JP2002524994A - Panel-shaped acoustic device using bending wave mode - Google Patents

Abstract

(57) [Summary] A panel-shaped acoustic member capable of supporting bending wave vibration has a bending wave velocity that changes in a coincidence region, and causes acoustic coupling of bending waves in a panel at a wider angle or causes coupling. Provide a coincidence frequency range for more uniformity. This member can be incorporated in a loudspeaker having a panel member (1) and an exciter (3) fixed to the panel member and exciting the bending wave in the loudspeaker to generate an acoustic output.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a panel-shaped acoustic device using a bending wave mode, and more particularly, to a loudspeaker incorporating the panel.

BACKGROUND OF THE INVENTION Distributed mode acoustic devices are known in several documents, such as WO97 / 09842. The device does not operate by moving a diaphragm, such as a normal loudspeaker, back and forth (by piston motion), but rather has a transducer coupled to a rigid panel capable of bending wave vibration. The bending wave vibration is distributed in a required frequency band and couples to the atmosphere. This technique is often used in loudspeakers, where the transducer is an exciter that causes bending wave vibrations that result in acoustic output in the panel.

WO 98/39947, published after the priority date of the present invention, describes a distributed mode acoustic device which can also be operated with piston movement. To place the center of mass at the appropriate exciter location, the flexural stiffness distribution is arranged such that the flexural rigidity center is offset from the exciter location.

In many cases, it is advantageous to use rigid panels. High rigidity panels provide good high and low frequency characteristics. However, when the coincidence frequency is exceeded, the propagation speed of the bending wave at that frequency coincides with the speed of sound in the atmosphere, and strong beaming may occur. The problem of the coincidence effect is small for small panels. However, when the size is reduced, the low frequency characteristics are attenuated and the mode density at a low frequency is reduced, so that uniform response cannot be obtained.

[0005] Low stiffness panels can be used to reduce the coincidence effect. This has a negative effect on the high frequency characteristics in two respects. First, the coil mass can have a strong effect at low frequencies because the impedance is equivalent to the impedance of the panel, affecting high frequency roll-off. Second, the aperture resonance of the panel material inside the voice coil, which occurs when the panel wavelength becomes equal to the diameter of the exciter, occurs in the low-rigidity panel at a low frequency. This effect is clearly seen as the peak of the sound pressure. Furthermore, the low-frequency characteristics of large panels with low rigidity are relatively poor.

DISCLOSURE OF THE INVENTION According to the present invention, there is provided a panel-shaped acoustic member capable of supporting bending wave vibration, wherein a flexural rigidity and / or an areal mass density of a panel is changed over the entire panel area to at least 1. Producing a coincidence frequency range with a 2: 1 maximum: minimum coincidence frequency ratio allows bending waves in the panel to be more uniformly to the atmosphere with respect to acoustic power and / or directivity than isotropic panels. Be combined.

In an embodiment, a 1.2: 1 coincidence range provides a modest effect. However, a wide range of at least 1.5: 1, or preferably at least 2: 1 can provide greater effect.

[0008] Coincident control is not a subject taught in theory or textbooks. The coincidence effect is known but difficult to avoid. Another method is taught to add mass to a member or to laminate damping coupling, but is generally an isotropic treatment.

The panel-shaped acoustic member can be incorporated into any of a number of possible acoustic devices. Accordingly, it is possible to provide a support for an acoustic element including a sound absorbing device, a resonance device for reflection control, an acoustic enclosure, or such a panel-shaped acoustic member.

An active device coupled to a panel-shaped acoustic member and having a transducer that converts an electrical signal to a flex wave or a flex wave to an electrical signal in the member represents a promising application. Therefore, it is possible to provide a microphone having the above-mentioned panel-shaped acoustic member and a transducer for converting a bending wave into an electric signal in the member. A particularly promising application is loudspeakers. Accordingly, a member capable of supporting the bending wave in the audible frequency band, and an exciter on the panel member that excites the bending wave in the panel and generates an acoustic output, the bending rigidity of the panel member is equal to the entire area of the panel member. The loudspeaker changes in accordance with the position over which the coincidence effect on the sound output of the panel is smoothed.

