SK14552000A3 - Acoustic device relying on bending wave action - Google Patents

Abstract

Acoustic device comprising a member relying on bending wave action with beneficial distribution of resonant modes thereof, wherein the member has its acoustically active area at least partly bounded by means having a substantially restraining nature in relation to bending wave vibration. Operation can be below coincidence, or above if desired for active acoustic device further having beneficial location of bending wave transducer means determined with reference to and taking account of such bounding means.

Description

Technical field

The invention relates to acoustic devices which comprise an acoustic radiator based on the operation of bending wines and the resulting surface vibrations producing an acoustic output.

BACKGROUND OF THE INVENTION

US-A-3,247,925 to WARNAKA discloses a low-frequency loudspeaker consisting of an extremely rigid panel whose outer edges are bolted or bonded to a rigid frame that carries a conventional voice coil transducer that transmits the bending power to the center of the panel. This low-frequency loudspeaker device is said to operate completely above the coincidence frequency of the wines.

Also known from US-A-596,733 in the name of BERTAGNI is a loudspeaker having a membrane formed by a cellular face of expanded polystyrene with a bias front and back of irregularly shaped or irregularly shaped.

The inventive explanation relating to acoustic bending-based acoustic devices, generally considered to be resonant-type panels, is given by International Patent Application WO97 / 09842, which includes improving or optimizing acoustic properties according to panel parameters, including geometry and bending stiffness, which in particular, it includes traffic advantageous at or below the coincidence frequency. The relevant geometric parameters include the proportions or aspect ratios of the panels as such, including the panels that are used as passive acoustic devices. The flexural stiffness (s) parameters may preferably be

• ·

Even in interaction with geometric parameters, including their anisotropy, for example, to varying bending stiffness or may be decomposable on the main constant along the axis of the geometric shapes involved, for practicable variations in the ratios of such shapes. Preferred locations of the transducers of the active acoustic devices inside the panel member have preferred, limited, coordinates. Other surface stiffness distributions of the bending stiffness may advantageously contribute to providing additional advantageous positioning locations for the transducers, for example at geometric centers and / or center of gravity, see International Patent Application WO98 / 00621, including the combination of the aforementioned bending operation with another acoustically relevant piston action. Acoustic operation is described and claimed at least in International Patent Application WO97 / 09842, both for the whole panels and for the acoustically active parts thereof.

Based on intuition, our specific analysis and design methodology for such acoustic devices, which are based on the principle of bending wine operation, has mainly been focused on whole panels whose edges are completely or substantially vibration free, including lightweight edge damping. The present invention is based on the surprising results of other contraintuitive considerations, research, and experiments.

SUMMARY OF THE INVENTION

Certain essential requirements are still in use and have a profound technological-inventive significance, especially for a member of an acoustic device that extends transversely of its thickness and is capable of retaining bending waves in its logically resulting, acoustically active region, i. the essential requirement for which it is referred to herein as a resonant acoustic member or panel, and for such parameters as geometric parameters and bending stiffness to be constant values resulting in a natural vibration distribution by the bending wines of said member which is effective or advantageous to achieve required or acceptable acoustic operation of this equipment above the frequency range, ie another request for a resonant acoustic member or panel of the present application. In particular, embodiments of the present invention provide means that provide substantial limitation of the vibration of the bending wines, typically at the edges, at the periphery, or other peripheral portions of such a member or panel, or an acoustically active region thereof, and which are further typically capable of operating at least partially below the coincidence frequency. The term "substantial limitation intentionally includes a greater limitation of the portion (s) of the edge (s) of this member, as specifically disclosed in patent application WO97 / 09842, in particular the margin of the effective load, anchoring, or the effectiveness of the principal effect.

There are two views, effects, or inventive aspects that seem to be beneficial for judgment, and which relate to such substantial marginal and areal, boundary and circumferential constraints.

