MXPA01005340A - Acoustic devices - Google Patents

Abstract

A method of reducing features occurring at particular frequencies such as at coincidence is described. A panel (11) has exciters (13, 15) arranged to reduce the feature. The exciters may be driven in phase but be spaced apart by a distance substantially equal to half the wavelength of bending waves in the panel at this particular frequency.

Description

ACOUSTIC DEVICES DESCRIPTION FIELD OF THE INVENTION This invention relates to acoustic devices that include a panel-shaped member which, for acoustic operation, depends on the action of the bending wave, with a distribution of resonant modes of surface vibration and which have arisen. specifically in relation to loudspeakers or speakers in the form of a panel.

BACKGROUND OF THE INVENTION According to what is stated in the various patent applications of the New Transducers Limited itself, starting with the published International Application WO97 / 09842, loudspeakers or loudspeakers, in the form of a panel, are susceptible to optimization as far as possible. to the characteristics of geometry and flexural stiffness of the panels involved and to the location of the excitation exciters? of these panels and for them. Even if already optimized, circumstances may arise in donp ^ e, during the operation, some frequencies are candidates for the variation of their contributions, for example, untimely in a certain way, so that the reduction, even the practical suppression, would be useful. of your contributions. Of course, a particular example has to do with coincident frequencies that, at least in large panels, result in directional radiation at extreme angles towards the panel surface and produce irregularities beyond the smoothing effects, dimensionally related and inherently useful in smaller panels.

SUMMARY OF THE INVENTION In accordance with a first aspect of the invention, there is provided a bending wave horn comprising: a panel capable of supporting bending waves; a first exciter mounted on the panel to excite the bending waves in the panels and produce an acoustic output, wherein the response to the acoustic output of the panel excited by the first exciter has a particularity at a known frequency; and a second exciter mounted on the panel to excite the bending waves in the panel and produce an acoustic output, wherein the second exciter is arranged or arranged so that when the first and second exciters are excited together, the particularity. The second exciter may be placed at a predetermined distance from the first exciter to soften the particularity. The relative phase and the gain of the first and second exciters can be controlled; the second exciter may have a filter, attenuator, delay, phase control, signal processing and / or variable gain control i associated therewith. Since, in general, what matters is the relative amplitude and phase of the signals supplied to the two exciters, alternatively or additionally a filter, attenuator, delay, phase control, signal processing or associated variable gain control can be provided to the first exciter. The second exciter may be connected in phase or in opposition to the first exciter. A combination of any or all of these methods may be used. The particularity may be a peak, a prominence or elevation in the acoustic output (sound pressure level) as a function of the frequency for a constant excitation voltage. The horn, according to the invention can; in accordance with this, to have an improvement in the frequency response in which the particularity is softened. Preferably, the second exciter is disposed separately from the first exciter in the panel at a distance substantially equal to half the wavelength of the bending waves in the panel at the known frequency. It may also be possible to use odd multiples of half wavelength, that is, one and a half times the wavelength, two and a half times, etc. The first and second exciters are preferably connected in phase between common terminals. This is easily done by connecting the same exciters in the same way and around; in a series or parallel arrangement; the bending waves1 can then be emitted in phase. Of course, when the exciters are separated by half a wavelength at a particular frequency, the phase relationship at that frequency will cause the desired degree of cancellation to provide control and / or smoothing. If the second exciter were simply to be excited in counter phase with respect to the first exciter without considering the placement of the second exciter, then the first and second exciters would tend to produce destructive interference over a wide range of frequencies, resulting in a low output, especially at low frequencies. frequencies. In contrast, by placing the first and second exciters at a distance of half a separation wavelength, the first and second exciters can be excited in phase to increase the acoustic output. Only at the known frequency will the bending waves excited by the two exciters be in contraphase and, hence, will be canceled. In accordance with the foregoing, the horn i according to the invention can have an improved response at the particular known frequency. Preferably, the known frequency is the coincidence frequency. At the coincidence frequency, the acoustic properties of the panel change in a non-smoothed manner. Accordingly, there is often a peak or rise in the acoustic response to this frequency. This can be smoothed in the horn, in accordance with the invention. The panel can be anisotropic and have different coincidence frequencies associated with the first and second axes. The second exciter may be separated from the first exciter, along the first axis, to smooth out the particularity of the coincident frequency associated with the bending waves, along the first axis, and a third exciter separated from the first exciter may be provided, along the second axis, at a distance practically equal to half the wavelength of the bending waves at the coincident frequency associated with the second axis. A fourth exciter may be provided; The first, second, third and