[0011] Coincidence effects on sound output include the concentration of sound above the coincidence frequency and discontinuities or peaks in sound pressure or sound power synthesized in all front hemispheres and / or specific directions as a function of frequency. Including. Any or all of these effects can be reduced using the present invention.

A change in flexural stiffness results in an additional change in the acoustic velocity of the panel, ie, a change in coincidence frequency. Therefore, the direction of the acoustic radiation changes over the entire panel. That is, a change in flexural rigidity causes a distribution of radiated sound spread over a large angle, reducing concentration. Further, in the flexural wave panel, the power output as a function of frequency often has a peak or a step, that is, a discontinuity at the coincidence frequency. This irregularity can be smoothed by changing the coincidence frequency. The coincidence frequency is inversely related to the flexural rigidity and usually changes according to the change in the flexural rigidity. Similarly, it can be changed by changing the thickness of the panel.

[0013] Since the open resonance caused by the coupling of the coil mass to the finite region occurs at a high frequency, advantageously for a rigid panel, the panel can be thicker at the exciter.

On the other hand, the flexural rigidity has a maximum value near the position of the exciter. For example, since the panel can be made symmetrical about its maximum, the optimal off-center position for the distributed mode panel is that the coincidence frequency, which is usually the maximum flexural rigidity, is near the minimum. And not at the position of the minimum. "Near the minimum" means sufficiently close that the flexural stiffness at the exciter location is at least 70% of the maximum, preferably 80%, more preferably higher than 90%.

[0015] In another embodiment, the panel edges are more rigid than the center. The coincidence frequency is still smoothed by the change in stiffness. The exciter can be located in a thin area of the panel where the mechanical impedance of the panel is smaller. This helps to couple less frequency energy to the panel. The panel may have a maximum flexural rigidity in a central region (a region that is one-third in both the vertical and horizontal directions from the center of the panel), and the rigidity may be reduced toward an edge. Such a panel can be formed by injection molding from a thick central region of the panel.

The present invention can provide the advantages of rigid panels while reducing some disadvantages, especially the effect of coincidence frequencies in the audible frequency band. However, the present invention can be applied not only to a large-sized high-rigidity panel but also to a small-sized panel described below to achieve good results.

In order to have an effect on coincidence, the flexural rigidity needs to change over the entire panel having a length dimension equal to or larger than the sound wavelength of the target frequency band. This is typically 3-4 cm at a frequency of 10 kHz. Therefore, a small area with increased flexural rigidity is not suitable for smoothing the coincidence effect. Thus, a change over an area of at least 1.5, preferably twice the wavelength of the coincidence is appropriate. To reduce the coincidence effect, a change over an area of at least 5%, preferably 10% of the panel area is beneficial.

Assuming the above description, the change in bending stiffness can be concentrated on the position of the exciter. For example, the slope of the flexural rigidity may be large near the exciter position and gradually decrease along a line extending outward from the exciter position. In some embodiments, this profile effectively smoothes the coincidence effect. The slope can be reduced to zero at the end of the exciter area, and the change can extend to the panel edge. Since all changes in flexural stiffness are concentrated in the exciter region, the flexural rigidity is constant in regions far from the exciter.

The flexural rigidity can be changed even in the strip near the edge of the panel member. The flexural stiffness may be greatest at the edge and decrease toward the plane inside the panel, or may be minimal and increase at the edge. Such panels may have edges clamped to the frame. The change in flexural stiffness at the edges results in a desired match or mismatch between the mechanical impedance of the panel and the mechanical impedance of the clamp to further control acoustic output.

The flexural stiffness may vary, especially in the end strip at a distance not more than 10% of the length of the panel from the edge. When the rigidity near the panel edge decreases, the mechanical impedance of the panel in the edge region decreases. If this reduced impedance is less than the impedance of the clamp frame, little energy is transferred from the panel to the frame.