One view is that limiting and reducing the available bending wines of the vibratory, marginal, circumferential and boundary movement of the member (as compared to the specific description in WO97 / 09842) can create an advantageous composition of the achieved acoustic output from the vibratory bending wines back to the acoustically active area. The second view is that the acoustically relevant and effective modes of action of the resonant bending wines will be different (compared to the specific description in WO97 / 09842), in order to limit and suppress the vibrational movement of the bending wines at the edge (s), perimeter and boundaries of this member, thus effectively reducing and eliminating the benefits of the lowest resonant modes that would be active if the edge (s), perimeter, and boundary of the acoustically effective region of this member were equally free of bending wines as specifically disclosed in WO97 / 09842; and there is a reduction and a substantial suppression of the resonant modes augmented by the twist.

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As a result of less numerous or less rich resonance content simplified acoustically active resp. The relevant bending modes can be given as an example for analogue and analysis based on equivalent single beams, taking into account the interactions with respect to the inclusion of resonant plate modes starting with respect to each beam at the frequency of resonant modes f rather than fO , and "lost combinable modes including frequencies f0, but with interesting and useful effects available with respect to uniformity of distances of directly or combined resonant modes including frequencies fl.

There are numerous branches, and may be advantageous, including the achievement of improved acoustic energy conversion efficiency and / or often very advantageously an increased range of candidate sub-regions for feasible and optimal transducer positions, at least as determined by the mechanical impedance analysis of the International Patent Application and / or typically to a much greater extent of the feasibility of planar shapes and proportions of said members, as exemplified in the examples for isotropic bending stiffness, just about 1: 1 to about 1: 3 and greater, and / or feasibility of acoustic performance for panel member materials. a lower intrinsic bending stiffness at least as an effective overall reinforcement by contributing from its peripheral, circumferential and boundary constraints, and / or the capability of a high power loudspeaker member for making the loudspeakers, all included, when such a restriction may provide substantial load, whether the inertia of the base, or as further practiced, real attaching to a stiffer and more robust support or otherwise for large loads.

deals simultaneously with PCT / GB99 / 00404,

An important advantage of the present invention is that new and advantageous acoustic devices with a resonant panel are provided, including active acoustic devices such as loudspeakers, with significant levels having a robust level with respect to and described in between simplifying the manufacture of such type of devices especially on higher acoustic devices specifically shown in the national patent application WO97 / 09842.

According to one aspect of the present invention, an acoustic device is provided based on bending operation which is operable below the coincidence frequency and comprises a member providing said acoustic operation because of the advantageous distribution of resonant modes of bending operation in the apparatus, the member having its acoustically active an area at least partially enclosed by means having substantially restrictive properties with respect to vibration of the bending wines.

According to a second aspect of the present invention, there is provided an active acoustic device comprising a bending wound member having a preferential distribution of its resonant modes and a preferred method for positioning the bending waveguide, the member having its acoustically active region at least partially delimited by means having substantially limiting properties with respect to vibration of the bending wines, and this method of positioning the transducer is defined with respect to said bounding means, taking into account these bounding means.

The total perimeter of the acoustic member of the device, or only a portion thereof, smaller than the entire perimeter of the member may be substantially constrained or fixed, for example, a rectangular panel may be constrained or mounted on one or more or all of its side edges. This may be useful as a flag mounting providing said substantial restriction on one side with an acoustically active region extending therethrough, or as a mounting on two sides that may be parallel and may provide said substantial restriction with the acoustically active region between said mounting and

¹ limiting sides and a closed or only loudspeaker with diaphragm, frequency devices, the diaphragm makes it possible to manufacture a baffle to handle radiation that would otherwise be low frequencies.

can facilitate production to highly selective for example when medium / high completely or almost completely closed the so-called loudspeaker with infinite and control of the reverse acoustic could be detrimental at medium to fully vented

The solid, substantially limiting or clamping frames also allow the construction of a loudspeaker group that will be more predictable in a mechanical sense, together with facilitating the manufacture of a loudspeaker group having a relatively robust construction (compared to a resonant panel loudspeaker where the panel edges are substantially free or are hung only in a slightly damping manner).