fourth exciters can define a rectangle on the surface of the panel. Additional exciters may be added as required, for example, to provide sufficient output power. The exciters can be separate transducers. For example, each exciter may comprise a moving coil fixed to the panel and a magnet unit arranged or arranged for relative movement with the moving coil. The exciter may be inertial, that is, the magnet unit need not be fixed in a separate frame, although the force on the panel may react against the inertia of the magnet unit. If the exciters are excited in phase, some of the parts may be common. For example, the first and second exciters may comprise a single transducer that has a coil and a magnet unit, the coil has a first region that contacts the panel (the first exciter) and a second region that makes contact with the panel (the second exciter), the two positions are separated by half the wavelength of the bending waves at the known frequency. Although it is preferred to separate the exciters at particular distances, this is not always possible. Accordingly, in the alternative embodiments, the second exciter may be located near the first exciter and excited in push-pull. In this case, a bandpass filter can be used, so that the second exciter is only excited in a predetermined frequency range around the known frequency. In the embodiments, a small number of exciters can be arranged to operate at high frequencies well above the coincident one, for example, to reduce the effects of interference at these frequencies. This can be done by arranging or arranging filters associated with the exciters already described, so that only one of them operates at higher frequencies. Since this may alter the electrical and mechanical symmetry of the first, second, third, etc. exciters, one or more additional and separate high frequency drivers may be provided as an alternative. The provision of a single higher frequency driver may be advantageous for reducing the effects of acoustic interference at higher frequencies. When one or more separate higher frequency exciters are provided, the low and high frequencies present in an excitation signal may be separated by one or more splitter circuits to feed the higher frequency driver with frequencies above the cutoff point and to feed to the other exciters with the frequencies below the cut-off point. The detailed design of the dividers is well known in the technique of horns; The divisor can be as defined as required. The divider should not be confused with the aforementioned bandpass filter, although the circuitry for each can be combined if convenient. According to a second aspect of the invention, a bending wave horn is provided, comprising: a panel capable of supporting bending waves, first and second exciters mounted on the panel to excite the bending waves in the panel and produce an acoustic output, wherein: the first and second exciters are separated by a distance of half a wavelength at a predetermined frequency, so that when the first and second exciters are excited together, the acoustic output of the panel to the default frequency. The first and second exciters may be connected in push-pull to increase the acoustic output at the predetermined frequency or in phase to soften or reduce the acoustic output at that frequency. An improved response at a particular frequency is particularly useful for sirens and other acoustic warning devices, where only output to known frequencies is required.

For the most normal requirement of a smooth response from the horn, the first and second exciters may be connected in phase. In this case, other features described above may also be used < with reference to the first aspect of the invention, if appropriate. According to a third aspect of the invention, there is provided a method for suppressing a particularity in a frequency response of a bending wave horn having a panel (11) capable of supporting bending waves and a first exciter (13) mounted on the panel, including determining a frequency at which the response i of the first exciter of the panel has a particularity, providing on the panel a second exciter (15) arranged so that when the first and second exciters (13, 15) be excited together, the particularity softens. The second exciter may be provided in the panel at half the wavelength of the bending waves of the panel at the known frequency. The step of determining the frequency can determine the coincidence frequency associated with a predetermined address. According to a further aspect of this invention, a panel-shaped horn that depends on the action of the bending wave with the beneficial distribution of the resonant modes of vibration has the control of at least one frequency, in accordance with the separation between at least two exciter means as they are associated with the panel involved. The separation can be from an exciter means in a location optimized for the excitation of the panel to another additional exciter means and can be directly related to the transmission speed of the bending waves in the panel for the frequency, which corresponds specifically to half length of wave for the reduction until the satisfactory suppression, when both excitatory means receive the same signal in phase. It is feasible to supply practically only one frequency to the additional exciter means, say by narrow bandpass filtering, and subjecting it to the delay that allows the separation to be other than half a wavelength, although with practically the same effect. Another adjustment capability is available from the delay applied to the rest of the input signal, albeit desirably, not differentially, as supplied to the multitude of driver means, usually in optimized locations. It is the case that, by supplying the second additional exciter means to a half-wave separation in push-pull, with respect to the exciter means, the opposite effect will be had, that is, an increase in the contribution of the frequency in the acoustic output of the speaker in the form of a panel. The direction of separation is also significant. In this way, and