matching the appropriate structure formed for the actuator, or the latter is matched to, for example, the transducer positions described in the above international and UK patent applications.

Such a differential frequency coupler 105 can be used in conjunction with a conventional motor coil used in electrodynamic exciters. Such a coupler 105 can be a separate component of predetermined size or diameter, but it is also advantageous to use it as part of the coupling plane of a motor coil of similar diameter, which diameter can be selected as described above to cover one or more preferred driving transducer positions on a distributed mode acoustic panel element, namely those located at the rigid end portions 108 and from which they receive drive at higher frequencies to achieve the intended frequency response, which is achieved by the distributed mode bending mode vibration of the acoustic panel membrane element 100. At lower frequencies, the semi-flexible parts/inserts 108 play a greater role and gradually make the entire contour of the coupler/actuator 105 effective to achieve a balanced center of mass effect and thereby achieve a satisfactory piston effect at low frequencies. The fundamental bending frequency of the panel element 100 and the elasticity of the coupler/actuator part or layer 108 are chosen so that the acoustic performance smoothly transitions from the piston action to the bending vibration ranges as a function of frequency. This transition can be further facilitated by the part or parts 108 being formed with multiple steps or tapers 108.

The operation of this coupler 108 can be better understood from Figure 11A, which illustrates the intended change in velocity transmitted to the acoustic panel, and which diagram includes the range of the sound transition. At low frequencies, the semi-flexible portion or portions 108 communicate or communicate effective energy to the panel element 100 in a balanced piston-like manner. This piston-like effect decreases with increasing frequency as the mechanical impedance of the vibrating panel element 100 becomes increasingly dominant and ecDANUBIA 90398-8071

- It receives excitation at the eccentric location or locations designated at 27. Thus, at higher frequencies, the active transmission of speed from the rigid, displaced sector or sectors of the coupler becomes increasingly significant.

Figure 11B further illustrates the frequency dependent displacement of the piston drive and the distributed mode excitation points. At low frequencies the piston drive point is predominantly in the center and at the center of mass. As the frequency increases the drive is increasingly shifted to an excitation point located further from the center, which excitation point is determined by the appropriate choice of panel shape and the diameter of the composite coupler/actuator and its arrangement at or near the designated distributed mode point, and thus a satisfactory and favorable distribution can be obtained in the vibrating mode.

In the case of the above 7A, 7B, such bending wave transducer devices have an overall diameter of between 150 and 200 mm and provide satisfactory bending wave performance in the range of 150Hz-500Hz, operating at the natural transducer location or locations of a distributed mode panel element. The piston operation becomes effective at lower frequencies, for example from 30 Hz in the case of appropriate acoustic mounting, and gradually decreases in its upper range as the panel element enters the bending mode region.

The differential frequency-dependent properties of the couplers of the invention allow for complex refinements in the use of distributed mode acoustic panel elements. For a given panel, for example, a frequency-dependent variation of the folding point may be desirable for frequency control in certain applications, such as when a small enclosure is used with a close-to-wall assembly and the associated response-modifying environment. More than one semi-flexible element or insert of a suitable shape and/or size/area may be used in order to gradually or stepwise and effectively shift the folding point that is most effective from the frequency-dependent modal arrangement and advantageously modify the radiated sound.

Claims (45)