Substantial restriction or attachment of the peripheral portion (s) or edge (s) of the acoustic member may be achieved in any desired manner, for example, the edge (s) to the thick frame by adhesive or mechanical means, including, for example, securing the desired edge (s) between the frame members. Restriction or attachment of the desired edge may also be achieved by a casting technique (such as injection molding of plastic materials) by providing the edges of the member with integrally or integrally reinforced peripheral portions with sufficient stiffness to restrict movement of the edges of the acoustic measure. Such casting techniques may be particularly suitable where the acoustic member is formed in one piece and can be easily achieved in an economical manner.

immediately or in some way by fixing a similar member. As acoustic

A substantial restriction or fixation can also be used to define one acoustic member within another, larger one.

• • • • • • • • • • • • • • • • • • Such a large acoustic panel designed to operate at medium or low frequencies may be cast such that it includes a smaller acoustic panel designed to operate at high frequencies and is defined by intermediate reinforcing ribs.

The operation of a substantial limitation or mounting may be intended to achieve a mechanical termination impedance designed to control the reverberation time in the acoustic member, as an aid to control the frequency response of that member, possibly especially at low frequencies.

The proportions of suitable panel members may be the same as in the specific explanation of patent application WO97 / 09842 or may be substantially different due to variations in individual shapes. For example, substantially rectangular resonant panel members with an isotropic bending stiffness could have aspect ratios of less than 1: 1.5 as generally described in the prior art explanation for panel members with substantially free edges, without limitation to such members, such as described herein in greater detail, or greater than 1: 1.5, as also described in detail herein. Changes in anisotropy and complex distribution of flexural stiffness (s) are expected, as mentioned above.

The bounding means may be arranged at least partially or definitively around the acoustically active region and / or around the peripheral edges of the panel member to be completely acoustically active, typically in the range up to 25% or greater of the peripheral edge region, often the entire range.

Resonant panel members are generally self-supporting and would not require overvoltage for mechanical stability, especially for use with free-edge or single-edge-hanging types.

The fixed panel members are about an approximately ten-fold increase in the first bending frequency due to the natural rigidity of the fixed panel member. It is logical and practical to substantially reduce the bending stiffness properties to reduce the first modal frequency and previously the lower frequency range. It is believed that the stiffness of the panel member in such a case may already be about 0.001 Nm (Newtonmeter), and the density range already about 25 g / m ² .

In one aspect, these limits of values describe a panel member which, for mechanical stability and the function of suspending the excitation members, may benefit from the application of tractive forces. These forces may be applied uniformly or differentially, i. in different directions and / or at different stresses due to the effective geometry of this member.

Within these limits, the stretched panel exhibits a high ratio of the properties of the stretched bending wool layer and having predominantly second order or undistributed activity of the wines (constant speed with frequency). For such a "panel member", the resonance distribution can be optimized for the desired acoustic waveform by controlling the voltage and boundary geometry, in broad agreement with the explanation of the distributed modes, see WO97 / 09842. Also, the advantageous mode distribution into the operation of the transducer can be further enhanced by the advantageous and optimized positioning of the exciter and sensor.

Depending on the degree of tension and with the increase in density, especially the bending stiffness, there will be a range where the activity of the second order bending wines is overlapped and extended by the fourth order of diffused bending action due to the stiffness. Optimization of these two factors can be derived by calculation and / or experiment to obtain the best results in a given application.

The supposed area of construction is smaller acoustic panels with fixed edge and wide bandwidth.