as another inventive aspect thereof, bending waves in a particular direction of separation between two exciter means are affected at a frequency corresponding to said separation. Two of these frequencies can be adequately affected by different separations in the same direction, usually on each side of the exciter means in an optimized location or in different directions for frequencies associated with these different directions, In special embodiments of this invention and for the frequency related to a length or width of a practically rectangular panel, the separation will be in correspondence with the direction, ie, parallel: to one of the longitudinal or wide sides or axes. Of course, it is practical to handle at least one of each of the frequencies related to the length and width of this rectangular horn panel, either by means of the additional exciter means, specifically separated with respect to the optimized location of an exciter means, or else each with respect to a different optimized location! of the exciter means When different optimized locations are used for the exciter means, it may be convenient to treat each one differently) as to the association of the separate additional exciter means for the purposes of the present, including the non-association of that type with one or more of these optimized locations used, even if it is not typical; the association using an address of the same separation, thus the frequency involved from only one up to all the optimized exciter locations used; the association using another opposite separation in the direction (in this way, another related frequency), for at least one of the last used locations of the optimized exciter; the association using another direction and the separation (in this way, another frequency involved), with at least one of the exciter locations optimized and used, also has the association with a direction and separation; the additional association with the additional exciter means in different directions and separations of the same optimized location of the additional exciter means, in significant separations for the purposes of the present. At least for frequencies filtered in a bandpass filter and that will be affected, of course it is feasible to use other separations and delays selectively applied to obtain practically the same effects, even | a standardized separation and different delays. At least where the embodiments of the present are applied for more than one frequency involved, jointly with respect to an optimized location of the exciter means, it may be useful to apply the step filtering to the input signals, so that only A selected band is applied to all the excitatory means and associated to that optimized location. The embodiments of this invention that provide reduction to suppression based on a selective frequency are considered with a particularly useful application to obtain an improved acoustic performance with respect to the aforementioned particular problems, which have to do with the coincident frequencies, according to it will be described and illustrated in a specific way. It is noted that the embodiments of this invention that provide reinforcement based on a selective frequency, have a particularly useful application, where a warning siren and / or greater loudness or neutralization of messages are required, etc. (hence the feasibility with the operation relative to a band of selected frequencies). Where the components of the signal that will be affected have directionality in the output from the horn panels, the embodiments of this invention can be displayed in connection with the desired directionality effects, which include the reduction or emphasis thereof. In the implementations of this invention at least for the reduction / suppression of a selective frequency and the involvement of the separate exciters operating in phase, a certain degree of equivalence is observed with a greater excitation of area, hence the possible use of excitatory means effective or actually greater area, and then the compensation of unavoidable effects in the band of available frequencies by means of excitatory means of smaller area in other locations, together with some filtering of appropriate step.

BRIEF DESCRIPTION OF THE DRAWINGS The specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a horn according to the invention; Figure 2 is a plan view of a first embodiment of the invention; Figure 3 is a side view of the first embodiment; Figure 4 is a graph of the acoustic power output at 80 ° with the axis perpendicular to the horizontal, using two separate exciters in the horizontal direction and for comparison, using a single exciter; Figure 5 is a graph of the acoustic power output at 80 ° with the axis perpendicular to the vertical axis, using separate exciters in the vertical direction and for comparison, using excitators not so separated; ^ Figure 6 shows a divisor array of the first mode; Figure 7 shows an alternative divisor array; Figure 8 shows a second embodiment having nine exciters; Figure 9 shows the splitter array in the second mode; Figure 10 shows the electrical impedance of the second mode; Figure 11 shows the simulated panel offset of a one-dimensional sample using two exciters; Figure 12 shows the simulated panel displacement of the sample of Figure 11 energized only with a driver; Figure 13 shows the pressure response in the example of the arrangement of figure 11; Figure 14 shows the sound pressure as a function of the angle at 541.7 Hz; Figure 15 shows the sound pressure as a function of the angle at 2039 Hz; Figure 16 shows the sound pressure as a function of the angle at 4515 Hz; Figure 17 shows the integrated sound pressure at all angles; Figure 18 shows a plan view of a horn according to the invention; Figure 19 shows a side view of the horn shown in Figure 18; Figure 20 shows the measured results of the panel of figures 18 and 19 that excite a driver; Figure 21 shows the measured results of the panel of figures 18 and 19 which excites two exciters y; Figure 22 illustrates an additional arrangement.