Similarly, as the rigidity of the peripheral portion increases, the mechanical impedance of the panel in that region increases. If the panel is supported on a resilient support, increasing the impedance of the panel can create large mismatches and minimize unnecessary energy transfer to the frame. Conversely, when the panel is connected to the rigid clamp frame, it results in a smoother transmission from the panel to the clamp end and assists in the mechanical strength of the final structure. Further, in each case, a sudden change in the bending stiffness near the edge can reflect acoustic vibration energy in the panel, and almost no energy reaches the frame.

The flexural stiffness may change abruptly in the edge region and be relatively constant inside the panel. Alternatively, the deflection stiffness may vary over both the edge region and the inside. In a region where the rigidity between the edge region and the exciter region hardly changes or is zero, the flexural rigidity may change in both the exciter region and the edge region.

As another option, the entire panel may be corrugated or a plurality of steps to change the flexural rigidity. Coincidence frequency f _c of the frequency speed of sound in air matches the speed of the panel
Can be expressed by the following equation. Here, c is the speed of sound in the atmosphere, μ is the area density of the panel, and B is the flexural rigidity.

In practice, any parameter that changes the panel speed as well as, or instead of, the flexural stiffness may be changed, and the coincidence frequency changes accordingly. Therefore, it is possible to change the Young's modulus of the skin and the surface density of the core.

In another aspect, there can be provided a method of making an acoustic member capable of supporting bending wave vibrations, particularly where the wave speed changes in the coincidence region to generate a coincidence frequency range. The method further includes selecting a panel material and panel dimensions, selecting an initial flexural stiffness of the panel profile, and repeatedly varying the tensile stiffness with respect to the area of the panel profile or skin, wherein the panel has a panel frequency near the coincidence frequency. By generating the coincidence frequency range by changing the wave speed of the panel, the frequency response and the angle response of the panel can be improved. In the step of repeatedly selecting the panel profile, the resonance mode distribution with respect to the panel frequency can also be optimized.

In another aspect of the invention, selecting a panel material, panel dimensions and exciter type, selecting an initial exciter position on the panel, and selecting an initial flexural stiffness profile for the panel. A step of repeatedly changing the exciter position and the panel profile to select a position and a profile to optimize the frequency response and the angle response of the panel to reduce the coincidence effect compared to the flat panel; There is provided a method of making a loudspeaker system comprising the steps of providing a panel of a defined panel profile and repeatedly fixing an exciter at a selected position.

The dimensions, profile and exciter location can be selected to provide a distributed mode loudspeaker with the low frequency modes optimally distributed in frequency and the aperture effect at high frequencies minimized. Particular embodiments of the present invention will now be illustratively described with reference to the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 1 shows a loudspeaker having a panel (1) and an exciter (3) attached thereto. The exciter (3) excites a resonant bending wave in the panel to emit sound from the panel. An electrical conductor (5) connects the exciter to the amplifier. In this embodiment, the panel (1) is made of a core (2) and two skins (9). Alternatively, the panel may be integral.

The panel used for the loudspeaker is a distributed mode panel described in an application such as W097 / 09842, and an effective frequency response can be obtained by uniformly distributing the resonance mode with respect to the frequency. It is advantageous if the modes are distributed over the entire panel.

The shape of the panel and the position of the exciter can be selected so as to obtain a good mode distribution of the excitation wave. WO 97/09842 teaches certain suitable shapes, for an isotropic panel, for example, an aspect ratio of 1: 0.882 or 1: 0.707.
Depending on the panel thickness profile, this ratio may require some adjustment.