DANUBIA 90398-8071 - 28 PATENT CLAIMS 1. An acoustic device comprising an element having a transverse extension relative to its thickness and capable of sustaining bending waves causing an acoustic effect in the operating acoustic frequency range by means of the spatial distribution of the resonant mode of natural bending wave vibrations on its surface, where the bending stiffness of the element varies along its surface, which makes the element more favorable for the spatial distribution of the resonant modes for the acoustic effect, and the center of the bending stiffness of the element is in a position shifted from the geometric center of the element. 2. Acoustic device according to claim 1, characterized in that the center of mass of the element is located at the geometric center. 3. An acoustic device according to claim 2, characterized in that the variation of the bending stiffness at different sides of said location of the bending wave converting device shows relatively higher and relatively lower bending stiffness. 4. An acoustic device according to any one of claims 1-3, characterized in that the variation in bending stiffness comprises relatively greater and lesser bending stiffness on different corresponding sides of the geometric center of the element or area. 5. An acoustic device according to claim 3 or 4, characterized in that the high center of bending stiffness, where the first moment of stiffness is zero, is on one side of the geometric center of the element, and the low center of bending stiffness, where the first moment of the reciprocal of stiffness is on the other side of the geometric center of the element. 6. An acoustic device according to any one of claims 1-5, characterized in that the element is provided with an additional mass or masses which are selectively arranged in a manner that substantially has no effect on the desired acoustic effect. 7. Acoustic device according to any one of claims 1-6, characterized in that the element has an additional mass DANUBE 90398-8071 - 29 or masses which are selectively arranged in a manner that substantially does not affect the desired acoustic effect. 8. An acoustic device according to claim 7, characterized in that the or each additional mass is of a sufficiently small mass so as not to substantially affect the lower frequency acoustic effect and the element is associated with a means that substantially effectively decouples the or each additional mass from the higher frequency acoustic effect. 9. An acoustic device according to claim 7 or 8, characterized in that the additional mass(es) are positioned such that the center of mass of the element and the additional mass is at the desired location of the element. 10. Acoustic device according to claim 9, characterized in that the desired location coincides with the geometric center of the element. 11. An acoustic device according to claim 6, characterized in that the element has a sandwich structure formed by cover layers located on a core, the core having walls defining cells extending through the variable thickness between the cover layers, the cells being formed with different cross-sectional dimensions in order to create the required mass distribution of the element. 12. An acoustic device according to claim 6, characterized in that the element has a sandwich structure formed by covering layers on a core, which core has walls defining cells and passing through the covering layers of varying thickness, wherein the walls defining the cells have different thicknesses in order to achieve the required mass distribution of the element. 13. An acoustic device according to claim 11 or 12, characterized in that the prescribed distribution of mass is centered around the geometric center of the element or area. 14. The acoustic device of claim 1, characterized in that it comprises at least one local modification of the element in the variation of the bending stiffness, which modification is at least one relative weakening groove, slot or notch formed in the element. DANUBIA 90398-8071 15. An acoustic device according to claim 14, characterized in that the local variations in the distribution of bending stiffness partially define an undefined subgeometry on the element, and the arrangement is favorable for the bending wave acoustic effect by effectively modifying the surface distribution of the lower frequency modes of vibration dependent on bending waves in a desired manner relative to said location of the bending wave transducer. 16. An acoustic device according to claim 15, characterized in that the local variations in the distribution of bending stiffness allow, in addition to said local variations, higher frequency modes of vibrations dependent on bending waves. 17. Acoustic device according to any one of claims 1-5, characterized in that the structure of the element includes a cover layer and the change in bending stiffness is achieved by changing the parameter(s) of the cover layer. 18. The acoustic device of claim 17, wherein said parameter of the cover layer is the thickness of the cover layer. 19. An acoustic device according to claim 17 or 18, characterized in that the parameter of the cover layer is the Young's modulus of the cover layer. 20. An acoustic device according to any one of claims 1-19, characterized in that one or said locations of the acoustically effecting bending wave transducer device are used for the piston-effect acoustic transducer device. 21. An acoustic device according to claim 20, characterized in that it comprises an acoustic transducer device arranged at said location, having both a bending wave and a piston effect. 