DETAILED DESCRIPTION INCLUDING ILLUSTRATED MODALITIES. Referring to the following equations (Equation 1 and Equation 2), the speed dependence of the wave (v) across a frequency panel surface (Equation 1) results in a coincident frequency (Equation 2) to which it is Wave velocity is equal to that of the velocity1 of the sound of the panel without losses. At this coincident frequency, a polar plot of the large panel, for example, 1450 mm by 1100 mm, will show the peaks in sound pressure level (SPL) that occur at extreme angles to the panel surface. This is more evident in larger panels for several reasons. The optimal bending stiffness (B) is greater in larger areas, so the coincidence frequency is lower. Any "CONCENTRATION" effects of smaller panels are scattered due to a busbar or distortion function related to the dimensions of the panel. Also, the larger panels experience a reduced distortion effect, hence the peaks become more evident.

Equation 1 Where v (t, ß, μ) is the speed of the wave, which depends on f, the frequency in Hz, of ß, the flexural rigidity of the panel material, with units in Newton-meters and μ, the density of area, in kilograms per square meter.

Equation 2 fc (ß, μ, v) = 2pÍß Figure 1 shows a schematic diagram of a horn according to the invention. A panel 11 has first and second exciters, 13 and 15, mounted on its surface. The measurements are taken by moving a microphone 17 along a horizontal path 19 to measure the response of the acoustic power as a function of the angle from the center line 21 perpendicular to this panel. The first exciter 13, is arranged in an optimal excitation location for coupling to resonant bending waves in the panel, as taught in other patents and applications on behalf of New Exciters Limited, such as O97 / 09842. The second exciter is separated from the first in order that the response at the extreme angles and that associated with the matching frequencies is smoother. For this purpose, the center-to-center spacing S of the exciters 13 and 15 is half the wavelength of the coincident frequency of the waves along the horizontal axis 35. Figures 2 and 3 show a specific embodiment of the idea A rectangular anisotropic panel 11 measuring 1450 mm by 1100 mm has a core 10 mm thick and films or covers 27 0.106 mm thick epoxy resin loaded with carbon fibers. The covers are attached to the core with an epoxy resin film 29 of 90 gsm. (grams per square meter) loaded on a cotton carrier I. Mounts 23 are provided to support the panel during use. In order for the panel to function as a projection screen, the PVC 31 projection material of 534 gsm was added to the panel with 3-sided double-sided film. The panel had a bending stiffness B of 184 Nm along the first long axis 35 of 71 N along the second short axis 37 and a bulk density per unit area of 1.92 Kg / m2. The coincidence frequency is the frequency at which the wave velocity in the panel coincides with the speed of the wave in the air, considered as 344m / s. Using the above parameters and equation 1, the coincidence frequency1 associated with the waves in the x direction can be calculated in 1924Hz. Half of the wavelength of this frequency is 89.583mm so that the second ter 15 is mounted 90mm from the first 13 along the longitudinal axis. Although the calculation is effectively related to point source ters, the typical ters available can be up to approximately 25mm or more in diameter. This is not necessarily a point source and some optimization settings may be necessary, although they can easily be found by trial and error. The maximum tolerance in the position is in the range of 5 to 10%, it is expected to apply for example, approximately 5mm. In the coincidence frequency and just above it, that is, approximately 2KHz, the sound is emitted at that frequency with an intense maximum at an angle of 80 degrees with respect to the center line 21. Figure 4 shows the output to 80 ° both with compensation and without compensation using the second ter. The measurements were made at a distance of 2m using the tation of IV, with and without the second ter 15. The upper line in Figure 4, which shows the peak at around 2kHz, shows the tation output using only the first ter. The improvement using both ters 13 and 15, is readily apparent in Figure 4 and can be seen in the lower line measured using the tation of both ters. This line does not show the peak of coincidence. Using the two ters 13 and 15 only the particularity with respect to the concentration in the horizontal plane (the x-axis 35) is corrected. However, the concentration can also occur on the y-axis. Since the panel is anisotropic, the coincidence frequency and the wavelength of the waves along the y-axis is different. The separation of half wavelength in the coincidence is calculated as 54 mm, in the same way as before. Accordingly, I the third and fourth ters 17 and 19 are provided with a 54mm spacing of the first and second ters, 13 and 15, along I of the y axis. The four ters form a rectangle. The reason for using the rectangle is that it preserves physical symmetry. This in turn makes the mechanical impedance of the ters practically the same and in this way, the group is easier to te. The results showing the improvement using the pair of additional ters are presented in Figure 5. The thinnest line with a peak at 3kHz represents the acoustic output at 80 ° below the horizontal, using only the first pair of ters and the thick line shows the effect of using the four ters. As before, the peak in coincidence is significantly reduced. There is very little coincidence effect on the axis, that is, measured by a microphone along the center line, under anechoic conditions. However, when the speaker is installed in a room with echo, the listener can hear the sound output at all angles, which can reach the listener after being reflected by the walls. The horn, according to the invention, provides an improved response, even on the axis, in these real conditions. A higher frequency driver 21 (FIG. 2) is provided to operate only at high frequencies. The lower and middle frequencies, including the coincidence frequency, are produced by the first to fourth exciters, 13, 15, 17, 19 This division of the frequency range can reduce the undesirable effects of high frequency interference caused by multiple excitation exciters. The exciters are preferably excited by a divider circuit 20 as shown in Figure 6. The first to fourth exciters are connected between shared common terminals, namely, an excitation input point 22 and the ground 24. The terminals may be connected to a signal source, such as an amplifier. The higher frequency driver 21 is connected in parallel to an inductor L3 and both are connected in series with a C3 capacitor; it can be excited from common terminals or from separate terminals. The first to fourth exciters 13, 15, 17, 19 are excited together, divided into two parallel pairs in series. This arrangement or arrangement of exciters is connected in s, erie with an inductor L2, a resistor R1 and a capacitor C2 in parallel, which provides a weak filter to provide additional control of the frequency response. In turn, this weak filter is connected to the input 22 through an inductor Ll and to the earth 24 through a capacitor Cl, to provide the low pass action. The components shown have the following values: Ll 0.92mH (low resistance), L2 5.0mH, 0.4O, L3 0.9mH (low resistance), Cl 6.8μF, C2 lOOμF, C3 6.8 μF and Rl 30O. An alternative arrangement to excite the four exciters 13, 15, 17, 19 is presented in Figure 7. In this arrangement, two of the first to fourth exciters are bridged by a capacitor 39 which short-circuits the high frequencies . In this way, only two exciters are excited at higher frequencies. Figure 8 shows a variant of the previous embodiment having additional exciters. The first to fourth exciters are the same as in the previous mode. In this complete system the fifth 41 and the sixth 43 exciters are provided in good locations for coupling with the resonant lexion waves in the panel. The seventh 45 and eighth exciters 47 are respectively associated with the fifth and sixth exciters, separated from them along the horizontal axis 35. This is because the irregularities due to the directionality in the horizontal plane are of a much greater significance for listeners that vertical irregularities and, these irregularities can be corrected by horizontal separation. A ninth exciter 49 is also located separately from the fifth exciter in the opposite direction to the seventh exciter with a different spacing along the first axis. The divisor system associated with the complete system of nine exciters is shown in Figure 9. Its calculated or simulated electrical impedance is shown in Figure 10. The resistance falls to a minimum of 8 ohms approximately between 12KHz and 500Hz; this is particularly friendly to the input signal amplifiers and will easily provide the vision for connecting other systems in parallel with the horn panel 30, if desired, and reduces the chances of overloading the amplifier. The provision of the divider actually allows only the fifth exciter to be active for the high frequency acoustic output radiation and is an effective extension of other improvements to the response to high frequency. The complete system of nine exciters of Figure 3 has a beneficial optimization effect in terms of the angularity in the behavior of the acoustic output and the extension of the operation at low frequency. The measured echoic response is shown graphically in Figure 8 based on the axis along with a base-end angle of 80 degrees. I The multiple exciters as used herein offer greater control over directionality and increase the maximum SPL levels and bandwidth. This control is achieved by deactivating effectively or by causing; the destructive superposition in relation to the selected bending waves in a panel, the region of affected frequency that will be controlled by the specific locations of the exciters in the 1 panel area and that easily include any coincident frequencies or frequencies are applied with the Removal achieved of approximately an IOB SPL that otherwise occurs at extreme angles with respect to the panel surface. The typical