The position of the exciter is also important. The position of the exciter should be paired with the distributed resonance mode. Some suitable exciter locations are located near but not in the center of the panel. With respect to the isotropic rectangular panel, one of the positions is a coordinate position indicating the length of the side at (3/7, 4/9) close to the center coordinates (1/2, 1/2) of the panel. . Of course, the preferred coordinates for panels with varying flexural stiffness expected in the present invention will be different from this value, but any can be a good starting point for finding the optimal position by trial and error. Alternatively, laser or computer analysis helps identify valid exciter locations.

A cost-effective method of manufacturing flexural panels is injection molding. This reduces unit cost and achieves consistent results, and is also a particular configuration of the mounting of the panel to both the exciter and the panel support frame, with the fixed mounting being molded as an integral part of the panel It may be included in an object, and the cost of parts and assemblies can be reduced. Injection molding can be expected to be effective for panels that are thicker in the center and inclined toward the edges.

By the way, one of the parameters that is considered useful for controlling distributed mode loudspeakers is the coincidence frequency, mainly where it is located in the frequency spectrum. The reason is that above the coincidence, the panel operates under another, less intense, radiation type. Coincidence frequency f _c may be in the audible frequency band for some practical bending wave panels often can adversely affect the listening. At the coincidence frequency, the acoustic radiation is emitted more strongly at a wide angle, the angle becoming narrower towards the normal axis at higher frequencies. If the radiation angle changes from below the coincidence to beyond it, a spatial energy shift occurs, which is not preferable. In addition, the aperture effect limits the high frequency characteristics of the low rigidity panel. Clamped distributed mode loudspeakers allow the use of low stiffness panels, but adding mass density is generally not preferred as it results in efficiency losses.

It is desirable to suppress the adverse effect of the coincidence frequency by changing the flexural rigidity of the entire panel to expand the frequency range and reduce the amount of energy at a single frequency. The net effect is a smooth change over a wide range of coincidences, rather than a sudden change in the high energy content radiation pattern.

As the bending stiffness changes over the entire panel, the wavelength of the bending wave in the frequency range near the coincidence changes over the entire panel. For example, when the thickness increases from the center to the outside, the wave speed increases as approaching the panel end. Conversely, when the inclination is in the opposite direction, the wave speed becomes slow. This changes the eigenvectors associated with the bending waves over the panel surface area.

The slope of the panel stiffness can be changed in various ways. Appropriate methods include the following. 1. The thickness of the entire panel is changed by foaming processing of injection molding. FIG. 2 shows some variants of this method. Adding thickness adds some mass. The stiffness changes abruptly with a change in thickness compared to a very small change in the mass with a change in thickness (the foam mass density is very small). Therefore, the additional mass associated with the added stiffness should be small. 2. When using an integral molding, a rigidity gradient and a surface density gradient can be used (
(See FIG. 2). In this case, doubling the thickness increases the stiffness eight times,
The surface density can only be doubled. Therefore, this is still a viable method for a single entity.

[0037] 3. The generation of the rigidity gradient can be realized by compression-molding a foamed material such as a rohacell material, that is, a sandwich structure having a skin that seals the foamed core, into a desired shape. In this case, the mass density can be maintained over the entire panel surface. 4. The generation of the rigidity gradient can be realized by using a so-called “smart polymer” having a coefficient gradient along its size and area. Variable area or area stiffness polymers can be utilized in sheet form for use in laminated composites, or can be used in injection molding and other manufacturing processes. In this case, the panel can maintain a uniform thickness while achieving a desired rigidity gradient without affecting the mass.

[0038] 5. Use of Panel Profile, Curvature or Corrugation This technique can provide a moderate stiffness gradient unless extremely small radii of curvature are used. This method is practical for applications where "shape" requirements can be combined with styling. See Figures 22 and 23. 6. The core can be milled or polished to the desired profile. The skin may be attached to either side of the milled or polished core. The injection molding method
It is very well suited for producing flexural panels in large quantities at low cost and in a consistent manner. Integral radiators are relatively easy to mold, but may not be suitable for some applications.