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BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by way of example with reference to the accompanying drawing, in which: FIG. 1 and IA, a resonant, general rectangular panel acoustic member 10 is shown in exploded, perspective and sectional view mounted at its edges between peripheral frame members 11A, 11B, using screws and nuts 12A, 12B that may further be suitable for attachment to supporting frame or other basic structure. In FIG. 2 shows an alternate fastening and edge ending of the resonant panel acoustic member 20 by attachment to the frame 21 with an adhesive 22. 3 and 3A are a partial perspective view and sectional view of an injection molding 35 formed as a wall member, provided with reinforcing ribs 36 that intersect the rectangular frame 31 as a limiting edge of the acoustically active panel surface 30, wherein the frame 31 is also formed with protruding ribs which reinforce the edges of the operating panel surface 30. In FIG. 4 is a partial perspective view of a resonant panel acoustic member 40 stretched over the frame 41 and secured at its edges by a peripheral clamping frame member 42. FIG. 4A is a partial cross-sectional view of the embodiment of FIG. 4. In FIG. 4B is a partial cross-section similar to FIG. 4A, an alternate embodiment of a resonant stretched panel acoustic member is shown. In FIG. 5A, B are graphs depicting the frequency response of respective panel members having dimensions A4 and 4, respectively. A5, where the thick lines represent a panel fastened by the edges and the weak lines represent a panel with free or resiliently hinged edges. In FIG. 6A, B, 7A, B, and 8A are frequency-dependent graphical representations of mechanical impedance for selected aspect ratios of fixed-edge panel members. In FIG. 9A, B, C are graphical representations of the respective continuous inverse mean squared deviation of the transducer locations. In FIG. 10 is a diagram of calculated mechanical impedance for a single panel member

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9

999 9 9 • 9 9 9 9 • Fixed edge, quarter panel. In FIG. 11 is a graphical representation of the various aspect ratios of the fixed edge panel. In FIG. 12A to 12H are respective diagrams of the measured quarter panel mechanical impedance for different aspect ratios. In FIG. 13A-H are respective diagrams of the acoustic output adapted to the reference value. In FIG. 14 is a diagram showing maximum inverse mean squared power deviation for different aspect ratios. In FIG. Figs. 15A-J show combined polar acoustic output diagrams for lower resonant modes, at a 1: 3 aspect ratio of a fixed-edge panel member. In FIG. 16A-D are comparative acoustic output power diagrams for specific panel structures that differ in dimensions and / or stiffness.

DETAILED DESCRIPTION OF THE INVENTION

The acoustic member of FIG. 1 and 2 may be and is shown as a general rectangular member and may have an aspect ratio considered to be advantageous in WO97 / 09842, although much larger aspect ratio ranges will prove to be a beneficial potential within the general goal of obtaining a high mode density and uniformity of mode extension in this member.

In FIG. 4A illustrates one embodiment of a resonant acoustic member 40 stretched over a rectangular frame 41 and secured at its edges to a rectangular peripheral frame 41 by clamping frames 42 to keep the acoustic member 40 in place. A tensile force is applied to this member 40 in the direction of the arrow F. As an alternative embodiment, as shown in FIG. 4B, the clamping frame 42 may be replaced by tensioning means 43, including, for example, tensioning springs 44 on the frame 5, where the tensioning means 43 are secured to the edge of the acoustic member 40 to tension the member 40 over the rectangular peripheral frame 41.

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In the acoustic members in the embodiment according to FIG. 4, 4A and 4B, vibration exciters, for example of the type described in WO97 / 09842, may be positioned to generate resonance in the acoustic members and to provide an acoustic output so that the acoustic members may function as speakers or loudspeaker drive units. These vibration exciters are not shown in FIG. 4, 4A and

4B.

Strong limitation or gripping of panel edges allows the use of relatively low stiffness material (as compared to conventional practice for panels with substantially free edge), which can help reduce the base frequencies of panel bending modes, even below the levels typically found for typically stiffer panels with substantially Free margins (and in spite of the actual loss of the lowest frequency modes in the free margins with the panel fully attached). For example, in the case where the stiffness range for a practical example of a panel with free edges described in WO97 / 09842 may be of the order of 0.1 to 50 Nm, the rigidity of the panel with fixed edges of the same general type may be at least in the order of magnitude. may even be as low as about 0.001 Nm. Also, when the surface density range of said practical example of free-edge panels may be 100 to 1000 g / m ² , the surface density of the edge-mounted panels may be only a fraction, even reaching only about 25 g / m ² . It will be appreciated, however, that materials of significantly higher stiffness and / or density will be able to be used according to the present invention for acoustic panels with significant limitation or edge retention at least where there is no requirement for power at a lower frequency. Such use includes high-tone speakers, sirens, and ultrasonic speakers.

The use of material for panels with relatively low results in a higher coincidence frequency, a normal sound band that can improve by stiffness may, for example, over uniformity

: t ·· · channel sound from the speaker resonant panel. Such lower stiffness panels can provide an effective increase in mode density in lower registers and thus improve sound quality.

The illustrated useful variants for fully circumferential limitation or attachment of an edge or edge region include any lower extent of substantial limitation or attachment that the panel member or the active region of the substantially rectangular panel could form one side omitting what is shown for three sides, or two typically parallel sides, omitting what is shown for the other two sides.

The acoustic radiating members in this application are constructed in any manner suggested by the

WO97 / 09842, for example by means of at least one electromechanical excitation device. This excitation device may be adapted to the emitting member in any suitable geometrical already according to the principles or region of the acoustic member, as described in WO97 / 09842 impedance application, which is described in FIG. 1 may be omitted from the application of its own or each excitation in a position in which, according to analysis, mechanical application PCT / GB99 / 00404 or were experimentally. Such vibratory exciters for clarity.

As to the usable exciter type, reference can be made to WO97 / 09842, where such exciters can be positioned according to the principles explained in WO97 / 09842 and / or PCT / GB / 00404, usually with a difference acceptable for actual locations as compared to WO97 / 09842.

Useful investigations of resonant panel members with fully fixed edges, where these members form or are part of active acoustic devices, especially loudspeakers, are first shown in FIG. 11 to 16 of co-pending application PCT / GB99 / 00404 filed February 9, 1999, and these figures are repeated in this application as FIG. These studies are

Obviously based on analysis involving power transmission parameters, especially power fluency, specifically mechanical impedance, and mainly effects on the feasible to optimum. the location of the transducers and the shapes of the panel members, in particular the aspect ratios for the at least substantially rectangular panel members, and the location of the transducers on a proportional coordinate basis. Thus, the graphical representations of FIG. 6A, B, 7A, B and 8A, B for mechanical impedance with frequency for panel members of selected aspect ratios and isotropic in terms of bending stiffness are accompanied by a graphical representation of FIG. 9A, B, C for continuous mechanical impedance, as measured by the inverse mean standard deviation for positioning the appropriate positions of the respective transducers. Precisely calculated preferred aspect ratios of 1,160, 1,341 and 1,643 appear together with equally accurately calculated coordinates for the location of the transducers (0.437, 0.414), (0.385, 0.387) and (0.409, 0.439). In FIG. 10 is a diagram of calculated mechanical impedance for a quarter panel for an aspect ratio of 1.16, and shows a substantial range of areas suitable for positioning the transducer, even for two such discrete areas (dashed). In FIG. 11 shows a comparison of such preferred aspect ratios and the location of the transducer at the edge-mounted panel, also for aspect ratio 1.138.

Further investigations in this application, including substantially rectangular resonant panel members having increasing aspect ratios, are based on actual mechanical power measurements, and the resonant panel members in each case perform frequency response adaptation to a reference value or a straight line for the tenth above the lowest effective frequency. resonance modes. The contour diagrams of the inverse mean quadratic deviation of such a fit in the quarter panel are shown in FIG. 12A to H, including those that apply to the same or nearly the same aspect ratios as previously described (FIGS. 12A, B, D) and the corresponding FIGS. 13A to H for matching the frequency according to a straight line, wherein

The lighter coloring or shading represents the best feasible placement of the inverters and interruptions to the individual areas of the indicated feasibility at higher aspect ratios.

The expansion of these other researches with a aspect ratio as large as 1: 4 is remarkable, perhaps as a clear determination of feasibility at or near the square. This is unexpected, at least on the basis of our earlier discovery work and explanations regarding resonant panel members whose edges are substantially free for vibrations by bending wines. This also unexpected increase in operating power, as shown in FIG. 5A, B for 1.41 aspect ratio, is further made consistent with the other aspect ratios being investigated. Another unexpected significant reduction in the critical state of the aspect ratios to allow a uniform extension of the frequency of the resonant modes, which is advantageous for acoustic operation, provided a reason for further detailed consideration and analysis. The following conclusion is presented as a simplified beam theory for substantially rectangular resonant panel members having substantially isotropic bending stiffness.

In general, this implies confirmation of previous work and explanation that, essentially, for panel members with free edges, the lowest frequency of resonant modes, defined by the dimension of the next side, preferably in conjunction with the shorter side dimension corresponding to the next higher frequency of resonant modes, frequencies of resonant modes whose values are essentially interleaved. Indeed, due to the large aspect ratio for such a panel with essentially free edges, the second (possibly other) frequencies of the resonant modes of the panel members that can be directly attributed to the longer edge size would also be lower than the first frequencies that can be attributed to the shorter side dimension, would create a frequency gap that would be too large for faithful, satisfactory activity-based sound power

Bending wines at such respective lower frequencies.

In contrast, the first effective resonant mode frequency for a fully mounted resonant panel member effectively requires the benefit of the first resonant mode attributable to the shorter side length, ie the first combination of modes to operate the board vibration for two rows (fxi, fx ₂ : ... fx _n ) and (fyi, fy2: ··· fy _m ) for x, y axes parallel to the edges as expressed by the equation for the spectrum of resonance modes:

Up ' _m = V (A') ^{2 +} (^ ') ² n> 1 m> 1

The effect of this quadratic relationship is that a large aspect ratio can create an order of quite closely spaced resonant mode frequencies that can be attributed to the benefit of the next higher order belonging to the longer edges before the next benefit of the next higher order belonging to the longer edges. In FIG. 14 is a diagram showing the maximum inverse of the mean quadratic power deviation versus aspect ratio, and an increase in power fluency (above the lowest effective resonance modes) with an increasing aspect ratio of up to about 1: 3 is shown. Indeed, the larger aspect ratios for the marginally constrained members have tighter resonant mode frequencies, while the opposite fits with relatively free edge panels according to WO97 / 09842.

However, this result does not in any way deviate from good and usable results for acoustic devices that use smaller aspect ratios with fully fixed edge panels and is also quite practical for the desired operation of the device with an overlapping frequency of resonant modes as outlined above. the above analysis as well as PCT / BG99 / 00404.

However, there are significantly greater design possibilities. In any particular case and desired use for acoustic devices, individual resonant mode frequency spectra will likely vary with aspect ratio for given bending stiffnesses and ratios, and often can be selected based on calculated, non-measurable or understandable results according to desired or acceptable performance (characteristics) of acoustic equipment.

Furthermore, another relevant factor has been identified and investigated, namely acoustic performance and sound power related to an axis or position where there may be significant differences, and these may be appropriate or effective in the design of individual acoustic devices for a particular use, in particular differences may be positively desired or may be undesirable, or in individual preferred or acceptable combinations. In FIG. Figs. 15A-15J show combined polar diagrams for one resonant panel member with a 1: 3 aspect ratio, for lower resonant mode frequencies, and in each case one area is shown in solid line and the other area is dashed, i. with a larger horizontal or respectively vertical dimension. As generally expected, radiation patterns are significantly different, so that they are usually smoother in a plane of shorter length and more diffuse in a plane of longer length. The design option includes the acceptance of a higher frequency of the lowest resonant modes that directly depend on aspect ratios for any single panel member design; furthermore, acceptability of directivity where the vibration of the panel member is significantly different in different axial directions; logically resulting in different power fluctuations in the respective radiation planes; associated selection of the orientation or position of the panel member used as usual; and available trade-offs between power flow in different planes and / or total power flow depending on the similarity or otherwise of the responses of the first and second planes or the azimuth and elevation planes.