large-sized speakers, indicated in Figures 1 and 2, often serve as center channel speakers, perhaps also the display screens for so-called home theater or multimedia installations. Typically the frame specifications that allow the connection of the panel 11 to a wall by the mounts 23 and may also allow the connection of a cosmetic edge to the front of the panel 11. The performance at low frequencies can be improved by a minimum separation of the panel fromFor example, any back wall can be achieved by attaching a layer of acoustically absorbent material, for example, a sheet of polyurethane foam to the back of the panel and its normal frame, say to provide an absorption above 800Hz and a Rear spacing of approximately 40 mm to 80 mm All dimensions marked in Figures 1, 2 and 8 should not be treated in more than completely exemplary fashion. Some exciters, marked with a cross in Figure 8, are located in optimized locations, in accordance with the scope in distributed mode, see, for example, O97 / 09842. A configuration of four exciters can be used where all the exciters are operating on the basis of a full range in a series-parallel combination, say to produce a 6 ohm load on a signal supply amplifier. Alternatively, the frequencies of the input signal above the region for cancellation of the effects related to the matching frequencies could be radiated from the exciters 13 and 15 by connecting a high pass filter through the other exciters, see Figure 7 and the capacitor 39. This can produce a higher frequency rise (if required or desired and variable by means of a suitable resistor in series with the capacitor 39) and reduce the effects of interference at high frequencies that can be audible by a listener who walks around the panel. To maintain symmetry as mentioned above, among cancellation excitators regarding the mechanical action in the cancellation range, the phases of the currents flowing in each of the exciters should change as little as possible and any necessary compensation should be applied , for example, a 6μF capacitor will result in a 12-degree shift of the current phase to 2KHz and can be equated to a 3mm reduction in the separation, which can be compensated for by a similar increase in the separation between the pairs of exciters 13 and 15 and 17 and 19 in Figure 2 or 8. The use of a resistor in series with the capacitor 55 can reduce the shift compensation of the separation. Additional exciters have little effect on the anechoic frequency response on the shaft, since most of the panel does not fall on the lines that connect the exciters. Most of the surface of the panel is therefore subjected to the behavior of the normal bending wave, caused by the positions of the standard exciters. The measurement of the echoic response (in the room) shows an improvement when the method is used, as does the reflection of the walls, ceiling and floor that have an additive smoothing effect. Figures 11 and 12 are related to the calculations of the displacement of the panel. When a bending wave panel vibrates, the displacement of the panel related to the action of the bending wave occurs. Instead of a simple forward and backward movement of the entire panel, as with conventional piston speakers, more complex patterns of displacement are presented. Figure 11 shows the calculation of the displacement of the panel, using two exciters separated in 71 and 73 and Figure 12 shows as a comparison the displacement of the panel using only one exciter in 71. Both figures are related to the calculations that use the energy supplied by the exciters at the coincidence frequency. These two figures are simplified, since the panel is modeled in a longitudinal dimension and in a perpendicular dimension. In accordance with this, part of the complexity of the real two-dimensional panels that flex to cause displacement in the third dimension is lost. However, the results show that the displacement of the large panel to the coincidence observed in Figure 12 uses only one exciter that is practically canceled in the arrangement of Figure 11 with two exciters. In the acoustic domain, this effect results in the reduction of the sound pressure level at extreme angles to the panel surface at the coincidence frequency. This is because the displacement of the large panel is coupled to the air to produce sound at extreme angles and this coincidence effect (often known as concentration) is reduced. For the cases of one and two exciters, from Figures 11 and 12 the sound pressure on the axis has been calculated and the results are shown in Figure 13. The results for an exciter are shown in the lower solid line and the results for two exciters are shown on the upper dotted line. Since two exciters produce twice as much power, the dotted line is at a sound pressure level generally three decibels above that of the solid line. The results are calculated for the anechoic case, that is, they did not take into account any echo. No peak is visible in the response to the pressure of the frequency function, with any one or with two exciters; this is because the peak in the coincidence emits sounds