22. A loudspeaker drive unit comprising a frame, a transducer carried by the frame, a rigid, lightweight panel diaphragm forming an acoustic device according to any one of the preceding claims, connected to the transducer by a driving connection, a flexible side suspension surrounding the diaphragm and connecting it to the frame, wherein the transducer produces an audio frequency output signal at relatively low audio frequencies. DANUBIA 90398-8071 - 31 is arranged in a manner that causes the diaphragm to produce an audio frequency output signal by resonating the diaphragm by driving the diaphragm pistonically and causing it to vibrate at relatively higher audio frequencies, and the transducer is operatively connected to the center of mass and/or geometric center of the diaphragm. 23. A loudspeaker driver unit according to claim 22, characterized in that the diaphragm is circular or elliptical in shape. 24. A loudspeaker driver unit according to claim 22 or 23, characterized in that the membrane comprises a lightweight cellular core sandwiched between two opposing cover layers. 25. A loudspeaker drive unit according to claim 24, characterized in that one of the cover layers extends beyond the edge of the membrane and the boundary portion of the extending cover layer is connected to the elastic suspension. 26. The loudspeaker driver unit according to any one of claims 22-25, characterized in that the diaphragm is a distributed mode resonant panel. 27. A loudspeaker drive unit according to any one of claims 22-26, characterized in that the transducer comprises an electromagnetic system and a moving coil mounted on a coil-forming element, and the coil-forming element is operatively connected to the diaphragm. 28. A loudspeaker drive unit according to claim 27, characterized in that it comprises a second flexible suspension connected between the coil forming element and the frame. 29. A loudspeaker drive unit according to claim 28, characterized in that one end of the coil forming element is connected to the membrane and the second elastic suspension is located next to the first end of the coil forming element, and a third elastic suspension is connected between the other end of the coil forming element and the frame. 30. A loudspeaker drive unit according to any one of claims 27-29, characterized in that the end of the coil forming element adjacent to the diaphragm panel is connected to the diaphragm in a manner that drives the diaphragm panel substantially at a single point. 31. The loudspeaker driver unit according to claim 30, characterized in that the coil forming element and the diaphragm pa DANUBIA 90398-8071 - A conical device is connected between 32 of its teeth. 32. A loudspeaker comprising a driver unit according to any one of claims 22-31. 33. A rigid, lightweight panel loudspeaker driver unit diaphragm configured to be piston-driven and resonantly vibrated by bending waves, the diaphragm having a center of mass located at its geometric center and a center of stiffness distribution offset from the center of mass. 34. An acoustic device according to any one of claims 1-21, characterized in that the element has a bending wave transducer means for generating said acoustic effect, which is located in a position determined by the spatial distribution of bending stiffness. 35. Actuator unit for a loudspeaker drive unit having flexible and rigid drive coupling parts for driving a diaphragm centered on an axis by pistons and for realizing non-centered resonant excitation in the diaphragm. 36. The actuator of claim 35, wherein the flexible portion is configured to drive the diaphragm in a piston-like manner at low frequencies, and the off-center resonant excitation is transmitted to the diaphragm by at least one rigid member at higher frequencies. 37. An acoustic drive unit comprising a loudspeaker drive unit actuator according to claim 35 or 36, which, when coupled to the diaphragm, induces a distributed mode acoustic effect in the diaphragm, at least at one high frequency, via at least one rigid member. 38. An actuator unit according to claim 35, 36 or 37, characterized in that the rigid component(s) also contribute to the piston drive. 39. An actuator according to any one of claims 35-38, characterized in that the components form the contour of the end of the tubular element. 40. A loudspeaker drive unit comprising an actuator according to claim 39, characterized in that the tubular member is attached to the diaphragm. 41. A method according to any one of claims 1-21. DANUBIA 90398-8071 - 33 for making an acoustic device panel element, during which process the nominal position of the bending wave transducer device is determined without a change in bending stiffness and the spatial distribution of the bending stiffness of the element is controlled, including the implementation of bending stiffness changes that move said nominal position of the bending wave transducer device to a desired position, during which relatively greater and lesser bending stiffness is formed on opposite sides of the desired actual position and on opposite sides of the nominal position. 42. The method of claim 41, characterized in that the relatively greater and lesser bending stiffness is formed along the extent of a nominal straight line passing through the desired and nominal positions. 43. A method for producing a panel element according to claim 41 or 42, comprising superimposing in imagination a desired or given design panel element shape as a target geometry and a reference geometry of a panel element known to be effective, with available detailed analysis, in such a way that the desired edge transducer position coincides with the actually and outstandingly effective transducer location of the reference geometry. 44. The method of claim 43, wherein the known arrangement or geometry is an extended arrangement starting from one or more edges of the actual unfavorable arrangement or geometry. 45. The method according to claim 43 or 44, characterized in that during the conversions, the fourth power of the length and other powers are used for the bending stiffness as such, which are related to the determination of other parameters, for example the monolithic structural thickness of the element or the sandwich structure of the element or the cover layer or layers of the sandwich structure, or the Young's modulus. The representative: