MXPA00007086A - Active acoustic devices comprising panel members - Google Patents

Abstract

Active acoustic device comprises a panel member (11) having distribution of resonant modes of bending wave action determining acoustic performance in conjunction with transducer means (31-34). The transducer means (31-34) is coupled to the panel member (11) at a marginal position. The arrangement is such as to result in acoustically acceptable action dependent on said distribution of active said resonant modes. Methods of selecting the transducer location, or improvement by location of localised marginal clamping, rely on assessing best or better operative interaction of said transducer means (31-34) and the panel members (11) according to parameters of acoustic output for the device as an acoustic radiator.

Description

ACOUSTIC DEVICE AND METHOD TO MANUFACTURE IT FIELD OF THE INVENTION This invention relates to active acoustic devices and more particularly to panel elements in which the action or acoustic performance depends on the beneficial distribution of the resonant modes of the action of the bending waves in such panel elements. and of the related surface vibrations, and to methods for producing or improving such acoustic devices. The term "distributed mode" for such acoustic devices, including radiators or acoustic loudspeakers, should be used in the present application and it should be understood that the term "panel-form" implies such modality action distributed in a panel element unless the context so requires. prevent. In panel-shaped loudspeakers or the like, these panel elements function as distributed-mode acoustic radiators that depend on the action of bending waves induced by input means that apply a mechanical action to the panel element, and of excitation Resulting from the resonant modes of the action of the bending waves cause surface vibration for the acoustic output by coupling with the ambient fluid, usually the air. There is revealing infoxmation on such acoustic radiators (within a wider class of distributed and active acoustic and passive acoustic devices) in our international patent application WO97 / 09842 and several of our subsequent patent applications deal with aggregates and useful developments thereof.

BACKGROUND OF THE INVENTION Until now, the locations of the transducers have been considered viable and of optimum efficiency when they were incorporated into the panel element displaced largely from their center, at least for the panels that are substantially isotropic with respect to the resistance to flexion and exhibiting a substantial constant axial anisotropy with respect to the flexural strength (s). The aforementioned WO97 / 09842 patent application provides specific guidance in terms of optimal proportional coordinates for the location of such built-in transducers, including alternative locations and indicates the preferential combinations of certain coordinates when two or more transducers are employed. Several advantageous applications of acoustic form-panel devices have been announced, including the incorporation of non-intrusive surface sheets or layers. For example, a physical combination in a coating that can be virtually indistinguishable is feasible. It is also possible a functional combination with other purposes, such as visual representation, including images, posters, writing and erasing boards, projection screens, etc. The ability to effectively hide visible transducers is enough for many applications. However, there are potential practical applications in which it would be useful to leave more extensive regions of the panel, especially the central ones, without any obstruction, not even of transducers hidden from view. For example, in the case of video devices or other applications where it is necessary to see through, it is not worth trying to obtain translucency or transparency of the elements of the panel with such built-in transducers, although an acoustic form-panel would be very attractive if it presented medium surfaces that did not obstruct visibility.

SUMMARY OF THE INVENTION According to one aspect of the present invention, there is provided a shape-panel acoustic device comprising an acoustic panel element of distributed mode with transducer elements located in a marginal position, arranged in such a way as to obtain an effective distribution and an excitation of the vibration in the resonant, acoustically acceptable mode. The existence of such convenient marginal positions as location of the transducer elements is established in the present application., as well as valuable information about the reasonable selection or improvements that can be introduced to such locations. Such a reasonable selection could be made through the investigation of an acoustic or loudspeaker radiator device that studies the convenient introduction of vibratory energy into the panel element, for example through an adequate evaluation of the acoustic output parameters of the panel in question when it is excited in marginal positions or locations. At least, the optimal results also apply to microphones. At the date of the present invention, the pertinent information in the background indicates that the existence of such marginal locations successfully is, to put it mildly, unlikely. In fact, the more related prior art cited in the application O97 / 09842, namely the application WO92 / 02024, constituted the starting point for the further developments particularly in terms of turning the excitation into its angles. Such developments implied the conclusion that the action of the bending wave in the distributed resonant mode as required for a viable acoustic performance results in a high vibrational activity in the panel angles, as well as a factor in the edges of the panel , as usual. The intuitive idea at least, confirmed to a large extent by the practical success obtained by locating transducers outside the center but well incorporated, is that the high vibratory activity is strongly combined with the margins of the panels, evidently allowing limited access and probably an effect on the material of the panel element as a whole and that this multiple combination contributes to the non-viability previously noticed of edge excitation. In the particular application of the present invention, an acoustic panel element, or a region thereof that is transparent or translucent may be convenient. The usual shape of the panel elements is polygonal, and often substantially rectangular. The multiple transducer elements may be at or near different edges, at least for the substantially rectangular panel elements. The transducer, or each of the transducers in question, can be piezoelectric, electrostatic or electromechanical. The transducer, or each of the transducers in question, may be arranged so as to refract compression waves towards the edge of the panel and / or to cause a lateral deflection of the edge of the panel to refract transverse bending waves along the edge. of a panel, and / or to apply a twist through a panel angle, and / or to produce linear deflection of a local region of the panel. The evaluation of the acoustic output of the panel elements can be relative to convenient acoustic output criteria, among which the power output intensity and consequently the conversion efficiency of the mechanical input vibration (and automatically also the customary electric excitation factor) in acoustic output, the uniformity of the power output as a measure of the regularity of the excitation of the resonant mode of the action of the bending wave, the inspection of the power output in terms of frequencies of excited resonant modalities, including the number and distribution or ranges of such frequencies, which are all indicators of utility. Such evaluations of the viability of the locations of the transducer elements constitute, individually or together, aspects relating to the methods described in the present invention. As an aid for evaluating at least the uniformity of the power output, it is also proposed here to use techniques based on the mean quadratic deviation with respect to a reference value. The use of the inverse of the mean square deviation offers the advantage of allowing to evaluate the uniformity according to values and / or positive representations directly. A convenient reference value can be individual with respect to each case considered, for example based on the median, as represented graphically by means of a uniform line that covers the actual measured power output over a frequency range of interest. It is significantly useful for the purposes of the evaluation of the mean square deviation with respect to the reference value, the adoption of a standardized standard format and that the measured acoustic power output conforms to that standard format. The standard format can be a straight line in a graph, preferably a flat straight line corresponding accordingly to a given constant reference value, and more preferably the same line or value as naturally applied to a distributed mode panel element at higher frequencies, in which modalities and modal action are more dense or densest possible. In this regard, it is evident and worth noting that, whatever the function necessary for such normalization to a substantially constant reference, it also constitutes an effective basis for an equalization function applicable to the input signals in order to improve the lower frequency acoustic output. It so happens that the distributed mode panel elements feasible as such, and preferably in the dimensional proportions and bending strengths as described in our previous patent application, can naturally have acoustic power output characteristics relative to the frequency that they decay progressively towards the lower frequencies and along them, where the resonant modalities and the modal action are less dense, however, since their frequency distribution as such is usually advantageous for the acoustic action in such a lower frequency range, Similar equalization of the input signal can be useful. This lower acoustic power output at low frequencies is related to the free vibration of the edge of the panel elements as such, and with the consequent greater loss of power at low frequencies, whose higher proportion tends to radiate and / or dissipate poorly, even to short-circuit completely in the vicinity of the free adjacent panel edges. As expected, such effects of power loss at low frequencies are significantly greater in the panel elements with transducers located on or near the edges and / or lower stiffness, compared to panel elements having transducers incorporated in the board. However, apart from any equalization of the input signal, these effects can be significantly mitigated by mounting baffles around the panel elements and / or fixing the edges of the panel elements. In fact, the spaced edge fasteners can have a selective beneficial effect with respect to the frequencies with wavelengths greater than the spacing between the fasteners. It is interesting to note that, in the case of panel elements of rather high stiffness, the viable marginal positions of the transducers comprise locations that have a correlation in the direction of the edge with the incorporated locations in the case of preferred transducer means in the applications, in prior art or in practice, such as those specifically cited in our previous patent application. When using transducer means in pairs, a preferred embodiment presents marginal locations of transducers with said correlation corresponding to the largest area that conceptually encompasses. In the case of a substantially rectangular panel element, said correlation can be done by means of cartesian or orthogonal coordinates, with said first preferred embodiment represented by the association of the transducer means with opposite quadrants in the diagonal direction. However, this referred to a particularly high stiffness / Q panel element, and it is not always true, even in the case of quite rigid panels (although not so much). See below for a promising operation associated with some adjacent quadrants or quadrants. In the case of an elliptical-shaped panel element, said correlation / correspondence can be made according to lines relating to the hyperbolic resonant mode, towards the edge and through the incorporated locations. Various other pairs of viable and feasible edge locations, although less convenient for the transducers, were found in investigations on orthogonal vectors that rotate around preferential incorporated locations of the transducers, including positions located on or near the angles of the panel elements. Another aspect of the invention relating to excitation at or near the angles refers to the convenient mass or clamping load substantially realized on the optimized or preferential built-in exciter speaker, where it appears that such an optimal driver (s) with mass loading behaves (effectively) to some extent useful as a "virtual (s)" source (s) of bending wave vibrations in the element. The latter may not prevent the central intrusion of the mass charge but is clearly related to a satisfactory marginal excitation at the angles. Further investigations have been carried out that include panel elements with different stiffness, especially some with fairly high stiffness, but also others with intermediate stiffness and much less. In each case it was the usual essentially rectangular configuration with dimensional proportions and axial flexural strength similar to those described in WO97 / 09842. In the case of the stiffer element, the evaluation based on the uniformity of the power output for the locations of individual transducers along the longer and shorter edges generally confirmed the preferential positions of the coordinates above. indicated, ie peaks for the best locations of individual transducer elements, as expected. On the other hand, however, the longer edges offered advantageous intervals of the measure of uniformity within 15% of the peak at transducer locations between the positions of the coordinates of each half of the edge and beyond these positions, up to about one third of the length from each angle; and within approximately 30% along at least one quarter of the length positions. In the case of the shorter edges, the intervals of the measure of uniformity were within 10% between the positions of Tas coordinates and within 25% in the positions of one quarter of that length. The shorter edges did in fact show a better measure of the uniformity of the power than the long edges in positions of a quarter of the length and up to one-tenth of the length of the angles approximately. The investigation of the combinations of two transducers has also been extended especially for the same quadrants and the adjacent ones with a transducer, for one in each long and short edge. A transducer may be in an optimal position along one edge for a single transducer, while the position of the other transducer varies along the other edge. For variations along the shortest edge, the preference for one of the aoorde positions with the coordinates of preferential locations of incorporated transducers is confirmed by an optimum measure of uniformity over a length of approximately six tenths. There are also almost as good positions to a length of three quarters and hardly less good in the positions of a quarter and a third. In addition, most of the positions, except those that are below one tenth from the angle, are better, similar, almost as good as or not much worse than those associated with the coordinates of the preferred built-in locations of the same quadrant . In the case of variations along the longer edge, the shorter edge transducer was placed approximately in the preferential position of six tenths, and a marked preference for combinations of adjacent quadrant locations was noted, with the best result just over under a fifth, and hardly better than that of the position 0.42 in a position of a third of the length and a result just inferior- in the position of a tenth. The quarter-length position is actually almost the same as for the middle position and the adjacent quadrant position of the coordinate of the preferred built-in location. It is evident that these procedures can be continued iteratively, and thus reveal more favorable combinations. Investigations performed with much lower rigidity panel elements based on the uniformity of the power output, showed peaks at the marginal locations of transducers, also around the built-in coordinate position but almost equally good at one quarter of the length of the edges of the panel, and were generally much less critical in terms of the position along the axes in terms of actual reached modal distribution. This would seem to be explained by the interaction between the rigidity of the lower panel and the compliance within the same transducer used. It seems that the resonant modal distribution of the panel is affected and altered by the location of the transducer, at least to some extent related to that location. A greater rigidity of the panel substantially avoids such effects. However, such internal conformity of the transducer and the possible interaction with the rigidity / elasticity of the panel are clearly another factor that must be taken into account, as well as its possible exploitation. The study of panel elements with a rather high rigidity and others with much less reveals, without a doubt, quite different results for the application of marginal excitation, including a greater or lesser criticality with respect to the locations of the transducers, go these individually or in pairs, and with respect to a greater or lesser interaction with the internal conformity of the transducer. Therefore, it is convenient to consider an intermediate stiffening panel element. For such intermediate stiffness panel elements, as expected, the differences with respect to the much smaller stiffness elements include an increase in the available acoustic power output by edge setting, a remarkably higher power for intermediate range modes and a more intense mode or peaks for the less frequent modalities. The tendency of the features of the stiffer elements preferably includes optimal individual transducer locations at edge positions on a coordinate of optimal locations for built-in transducers, and there is also feasibility at the midpoints and perhaps also at about a tenth of the angles. For two marginal transducers, the preferred embodiment indicates a related position coordinate of the optimal location of the built-in transducer, with inferior but probably viable results distributed to the middle and two-thirds positions and equality of some related quadrant coordinates and two-thirds positions of length. It is evident that the differences in the parameters of the materials of the panel elements beyond the basic capacity to sustain the bending wave are significant for determining the locations of the marginal transducers and that the use of two transducer locations or more, they produce highly individual solutions that require an experimental evaluation now possible based on these results. Also, at least for the essentially rectangular verified panel elements, it has been found that many of the edge locations or close to it, if not most of them, and probably all the inconvenient locations can be significantly improved (in terms of distribution of resonant modality dependent on the bending wave and excitation in acoustic response of the element) if they are associated with a charge of mass or fixation located in one or several marginal positions selected from the element in question. Other aspects of the invention, therefore, comprise the association of said excitation position with another marginal position of mass loading or level fixation of the panel element. With respect to the use of two or more transducers, exhaustive investigation of the combinations of marginal locations is not practicable, but indications are given on how to find the optimal location and other viable marginal locations for the second transducer given any marginal location of the transducer. first transducer. In fact, according to the indications of the present invention, other marginal locations of the transducers can be investigated and evaluated. Likewise, the use of localized marginal damping to improve the performance of any marginal transducer location can be studied and evaluated to any extent and depth, based on what is indicated in the present application, either to improve or reduce the contributions of some (s) resonant mode (s), either to deliberately interfere with another (s) resonant mode (s) or mainly to increase the output power. It was generally thought worth taking into account the fact that the lower resonant modes were related to the length of the longest natural axis of any panel element, and therefore that the longer edges of the panel elements were essentially Rectangular arrays were significantly more favorable to the location of the transducers, even to the location, if feasible, of the optimum position for operation with a single transducer. It is reasonable to see this fact as an application even when the use of another transducer is intended or recommended and also when it is intended to improve some resonant mode (s), deliberately interfering with other resonant modalities (s). ) or mainly to increase the power output. The fact that the range of operating frequencies of interest is part of the evaluation of locations for the transducer is also relevant as a general topic., since it can affect the optimal and viable locations, that is, the results could be different for ranges that are totally above or below them, such as 500 Hz. Another factor that can influence is the presence of an adjacent surface, behind the panel element, with a spacing that affects the acoustic performance. It is inferred or postulated that the nature of said preferred positions on the edge or adjacent to the edge tend to be announced in our previous PCT and other patent applications, which are usually considered as contributions for coupling to more frequent frequency modalities, with a more regular character than not, avoiding the dominance of a few frequency modalities. The convenience in question can be such, more for a lower total real vibration energy, than for a higher one, in the panel element, but high in terms of the population by frequency modalities, that is, more than "dead" in the sense of little or no coupling of some modality or few modalities.

BRIEF DESCRIPTION OF THE FIGURES The specific implementation of the present invention is illustrated in diagrammatic form and is described, by way of example in the attached figures, of which, Figure 1 shows an acoustic panel of distributed mode with a transducer of the type described in our previous PCT application; Figure 2 schematically shows four different implementations of marginal excitation or edge acoustic panels; Figure 3 shows the possible locations of the transducers in a marginal position in order to achieve the effects illustrated in Figure 2; and Figure 3A shows a transparent panel of this type; Figure 4 indicates four preferred marginal locations for the transducers illustrated schematically, with respect to the built-in location of Figure 1 which is shown in dotted lines; Figure 5 shows the same four preferred locations with respect to another preferred excitation built-in location and a preferred pair of the built-in complementary excitation location or dotted lines; Figure 6 indicates how the pairs of the four transducers in such preferred locations were connected for testing; Figure 7 shows pairs of viable but less preferred locations of marginally acting transducers; Figure 8 shows the position of angular excitation and advantageous mass loading in a preferred embodied action location; Figures 9 and 9A show four usually non-preferred locations of marginally acting transducers along with many other positions of mass loading or level setting and indicate how the test masses and the action transducers were associated with the panel; Figure 10 shows the area incorporated within the marginal positions for the transducer (s), the level-setting termination (s) and the elastic mount / suspension; Figures HA and B are output / frequency power graphics for an essentially rectangular panel element of fairly high stiffness and the transducers located along the shorter edges; Figures 12A and B are bar graphs related to uniformity measures of the output power; Figures 13A and B are output / frequency power graphics for two transducers, one fixed and the other with variant position along the shortest or longest edge; Figures 14A and B are bar graphs for uniformity measurements of the power output; Figures 15A and B are power / frequency output graphs and the output power uniformity bar graph for a much smaller rigidity panel element and a single transducer located along the longest edge; Figures 16A and B are power / frequency output graphs and bar graph of uniformity of output power for a second transducer located along the shortest edge; Figure 17 compares the power outputs with preferably incorporated transducers and transducers located at the edges for a panel element of low stiffness; Figures 18A, B and C show the effects of an acoustic screen (baffling), of a fixation on three edges and of both at the same time; Figures 19A and B are power / frequency output graphs and the corresponding bar graph of power uniformity for the low rigidity panel element with fixing on all three edges and transducers located on the fourth edge; Figures 20A and B are power / frequency output graphs and the corresponding bar graph of power uniformity for the low rigidity panel element with level clamping on two parallel edges and transducers located on another of the edges; Figures 21A and B are power / frequency output graphs and the corresponding bar graph of the power uniformity for the low rigidity panel element with fixation located at the angles / midpoints of the edge and transducers located on the other long edge; Figure 22 is a power uniformity bar graph for the low stiffness panel member with other located fixators located between the angle fixators / midpoints; Figures 23A and B are bar graphs for power evaluation without normalization for the low rigidity panel element with edge level fixation at seven points and the entire length of the edge respectively, and the position of another local fixer on the other edge in which the transducer does not have a favorable position; Figures 24A and B are power / frequency output graphs and the corresponding bar graph of the uniformity of the power for the case of fixing at the three edges evaluated with normalization; Figures 25A and B are power / frequency output graphs and the corresponding bar graph of the power uniformity for a panel element of intermediate stiffness and individual transducers located along the longest edge, with normalization; Figures 26A and B are power / frequency output graphs and power evaluation bar graph for the intermediate stiffness panel element with seven point fixation, evaluated without normalization; Figures 27A and B present the analogous cases with normalization for evaluation of power uniformity; Figures 28A and B are the power output graph and the power uniformity bar graph for the intermediate stiffness panel member and a second position of the transducer on the shortest edge; Figure 29 indicates a fixation of seven and thirteen points applied as indicated above; Figure 30 is a schematic diagram useful for explaining the impact of internal transducer compliance and Figures 31A-E are bar graphs of power efficiency for the panel element of low stiffness and different edge conditions.

DETAILED DESCRIPTION OF THE INVENTION In Figure 1, the loudspeaker 10 of the distributed-mode acoustic panel is in accordance with the description of O97709842 and the transducer means 12 has in the panel member 11 the optimum usual location near the center (although displaced of the) . The sandwich structure with a core 14 and liners 15, 16 is shown by way of example only, with many other monolithic and / or reinforced structural possibilities. In any case, the normal built-in location of the transducer potentially limits the available free area, for example, for the transmission of light in the case of a transparent or translucent panel. In resonant mode acoustic panel elements that are transparent or translucent, transparent piezoelectric transducers known in the art may be used, for example, titanium zirconate doped with lanthanum. However, this type of transducer is relatively expensive; therefore, the alternative approach that allows the acoustic panel element of resonant mode to be practically free and unobstructed is to optimize the design of the loudspeaker by choosing between four types of excitation as indicated in figure 2 directed to the margins or the perimeter of the loudspeaker. panel and labeled as T1-T4, which are described below: TI - refracts compression waves towards an edge (indicated as 18A) of the panel element 11 implementable by inertial-action transducers or excitation transducers related to the reference plane. T2 - refracts transverse bending waves along an edge (also illustrated at 18A) of the panel member 11 - implementable by lateral deflection of the edge of the panel by excitation transducers by bending action. T3 - applies a torsion to the panel element 11 as indicated by the angle between the edges 18A, B - implementable by the action of flexural or inertial excitation transducers. T4 - produces a linear deflection directly on an edge of the panel element 11 as indicated at the edge 18B - implementable in the local contact region by excitation transducers by inertial action. Figure 3 is a partial view of the composite panel 11 showing the high tensile strength coatings 15, 16 and the structural core 14 with the excitation transducers / drivers 31-34 for the four marginal excitation types T1-T4 / of edge mentioned above. In practice, less than four types of excitation can be used simultaneously in a panel, which can be conveniently optimized from the acoustic and mechanical point of view for the desired bandwidth and for the particular type of excitation used. Thus, an optimized panel can be excited by any of the different types of excitation or by several of them. A transparent peripheral excitation acoustic panel 11 can be monolithic, for example, glass or be formed by a coated structural core if a suitable translucent / transparent core and suitable coating materials are used, see Figure 11, with a viewing unit ( VDU) that allows the use of the screen as a loudspeaker; it can have a sufficiently high stiffness together with a small mass if it is composed of a pair of coatings 15A, 16A which enclose a lightweight core of airgel 14A with transparent adhesive I5B, 16B, as in a sandwich. Airgel is a highly porous solid material, for example silica. The transparent or translucent coatings can be formed by a laminated structure and / or made of transparent plastic material, such as polyester, or they can also be made of glass. Conventional VDU displays can be replaced by a transparent radiant acoustic panel of this type, even if the excitation is outside the main area of the screen without obstructions. A silica airgel material particularly suitable for the core is (RTM) BASOGEL from BASF. Other materials that can be used for the core could be lesser known materials that form aerogels, among them metal oxides such as iron and tin oxide, organic polymers, natural gels and carbon aerogels. A particularly convenient type of plastic coating laminate may be MYLAR polyethylene terephthalate (RTM), and other transparent materials of suitable thickness, modulus and density. A very high cutting module in aerogels allows to produce extremely thin composite materials suitable for miniaturization and other physically important factors, always working under acoustic principles of distributed mode. If desired, such a transparent panel could be added to an existing VDU panel, incorporating it for example as an integrated faceplate. In the case of plasma-type visors, the interior is maintained at a gas pressure close to the vacuum and has a very low acoustic impedance. Therefore, there will be a negligible acoustic interaction behind the sound radiator, which will improve performance and save the usual faceplate. In the case of film-type viewer technologies, the transparent front window can be constructed using a distributed mode radiator, while the display structure behind it can be dimensioned and specified to include acoustic properties that contribute to the propagation of sound from the front panel. For example, a partial acoustic transparency for the subsequent display structures will reduce the reflection of the back waves and improve the performance of the distributed mode loudspeaker element. In the case of viewers of the light-emitting type, they can be located on the rear surface of the transparent panel of distributed mode, without significant drawbacks for their acoustic properties, since the images are seen from the front. A transparent distributed mode loudspeaker can also have application in rear projection systems where it can be an addition to a translucent screen. This function can also be incorporated with a suitably prepared rear projection surface. In this case, the projection surface and the screen can be a single component, both for reasons of convenience and economy, but also to optimize acoustic performance. The back coating can be selected so as to take a projected image, or alternatively, the optical properties of the core can be chosen so as to respond to the projection applications. For example, in the case of a loudspeaker panel having a relatively thin core, it may not be necessary or ideal for full optical transparency, whereby alternative light transmitter cores may be chosen, for example, other grades or cheaper substitutes. The specific optical properties can be combined with the core and / or the surface of the coating to generate directional or brightness enhancing properties of the transmitted optical images. When the transparent distributed mode loudspeaker has an exposed front face it can be improved, for example, with the addition of pads or conductive regions, visible or transparent, for the user to input data or commands for the screen. The transparent panel can also be improved with optical coatings in order to reduce reflection and / or improve scratch resistance or anti-scratch coatings can be used. The core and cladding of the transparent panel can be chosen so that they have an optical dye, to achieve shades of color or neutral shades that improve the contrast rates of the viewer used in the loudspeaker of the panel of distributed mode or incorporated in it. During the manufacture of the distributed mode panel, invisible wiring can be incorporated, for example in the form of micro-wires or transparent conductive films together with indicators, for example, light emitting diodes (LEDs) or liquid crystal displays (LCD) or similar, which allows their integration into the transparent panel and its consequent protection, this technique also minimizes the damage to acoustic performance. Designs can also be achieved in which full transparency is not necessary, for example, in which a single panel covering has transparency to allow viewing of an integral viewer located below that surface. The transducers can be piezoelectric or electrodynamic according to the design criteria (including price and performance considerations) and are represented in Figure 3 as simple sketched elements adhered to the panel by convenient adhesive (s). In the case of an excitation of the aforementioned type TI, the inertial transducer 31 produces compression waves in the vertical direction in the panel 30. In the case of an excitation of the aforementioned type T2, the reflection transducer 32 works by changing direction to refract reflection waves through panel 30 of the loudspeaker. In the case of an excitation of the aforementioned type T3, the inertial transducer 33 serves to cause a deviation of the angle of the panel when driving diagonally and consequently over the entire panel of the loudspeaker. In the case of an excitation of the aforementioned type T4, another inertial transducer 34 formed by a block or with a semicircular shape serves to deviate from one edge of the panel 30. Each type of excitation will cause its own characteristic action in the panel 30, of which acoustic devices account in the global design of the loudspeaker that includes parameters of the panel 30 itself. The location of the transducers 31-34 along the edge of the panel is iterated in practice with the panel design parameters to obtain an optimal or at least acceptable modal distribution of the deformation waves. It is expected that, according to the characteristics of the panel, including the controlled loss, for example, and according to the location (s) and type (s) of marginal action on or near the edge, it could be applied to the panel 30 in question more than one audio channel, for example by means of multiple excitation transducers. This multi-channel potential can be increased by signal processing to optimize the sound quality and / or to control the sound propagation properties and / or even to modify the perceived separation between channel and channel and spatial effects. Particularly convenient locations of the transducers along the edges of an essentially rectangular panel are the locations obtained by orthogonal lines parallel to the sides or coordinates through an optimized or preferential built-in location according to the PCT application mentioned above, see the lines of points in 42 to 48 in Figure 4. It is actually practical to use transducers in at least two such locations related to the edges 45-48. Figure 6 shows serial and serial / parallel connections in the case of two and four transducers in A and B. Other connections that can often be preferred, including one-to-one direct connections to each transducer, and any conditioning of the transducer are feasible. desired signal can be applied, for example, differential timers, filtering, etc., to reduce unwanted interactions between the transducers and / or the source of the electrical signal. The preferred positions CP1-CP4 of Figure 6 refer to a built-in preferential location PL. Mating can be done from each coordinate, that is, CP1 and CP2, CP2 and CP3, CP3 and CP4, CP4 and CP1 and a preferred pairing is the one that conceptually defines the included area that is larger, in fact, it contains the geometric center x. Said conceptual area will, of course, pass through the usual or preferential optimal location of the built-in transducer or will contain it. See the complementary location CL and the indication in CP5 and CP6 for the first preferred pairing of excitation transducer locations. It is interesting to note that for a very high Q panel, the preferred and most preferred pairs of orthogonal coordinate excitation locations can produce a low frequency output that can be more widespread and uniform even than the preferential positions incorporated much closer to the center although there is some moderate variation in the frequency range more high The off-axis response is similar to higher frequencies, but strictly speaking, something more symmetric at lower frequencies. Figure 7 shows the results of an experiment where pairs of transducers were used for which a relatively orthogonal relationship was maintained centered on the normal incorporated preferential location of the transducer. Specifically, it is very advantageous for marginal excitation locations related to the SPI and SP4 coordinates, but the transducers are tested in positions translated relatively around the edge of the panel. The most viable / advantageous pairs of locations are indicated in the pairs of positions la, Ib to 6a, 6d. Figure 7 shows the results of another experiment in which the pairs of transducers were located at opposite ends of straight lines that passed through the built-in preferential points of location SPI, 2. Fewer viable / advantageous locations were found in positions 2a, 2d and 3a, 3d. It may be worthwhile to perform more experimental work relative to other pairs or other edge-dependent positions, and at present a theoretical systematization work is being carried out. It will be possible to appreciate from the dimensions cited measures in pairs of positions that provide viable / advantageous results measured / evaluated that Figure 7 is not strictly in scale. Figure 8 shows a panel structure 70 formed by a core 74 and liners 75, 76 having a transducer 72 mounted near the angle with a mass load 78 substantially in an otherwise normal built-in preferential transducer, which is actually placed or is part of the group furthest from the excitation angle by the transducer 72, which is particularly effective since it appears to behave as a "virtual" source of bending wave vibrations. It may be advantageous for the transducer to avoid a position with coordinates substantially centered at 5% distance from the angle, or at least to be coupled out of that position and it has been established that many resonant modes have nodes, i.e. low vibratory activity. Figure 9 indicates in schematic form an investigation on individual positions selected for mounting a transducer adjacent to the edge or located on an edge. See ST1-ST4 for positions in the angle, halfway to the side, a quarter of a distance on one side, three-eighths of distance on the side respectively; and selected positions for level setting / mass loading in edge positions on the panel. An excitation transducer was used, see 92 in Figure 9A with respect to panel 90, together with level clamps / fasteners by means of magnets with clamping jaw 93A / B. The performance or performance obtained using the position of the angle excitation transducer ST1 was improved by means of a mass load as indicated in Figure 9A at positions 13, 14, 18, 19, including further combinations with other positions. For the position of the excitation transducer ST2, the positions 6, 7, 8 and perhaps 9, 11 especially, 12, 15 together with other positions are suitable for a single mass caxga. The combinations 9 + 11 and 6 + 11 were particularly valuable, including further combinations. For the position of the excitation transducer ST3, the positions 5, 6, 7, 13 and especially the combinations 6 + 13, 10 + 13 and 6 + 18 and others are suitable for a single mass load. For the position of the excitation transducer ST4, the best positions appear to be 6, 18 but none of them was compared to those corresponding to the other positions of the exciter ST1-ST3. Figure 10 shows a panel loudspeaker 80 having an incorporated unobstructed region Sl, which extends through preferential and normal transducer built-in locations and beyond, and a marginally located transducer S2. The region Sl can fulfill the purpose of viewing directly, or represent something ported by the panel 80 without affecting the acoustic performance, or something behind which the speaker panel 80 passes, in a narrow space and / or in transparent or translucent Both volume and quality are easily improved. The volume is increased by adding reasonably located additional transducers (not shown in the figure). The quality is improved by level fixers located at the edges 83, convenient for controlling certain modal vibration points effectively as panel termination (s). It is also indicated the panel 80 with localized elastic suspensions 84 located in neutral form or even benefiting the achieved acoustic performance. The high-pass filter 85 is preferred for the input signals to the transducer (s) 82, to conveniently limit the optimum reproduction range, for example, not less than 100 Hz for panels of A4 size or the like. Therefore, there should not be any low frequency vibration of the panel / exciter. It is advantageous in terms of acoustic performance to control the acoustic impedance in the panel 80, so that it is relatively low in the marginal or peripheral region, especially in the vicinity of the transducers 82 where the surface velocity tends to be high. Among the benefits derived from such control, significant light is included for the flat elements (approximately 1-3 centimeters) and / or grooves or other openings in the adjacent peripheral frame or support or grid. It is also feasible and advantageous to provide a deliberate means, such as mechanical damping, to achieve the acoustic modification including loss in the area 81, or even marginally, so as not to obstruct, at least in the case of higher frequencies. This can be achieved by choosing the materials, for example, monolithic or acrylic polycarbonate and / or a suitable surface coating or laminated construction. The resulting effective concentration of acoustic radiation to the marginal regions in the vicinity of plural transducers facilitates particularly the reproduction of several sound channels, at least for listening in the near field, as it happens in the case of computer games or similar applications. of virtual sound located. Further, the combination of multiple activated sound sources is not necessarily problematic when added together, at least for such visual audio presentations. The following table indicates the most important physical parameters of real panel elements used for the research referred to in Figures 11-28.

Figures 11 to 14 refer to the upper stiffness panel element of the second column, Figures 15 to 24 to the much lower stiffness panel member, and Figures 25 to 28 to the intermediate stiffness panel element of the third. column. All graphs have the acoustic output power (dB / W) as the ordinates and the frequency as abscissa, thus they show the acoustic output power measured as a frequency formation, usually as a dotted line actually plotted. Most graphics also show a superior setting of the true power line. As mentioned in the preamble, this adjustment is made by applying functions that are normalized until reaching a straight line, and allows the evaluation of the free resonant mode of the frequently found effects of the power drop at lower frequencies. It has been found that uniformity in power contributes significantly to the quality of sound. From this normalized value of the actual power / power output, it is advantageous to produce an evaluation of the uniformity by the inverse of the mean square deviation and most of the bar paths are of that type. The upper stiffness panel element for Figures 11 to 14 is actually somewhat less rigid than that used for Figures 7 and 9 above, but clearly shows the preference for simple transducers to be located in the positions corresponding to the coordinates of embedded transducer locations previously established as optimal, ie, at approximately 3/7, 4/9 of the length from any angle or approximately 0.42-0.44. However, there are advantageous potential location intervals between such positions for each edge and beyond them, actually within about 10% and 15% in the middle regions of shorter and longer edges, respectively, and also within 28% and 30% in quarter-length positions. At least for the most part, the test positions for location near the edge or edge of the transducer are based on the spacing that substantially corresponds to the difference between the preferential coordinate value of 0.42 for the location of the incorporated transducer and the midpoint (0.5) of the edge, although with a greater number of alternating spaces increased to 0.09. The usual test locations are then 0.08, 0.17, 0.28, 0.33, 0.42, 0.50. In general, it is believed that the illustrated graphic and bar graphs are substantially self-explanatory in terms of showing the best and presumably advantageous locations for the transducers, and for locating as far as possible to improve the locations of less advantageous transducers. , see Figure 23. Regarding the location of the near edge or the edge of the individual transducer, the other two verified panel elements of intermediate rigidity and much smaller also show the same preference of incorporated coordinates based on the power uniformity, see Figures 15 and 25. However, the lower stiffness panel element shows another band of almost equally advantageous locations ranging from about one quarter to less than one tenth of the length from the angles. Interestingly, if the estimate is based on the efficiency, that is, the amount of power emitted - as would be the case for a mean line through the true plot of the power output that was the base used for the mean square deviation - the aforementioned band is distorted to reinforce the quarter-length position and is mainly preferential for the related incorporated position of the coordinate, see bar graph of the inverse-mean square deviation of Figure 31A. The panel element of intermediate stiffness is modified to the feature of the panel element of superior stiffness by showing an advantageous interval between the incorporated positions of preferential coordinates, but also shows advantages in the positions of the length of a tenth approximately. From the inspection of the real output power paths, the technology experts should appreciate that there are differences between the viable and optimal transducer edge locations, in terms of the impact on the expected quality of sound reproduction - for which modality is usually taken as an important factor, that is, the number and uniformity of the excitation of the resonant modes. If characteristics such as, for example, the modality are seen as more advantageous for the locations indicated as preferential based on the evaluation of the uniformity of the output power, it is, of course, feasible to process the input signals towards what it is then shown above normalization - specifically selectively to amplify the low frequency in a signal conditioning or equalization foxma. This would achieve and actually exceed the available power using optimized locations in terms of efficiency; but obviously not the efficiency itself, because more input power must be used. Accordingly, other ways of increasing the lower frequency power, as previously indicated, were investigated either by means of an acoustic screen and / or by locally spaced selective fixation, or by means of the total edge setting. Figures 18 A, B, C indicate an increase that is generally beneficial from the lower frequency output for an acoustic screen with a coverage area of more than 60% higher than that of the lower stiffness panel, the rigid fixing of the three edges do not reach the location of the transducer and both said acoustic screen and said fixation. This acoustic screen tends to maintain the modality but it may not always be feasible in specific applications. Therefore, the complete investigation on the fixation would appear useful for the alternative transducer edge locations for the lower stiffness panel element. The results showed that the evaluation of the effectiveness tended to emphasize the point of the quarter of the length, so much for the fixation of complete edge in the parallel edges or three real edges, as for the fixation of local edge of 7- point in the angles and midpoints as in "X" in Figure 29, with the edge of the location of the transducer without attachment along its length, see the bar diagrams of Figures 31 B, C and D, respectively. However, the fixation at point 13 as in "X" + "or" in Figure 29 completely changed the emphasis towards the built-in position of the preferential coordinate. The evaluation of the elements of the panel with the fixation based on the uniformity of the power produces almost the same results as for the indication of the best locations of the transducer, see the graphs of baxxas of Figures 19 A, 20 B, 21 B and 22, but with important differences with respect to the following favored positions, which is confirmed, in general, by the inspection of real output power paths. In fact, a particularly strong gene-wide correlation was found between the preferences through an inspection carried out by experts and the evaluation according to the uniformity of the power output. In turn, this tends to confirm, at least, a slight preference for such evaluation, unless there are practical factors that lead to the preference for effectiveness rather than quality, although, in any case, this may not be so different. . Another application for localized edge fixing is in relation to improving a non-advantageous transducer edge location, see the bar diagrams of Figures 23 A, B showing the right side instead of the left sides of the edge in question, unlike the drawings. The cases in question refer to the panel element of lower stiffness and are fully fixed by three edges and seven fixing points, with a localized fixator that varies along the same edge as the transducer means. In both cases, a useful improvement results approximately in the quarter-length position from the angle furthest from the exciter - see the reference bars on the right side of Figure 23 B for the condition without fixation. The interval is greater for the case of total edge fixing, see Figure 23 A. When there is a difference between the evaluations of power efficiency and power uniformity, it is convenient to take into account that any element of the panel with fixing of angles to the edge with which the