at extreme angles to the axis. Therefore, to show the effect of using two exciters, it is necessary to consider the angular dependence of the sound pressure level. Figure 14 shows the sound pressure level radiated in different directions at a frequency practically below the coincident at 541.7 Hz. As can be seen, radiation is practically isotropic at this frequency. Figure 15 shows the result to the coincidence (2039 Hz). The results of a single exciter show peaks and depressions, very important at extreme angles. These peaks and depressions are significantly softened in the case of two exciters. Figure 16 shows results well above the coincidence at 4515 Hz. On this frequency cancellation does not occur. An alternative way to present these results is to integrate the entire sound pressure level at all angles as a function of frequency. Figure 17 shows the result, again with one and with two exciters. The peak at coincidence (around 2000 Hz) is significantly larger with an exciter than with two exciters. These calculated results have been confirmed using measured samples. The test sample is shown in Figures 18 and 19 and is constituted by an aluminum honeycomb 51 of 3.5 mm in thickness with films or liners 53 of carbon fiber and a vinyl cover 55 adhered to the front face with a thermoplastic gauze. 50gsm. The panel is a rectangular panel measuring 220mm along the short axis 57 by 440mm along the long axis 59. The first and second exciters 61i and 63 are mounted on the panel; Each of these is a 25mm exciter with a ring of reduced mass that I attaches to the panel. The first exciter 61 is located at 94mm along the short axis and 195mm along the long axis, measured from the nearest corner; the second exciter 63 is mounted 43mm from the first exciter at an angle of 22.5 ° to the nearest corner from the direction of the first long axis. Figure 20 shows the acoustic power measurements with this panel energized with the first exciter 61 and Figure 21 shows; the results of the excitation of both exciters, 61 and 63. It should be noted that in these two Figures, the data below 200 Hz should be ignored, since they were not captured accurately by the measuring equipment. From the comparison of these graphs, it can be observed that the peak at the coincidence frequency (around 3600 Hz) was significantly reduced using two exciters instead of one. Unlike the larger example of Figures 2 and 8, this panel is sufficiently small in the direction along the short axis (220mm) that the concentration in coincidence in the direction of this axis is not a significant problem. In accordance with this, good results can be obtained using only two exciters. Figure 22 shows a detail of an alternative arrangement in which the first 13 and second exciters 15 are arranged in close proximity and the second exciters are connected in opposition to the first exciter by means of a bandpass circuit 81 and the conductors 83. As mentioned above, this arrangement can be used with other separations between the different exciters at half wavelength of the particularity.

Claims (26)

1. CLAIMS; A bending wave horn comprising: a panel (11) capable of supporting bending waves, a first exciter (13) mounted on the panel to excite the bending waves in the panels and produce an acoustic output, where the response to the acoustic output of the panel (11) excited by the first exciter (13) has a particularity at a known frequency, and a second exciter (15) mounted on the panel to excite the bending waves in the panel (11) and producing an acoustic output, characterized in that: the position, the separation, the orientation, the phase and the characteristics of the filter and / or the gain of the second exciter (15) with respect to the first are arranged so that when the exciters first and second (13, 15) are excited together, the particularity is softened.
2. 2. A horn according to claim 1, wherein the known frequency is the coincidence frequency.
3. 3. A horn according to claim 1 or 2, wherein the second exciter (15) is arranged separately from the first exciter (13) in the panel (11) at a distance practically equal to an odd multiple of half the wavelength * of the bending waves in the panel, at the known frequency.
4. A horn according to any one of the preceding claims, wherein the first and second exciters (13, 15) are connected in phase, so that the bending waves emitted by the exciters are in phase.
5. 5. A horn according to claim 4, wherein the first and second exciters are connected between common terminals.
6. A horn according to any one of the preceding claims, wherein the panel has first (35) and second (37) axes and the second exciter (15) is separated from the first exciter (13) along the first axis (35) to soften the particularity of coincidence frequency, associated to the bending waves along the first axis (35).
7. 7. A horn according to claim 6, wherein a third exciter (17) is provided separate from the first exciter (13) along the second axis (37) at a distance substantially equal to half the wavelength of the bending waves1 at the coincidence frequency along the second axis (37).