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The panel member of FIG. 16A contains a black glass coating of 0.05 mm thickness on an aluminum structure of 4 mm thickness, resulting in a substantially isotropic bending stiffness of 12.26 Nm, a basis weight of 0.76 kg / m ^2, and a coincidence frequency of 4.6 kHz. The panel member of FIG. 16B contains a black glass coating with a thickness of 0.102 mm on a 1.8 mm thick Rohacell core resulting in a substantially isotropic bending stiffness of 2.47 Nm, a basis weight of 0.60 kg / m ² and a coincidence frequency of 9.1 kHz . The panel member of FIG. 16C contains a 0.05 mm Melinex ™ -us coating on a 1.5 mm Rohacellu core resulting in a substantially isotropic bending stiffness of 0.32 Nm, a basis weight of 0.35 kg / m ^2, and a coincidence frequency 19.2 kHz. All these panel members have a similar aspect ratio from 1.13 to 1.14 and are driven by the same drivers with an active diameter of 13mm and an input impedance of 8 ohms. For each panel member, the sound power was measured with all panel edges that were free with respect to panel vibration due to the bending of the wine, and all panel edges that were fastened against such vibrations. In FIG. Figs. 16A-C show that the fastening results in a substantial increase in the acoustic power below, but not above, the coincidence frequency, so that the advantageous effect of the fastening is greater the higher the coincidence frequency and the lower the bending stiffness of the panel member concerned.

The panel members of FIG. 16D and 16E have the same stiffness structure as the members of FIG. 16A, but have larger dimensions, 360 mm x 315 mm, respectively. 545 mm x 480 mm, compared to the dimensions 260 mm x 230 mm of FIG. 16A to 16D; thus, it has been confirmed that full mounting creates improved acoustic power from the coincidence frequency down to the lowest resonant mode frequency of the respective panel member, in particular up to about 400 Hz for the smallest panel members (as shown in Figs. 16A-C) and lower for larger and larger. largest panel members. It is also important to note that the larger the panel members, the closer the mode shapes are for the · · pre · · · pre pre · · · · · · · · · · The frequency is approximately equal to the sine wave.

For all these panel members, a control measurement of the mechanical power was performed, in their excitation with the edges free for vibration and with the edges fully fixed, and it was shown that all of these panel members received mostly the same power.

Regarding that useful acoustic radiation is not feasible below the coincidence frequency, it may be interesting to consider, in contrast to the explanations given in WO97 / 09842, the assumption based on the theory that such radiation can be expected from perfect sine waves in an endless plate; and assumptions logically related to the explanation of WO97 / 09842, clearly stating that useful acoustic radiation is feasible in the final plate below the coincidence frequency, that such radiation results from portions of the final plate that vibrate with a deviation from the perfect sinusoidal distribution, it seems to be mainly the case for the lowest frequency modes, both near the excited exciter, and also at the edges that freely vibrate, so of course the focus is on the latter. However, according to the explanations of the present application, it is now clear that the limiting of the edges, especially as regards the vibration capability of the bending wines, has a beneficial effect on the acoustic connection to air, in particular to increase their efficiency below the coincidence frequency. Of course, this occurs in the context of the acoustic power necessarily associated with losses in the resonant panel member and in the acoustically near field, where at least the latter is clearly reduced by its marginal limitation which effectively eliminates the acoustic short circuit around such edge (s) exposed to such limitation.

It seems logical to explain the increased acoustic connection to air below the coincidence frequency with reflection of such energy that would otherwise be lost in an acoustically close field solely on the basis that such energy is in the vibration of the bending wines. Frequency of resonant modes of the panel member within the appropriate acoustic range, and must leave the panel member as acoustic energy, whether as an improved air connection in limited regions or in the middle of a panel member. The situation above the coincidence frequency is, of course, unaffected. Of course, this is all in a further context with the available resonant modes of the edge-limiting panel members, which is of course necessary without twisting the vibration modes that are effectively reduced or eliminated by the edge-limiting, especially fastening.

Further investigations have been carried out on the advantageous positioning of the second transducer, based on the measured effect, using a displaceable or displaceable second transducer; and to limit or fix the individual edges using inertia masses in localized positions. The result, as far as the location of the second transducer is concerned, mainly emphasizes the extent and complexity of the interaction between the effects in the resonant panel member of the two transducers. Indeed, the best established positions for the second transducer relative to the preferably located first transducer for the resonant panel member, substantially rectangular in shape and substantially with isotropic bending stiffness, were in fact center and near center and three quarters or near three quarters of length along the axes defining the quarter of the panel in which the first transducer was located, and the acoustic output quality tended to be adversely affected (although feasible for some applications). The result for individual constraints or mountings was particularly interesting in that it exhibited a potentially advantageous transition from close equivalence to continuous constraint or attachment for the effect of the acoustic frequency pass filter related to greater distances and the relationship (s) to the wavelengths of the bending wines in the respective panel. member.