transducer is related, effectively has null values forced into the angle. Therefore, there must be up to half the wavelength distance for the resonant modes in question before the vibratory activity can reach the anti-modal peaks. If the preference for a nearby transducer location is indicated - to the angle through the evaluation of the uniformity of the power, should be treated with caution because it could have low power / efficiency, even though it is uniform because it is connected to all the waveforms of the fully resonant mode in question, possibly, in small increases in their waveforms. Therefore, it is recommended to carry out the verifications with the corresponding evaluation of power / efficiency. In fact, the best case occurs when there is a substantial possible match "between the two bases of evaluation, or a certain commitment particularly adapted to a specific application and preferably, taking into account also the experienced inspection of power graphics / Frequently perhaps in an advantageous way with and without any normalization for the purposes of the evaluation.For the panel elements investigated with superior and intermediate rigidity, there is a considerable measure of consistency in terms of the best edge locations of the transducer, but with a difference quite marked with respect to other advantageous locations The very lower stiffness panel element is markedly less critical in terms of the advantageous transducer edge locations.This position is even more evident when considering the use of more than one transducer means related to edges of the same panel element.The position for the largest aco The resonance of a panel element is accompanied by the complexity of its inevitable interaction combined with the natural pattern of distributed resonant vibration of the panel element and composed of that distributed vibration pattern being implementable only at the edges of panels. There are notable variations of simple rules such as those based on the established preferential location coordinates of the built-in transducer. However, the evaluation procedures of the present reach variable tools to find good combinations of transducer locations related to the edge. For the upper stiffness panel of the above Table, Figures 13A, 14A a transducer means is located at a position within the tolerance range of about 0.38-0.45 for the preferred position 0.42 for the transducer means simple along the longest edge. The second transducer means varies along the nearest shorter edge and Figure 14A shows marginal preference for the preferred position 0.42 furthest, ie centered at 0.58, compared to several other positions in approximately one quarter, a third and two thirds of length from the common angle. It is interesting to note that, to fix the second transducer means in said preferred position of approximately 0.58 along the shorter panel edge, and to vary the other transducer along the longer panel edge (see Figures 13B, 14B) , produced the best and the next best preferences at approximately the positions of one fifth (0_, 17) and one quarter of the length along the longest panel edge, both proving to be better than the initial position (approximately 0, 42) for the uniformity of the power. This is a procedure that can clearly have a greater application in a repetitive way, although it is recommended that either or both be carried out, both the evaluation of power / efficiency, and the experienced inspection, especially if there is no convergence of location in the procedure or if any good position indicated is less convenient in practice than expected (or it was earlier in the procedure). Figures 16 A, B show the results of the investigation of the much smaller rigidity panel element with the preferred transducer location at approximately 0.42 used for the longest edge and a second transducer that varies along the shorter edge and closer. There were no great differences in the increase in the uniformity of the power, finding the three best approach angles and the preferential position closer to 0, 42, with some other general preference for associations in a certain quadrant. The same investigation for the intermediate stiffness panel element showed a strong preference for the adjacent location of the transducer at 0.42 preferential in the quadrant (in fact, 0.58), see Figures 28 A, B. Returning to the case of much less rigid panel element, two effects that contribute to a position of the exciter much less well defined, optimal, quasi-optima are observed. One of them is that the panel modalities for the optimization frequency range are higher than for the more rigid panel elements. The panel element is, therefore, a closer approximation to a continuity and the uniformity of the output power is less dependent on the position of the transducer, in particular, on the positions of the second transducer. The other effect refers to the mechanical impedance much lower than the panel element, which leads to a much lower dependence on the position of the transducer for energy transfer. The mechanism in question is explained below. The mechanical impedance (Zm) of a panel element determines the resulting movement in the case of a force applied to a point, see 100, 101 in Figure 30. An object related to the panel with a mechanical impedance but much smaller, even almost comparable with the impedance of the panel, it will move to a large extent from the movement of the panel, where the object is located. Relate an exciter transducer of the type of mobile coil with the panel is equivalent to connect the panel with a mass with ground (the cup-shaped magnet of the transducer, see 102) through a spring (the suspension of the coil that produces the voice of the transducer, see 108). When the impedance of said spring is very close to the impedance of the panel, it will determine to some extent the movement of the panel in the transducer. In the limiting case that this spring totally determines the movement of the point in the transducer, there would be no dependence on the input power at the position of the exciter. In practice, the proportions of the impedance of the spring to the impedance of the panel can greatly affect the best location of the transducer, and the results are no longer so clear for the optimal / quasi-optimal transducer locations. This low mechanical impedance has more effect on the location of the edge transducer than on the location of the built-in transducer because the mechanical impedance is still lower at the edge of the panel, which means that a transducer, with the coil that produces the time in suspension , has a greater effect. Specifically, for the lower stiffness panel of the previous table: the mechanical impedance in the panel body is Zmbody = 2, 7 Nspf1 the mechanical impedance at the edge of the panel is approximately half Zmbody, that is, Zrriedge = 1.3 Nsm "1. The elasticity of the suspension of the voice spring of the transducer used is: Cms = 0.52 x 10" 3 mN "1. The mechanical momentum at each of the modal frequencies can be an order of magnitude less than average impedance, Zmedge • By 1 ° both, it is feasible to estimate a typical frequency, below which the exciter has an intense effect on the panel element, ie where the impedance of the voice spring suspension is approximately fifth of the average impedance at the edge of the panel. ? xCms and gives an estimate of 1200 Hz, below which the transducer and the panel are intentionally connected, which is within the optimization frequency range. Considering the transducer and such low mechanical impedance, the panel element as a connected system, the transducer determines, in part, the impedance of the panel element, and the uniformity of the output power is less dependent on the position of the transducer. Repeating this analysis for the high stiffness panel offers a corresponding frequency of 130 Hz, which is outside the optimization frequency range.