8. A horn according to claim 7, wherein a fourth exciter (19) is provided so that the first (13), second (15), third (17) and fourth (19) exciters define a rectangle on the surface of the panel (11).
9. 9. A bending wave horn comprising: a panel (11) capable of supporting bending waves, a first driver (13) mounted on the panel to excite the bending waves in the panels to produce an acoustic output, in where the response to the acoustic output of the panel (11) excited by the first exciter (13) has a parity at a known frequency, and a second exciter (15) mounted on the panel to excite the bending waves in the panel (11) and produce an acoustic output, wherein the position, separation, orientation, phase characteristics of the filter and / or the gain of the second exciter (15) with respect to the first are arranged so that when the first and second exciters (13) , 15) are excited together, the particularity is softened, wherein the second exciter (15) is located near the first exciter (13) and connected in counter phase with it.
10. A horn according to any one of the preceding claims, wherein a filter is provided in association with one of the first and second exciters to selectively pass frequencies in a predetermined frequency band around the known frequency, through the associated exciter.
11. 11. A horn according to claim 10, wherein the filter is a band pass filter (81) in series with the associated exciter.
12. A horn according to any of the preceding claims, further comprising a higher frequency driver (21) for driving the frequencies above a predetermined cutoff frequency and a divider circuit (20) for feeding the frequency driver (21) higher with the frequencies above the cut-off point and the other exciters (13, 15, 17, 19) with frequencies below the cut-off point.
13. 13. A bending wave horn comprising: a panel (11) capable of supporting bending waves, first and second exciters (13, 15) mounted on the panel (11) to excite the bending waves in the panel and produce an acoustic output, where: the first and second exciters (13.15) are separated by a half-wavelength distance at a predetermined frequency, so that when the first and second exciters are excited together, the acoustic output of the panel is affected at the predetermined frequency.
14. 14. A horn according to claim 13, wherein the first and second drivers (13, 15) are connected in counter phase to increase the acoustic output at the predetermined frequency.
15. 15. A horn according to claim 13, wherein the first and second exciters (13, 15) are connected in phase to reduce the acoustic output to the predetermined frequency.
16. 16. A horn according to claim 15, wherein the known frequency is the coincidence frequency.
17. 17. A horn according to claim 15 or 16, wherein the first and second exciters (13, 15) are connected in phase, so that the bending waves emitted by the exciters are in phase.
18. 18. A horn according to claim 17, wherein the first and second exciters are connected between common terminals.
19. 19. A horn according to any of claims 15 to 18, wherein the panel has first (35) and second (37) axes and the second exciter (15) is separated from the first exciter (13) along the first axis ( 35) to soften the particularity of the coincidence frequency associated with the bending waves along the first axis (35).
20. 20. A horn according to claim 19, wherein a third exciter (17) is provided separate from the first exciter (13) along the second axis (37) at a distance that is practically equal to half the wavelength of the waves bending at the coincidence frequency associated with the second axis (37).
21. A horn according to claim 20, wherein a fourth exciter (19) is provided so that the first (13), second (15), third (17) and fourth (19) exciters define a rectangle on the surface of the panel (11).
22. 22. A horn according to any of claims 13 to 21, further comprising a filter (81) associated with one of the first or second drivers for selectively passing frequencies of a predetermined frequency range around the predetermined frequency.
23. 23. A horn according to any of claims 13 to 22, further comprising an exciter (21) of higher frequency to excite frequencies above a predetermined cutoff frequency and a divider circuit (20) to feed the exciter (21) of higher frequency with the frequencies above the cut-off point and to the other exciters (13, 15, 17, 19) with the frequencies below the cut-off point.
24. 24. A method for suppressing a particularity in the frequency response of a bending wave horn having a panel (11) capable of supporting bending waves and a first exciter (13) mounted on the panel, which includes: determining a frequency at which the response of the first exciter of the panel has a particularity, providing a second exciter (15) in the panel, arranged in such a way that when the first and second exciters (13, 15) are excited together, it softens the particularity
25. 25. A method according to claim 24, wherein a second exciter is provided in the panel at half the length of the bending waves of the panel at the known frequency.
26. 26. A method according to claim 24 or 25, wherein the step of determining the frequency determines the coincidence frequency associated with a predetermined address.