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Claims (26)

An acoustic device based on the activity of bending wines and capable of operating below the coincidence frequency, comprising a member providing acoustic operation for the advantageous distribution of resonant modes by the action of bending wines in said member, characterized in that it comprises means at least partially delimiting said member wherein the means has substantially limiting properties with respect to the vibration of the member by means of bending wines, wherein the bounding means is arranged in the peripheral edge of the member and is arranged circumferentially over at least 25% of said edge. 2. An active acoustic device comprising a bending wine member having a preferential distribution of resonant modes therein, and a preferred bending wine converter, comprising a means at least partially delimiting said member, said member having substantially restrictive properties with respect to the vibration of the member by the bending wines, and the location of the bending wine converter is defined in relation to and with respect to the bounding means, the bounding means being arranged in the peripheral edge of said member and circumferentially arranged over at least 25% of said edge. Acoustic device according to claim 1 or 2, characterized in that the limiting means is at least partially critical for said acoustically active region, said member being part of a larger structure. Acoustic device according to any one of claims 1 to 3, characterized in that the limiting means is arranged along one side of a substantially rectangular area or panel member. Acoustic device according to claim 4, characterized in that the boundary means is also arranged along the opposite parallel side of said region or panel member. Acoustic device according to any one of claims 1 to 5, characterized in that the bounding means is arranged completely around said region or edge. Acoustic device according to any one of claims 1 to 6, characterized in that the limiting means contributes significantly to the overall stiffness of the member for its efficiency in the desired acoustic operation. Acoustic device according to claim 7, characterized in that the bending stiffness of the member in the acoustically active region is below about 5 Nm. The acoustic device of claim 8, wherein said bending stiffness is above about 0.001 Nm. Acoustic device according to claim 7, 8 or 9, characterized in that the surface density of the member in the acoustically active region is from about 25 g / m ² . Acoustic device according to any one of claims 1 to 10, characterized in that said region of said member has an isotropic bending stiffness. Acoustic device according to any one of claims 1 to 10, characterized in that said region of these members has bidirectional anisotropic bending stiffness. ···························· Acoustic device according to any one of claims 1 to 10, characterized in that said region of said member has a bending stiffness distribution corresponding to the desired preferred location of the transducer. Acoustic device according to any one of claims 1 to 13, characterized in that said region is substantially rectangular and has an isotropic bending stiffness and has an aspect ratio of 1: 1 to 1: 1.5. Acoustic device according to any one of claims 1 to 13, characterized in that said region is substantially rectangular and has an isotropic bending stiffness and has an aspect ratio greater than 1: 1.5. An acoustic device according to claim 15, wherein said aspect ratio is about 1: 3 or greater. Acoustic device according to any one of claims 1 to 16, characterized in that said limiting means serves at least to limit the resonant modes of operation of the bending wines allowing twisting. Acoustic device according to any one of claims 1 to 17, characterized in that said limiting means serves at least to limit the disturbance of the near field acoustic output. Acoustic device according to any one of claims 1 to 18, characterized in that said limiting means serves at least to increase the acoustic output from the energy of the resonant action of the bending wines in said region. An acoustic device according to any one of claims 1 to 19, wherein said member is tensioned. ························ Acoustic device according to claim 20, characterized in that the member is tensioned in two transverse directions. An acoustic device according to claim 21, characterized in that the tension in the two directions is the same. Acoustic device according to any one of claims 20 to 22, characterized in that the bending stiffness of the member in the acoustically active region is low. An acoustic device according to any one of claims 20 to 23, characterized in that the surface density of the member in the acoustically active region is low. Acoustic device according to any one of claims 1 to 24, characterized in that the boundary means forms an integral part with said member. 26. An acoustic device according to claim 25, wherein the boundary means forms an integrally cast portion with said member.