Claims (32)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property; An active acoustic device comprising a panel element having a distribution of resonant modes of bending wave, a transducer, for the excitation of the resonant modes of bending waves, coupled to the panel element in a marginal position of the element of panel adjacent to an edge, characterized by at least part of the edge of the panel member being fixed, so as to cause an acoustically acceptable action dependent on said distribution of resonant modes of bending wave.
2. Active acoustic device according to claim 1, wherein at least one edge fixing element is provided for fixing the edge in at least one discrete location.
3. Active acoustic device according to claim 2, wherein the location of the edge fixing element is arranged to improve the acoustic performance of the device together with the transducer means located in a marginal position which is not itself selected for a optimal functional interaction with the panel element.
4. Active acoustic device according to claim 2, having a plurality of edge fixing elements in a plurality of discrete locations for fixing the edges.
5. Active acoustic device according to claim 3 or 4, wherein the panel member has a multi-sided shape and the edge fixing element is associated with more than one face.
6. 6 Active acoustic device according to claim 5, wherein the panel member is substantially rectangular and the multiple located edge fixing elements that are associated with three faces are not associated with the transducer element.
7. Active acoustic device according to claim 6, wherein the multiple located edge fixing elements are at each angle and at the intermediate points of said three faces.
8. Active acoustic device according to claim 1, wherein the edge fixing element extends along the edge of the panel element.
9. Active acoustic device according to claim 8, wherein the panel member has a shape with multiple faces and the edge fixing element extends along at least one face not associated with the transducer element.
10. Active acoustic device according to claim 9, wherein the panel element is substantially rectangular and the edge fixing element extends along two parallel faces.
11. Active acoustic device according to claim 9, wherein the edge fixing element extends along three faces.
12. Active acoustic device according to any of the preceding claims, wherein the edge fixing element comprises a mass loaded on the panel.
13. 13. Active acoustic device according to any of the preceding claims, further comprising a second transducer located in a marginal position of the panel adjacent to an edge.
14. Active acoustic device according to claim 13, wherein the panel member is in the form of multiple faces and the transducer element is associated with at least two side edges.
15. 15. Active acoustic device comprising a substantially rectangular panel element having a distribution of resonant modes of bending wave and longer and shorter faces, a first transducer, for the excitation of the resonant modes of bending wave, coupled to the panel in a marginal position along a longer face, and a second transducer, for the excitation of the bending wave resonant modes, coupled with the panel in a marginal position along a shorter face.
16. 16. Active acoustic device according to any of the preceding claimsG. , wherein at least one marginal position separates away from the nearest angle along the corresponding edge.
17. The active acoustic device according to any of the preceding claims, further comprising an acoustic screen extending around and beyond the panel member.
18. 18. Active acoustic device according to any of the preceding claims, wherein the panel member is at least partially transparent or translucent.
19. 19. Active acoustic device according to any of the preceding claims, wherein the transducer element is electromechanical type.
20. An active acoustic device according to any of the preceding claims, wherein the transducer element excites the bending waves in the panel, by at least one of the following actions: exciting compression waves at the edge of the panel member; deflect the edge of the panel member laterally to excite transverse bending waves along the panel member; apply torsion through an angle of the panel element; and producing linear deflection of a local edge region of the panel member.
21. 21. Active acoustic device comprising a panel element having a resonant bending wave distribution, a transducer coupled to the panel at a marginal position of the panel adjacent to the edge, characterized in that the transducer is spaced apart from an angle by a distance between 0.32 and 0.5 times the length of the edge.
22. 22. Active acoustic device according to claim 21, wherein the panel member has a rectangular shape with longer and shorter edges.
23. 23. Active acoustic device according to claim 22, wherein the edge is a shorter edge and the transducer is spaced apart from an angle by a distance between 0.38 and 0.46 times the length of the edge.
24. 24. Active acoustic device according to claim 22, wherein the edge to which the transducer is adjacent is a longer edge.
25. 25. Method for manufacturing an acoustic device that includes a panel element having a distribution of resonant modes of beneficial bending wave action for acceptable acoustic performance together with the transducer element properly coupled to the panel element, the method comprising: adding elements localized fixation to improve the acoustic performance resulting from some of the particular transducer elements, located marginally, evaluate the acoustic performance that results from locating the fixation elements located in several different marginal positions of the panel element, and select a marginal position for a acceptable acoustic performance and fix the fixing elements in the selected marginal position.
26. 26. Method according to the claim 25, where the evaluation of the acoustic output is limited to a range of frequencies relative to the intended use and to the acceptable performance of the active acoustic device.
27. 27. Method according to claim 25 or 26, wherein the evaluation is made on the active acoustic device that functions as a sound radiator or loudspeaker and in relation to its acoustic output, using the different marginal positions.
28. 28. Method according to claim 27, wherein the evaluation of the acoustic output includes evaluating at least one of the various resonant modes, their frequencies, their distribution and the uniformity of their contributions to the acoustic output.
29. 29. Active acoustic device comprising a panel element having a distribution of resonant modes of bending waves, a panel transducer coupled to the panel element in a marginal position of the panel element, characterized in that: a mass load or a fixation in a driving location, spaced apart from the edge, and in a preferred location to provide a driver for coupling bending waves in the panel.
30. 30. An active acoustic device according to any of the preceding claims, wherein the marginal position is selected for an optimum or better functional interaction of the transducer element, as it is located, with the panel element, in terms of numbers and frequencies of the resonant modes involved in the operation of the transducer element together with the panel element.
31. 31. Active acoustic device according to any of the previous claims, wherein said marginal position is selected for an optimum or better functional interaction of the transducer element, as it is located, with the panel element, in relation to the power of the acoustic output as an acoustic or loudspeaker radiator.
32. 32. Active acoustic device according to any of the preceding claims, wherein the marginal position is selected for an optimum or better functional interaction of the transducer element, as it is located, with the panel element, with respect to uniformity of the power of the acoustic output, such as an acoustic radiator or loudspeaker.