[0039] These steps solve the problem of molding in a "no additional cost" manner since the foam molding requires relatively little additional material. When the stiffness changes by 2, the coincidence frequency increases by about 40% (for example, from 10 kHz to 14 kHz),
This is very useful and sufficient to extend the coincidence frequency / energy for many applications.

Several possible flexible panels having such a change in stiffness are shown in FIG. A suitable method for shaping is to vary the thickness outward with a positive or negative gradient. By adjusting the blowing agent in the core of the panel, a large stiffness gradient can be created across the panel. In an integrally formed panel, the stiffness varies in proportion to the cube of the thickness, and in a sandwich panel, the stiffness varies in proportion to the square of the thickness.

If the stiffness gradient changes in a negative direction toward the panel edge, one or more of the following advantages may be obtained. First, since the rigidity near the center of the panel is high, the opening effect due to the finite size of the excitation coil can be reduced. Secondly, it is useful for certain applications, but provides something close to a free support panel that has the advantage of smoothly changing relative to the panel support or frame. Third, it becomes possible to perform injection molding injecting from the center of the panel. This allows a low mass foam core to be made. On the other hand, if the stiffness gradient changes in a positive direction toward the panel edge, the design can be stiffer, providing a smoother change to the edge clamped panel design. This can increase the mechanical robustness of the final structure.

Excitation of the panel can be achieved using any desired method, for example, as described in the applicant's earlier application. In other words, the panel mode is excited uniformly,
The aim is to achieve sufficient smoothness for mechanical impedance (with respect to mechanical force input) and / or acoustic radiation power within the design bandwidth. Such an optimized position can be obtained by analysis or experience of the FE method or the like.

The behavior of bending wave panels is clearly characterized by bending waves at low frequencies, where the panels have a constant bending stiffness and mass density. However, effects at high frequencies, such as coincidence and aperture resonance, can cause deviations from predicted values based on static calculations. This is because at high frequencies, the panel operates with large shear forces that can be characterized by a decreasing flexural stiffness at high frequencies. The exact behavior at high frequencies can only be identified by a thorough understanding of the shear properties of the panel material and is not always available. Thus, the results derived from the basic equation for constant flexural stiffness may not reflect the true behavior for a particular panel material near coincidence. In order to specify the acoustic characteristics of the panel according to the present invention, vibration analysis and experiments are required.

The sound output is the integrated value of the sound pressure level at all angles. The characteristic that is a frequency smoothing function is often a factor related to sound quality. The irregularities in the power output of the flexing panel at the coincidence spread in frequency by ramping the panel thickness. When the rigidity away from the excitation point increases, the coincidence spreads to a low frequency band, and when the rigidity decreases, the coincidence spreads to a high frequency band.

Assuming a large lightweight panel, when the radiative coupling strength increases above the coincidence, most of the energy input to the panel is radiated near the excitation position. As it moves away from the exciter, the panel speed gradually decreases and a small output is emitted. Therefore, it is necessary to concentrate the change in panel thickness relatively close to the exciter, otherwise the change will occur in the panel portion that does not radiate strongly and is less affected. Furthermore, this has the advantage that the change in performance at low frequencies is reduced by the change in panel thickness. That is, at low frequencies (below coincidence), the radiation efficiency is significantly reduced and can be in the form of resonant bending wave modes where energy is distributed over the frequency and the entire panel surface.

On the other hand, in a heavy panel, the radiation coupling is small and sound is radiated over a wide area of the panel. Therefore, the change in rigidity / wave velocity needs to be concentrated in a wide area. The region to which the change is assigned for the same reason will also depend on the damping of the structural material if the damping of the structural material is greater than the radiation damping.

In summary, the required profile to extend the coincidence effect depends on the panel's mass density, flexural stiffness, shear and damping properties.

In principle, when the flexural rigidity of the panel changes, the directivity also changes. For panels whose stiffness is reduced from the location of the exciter, the acoustic radiation can spread at a wide angle perpendicular to the panel. Conversely, for stiffer panels, the acoustic radiation can spread at a narrow angle perpendicular to the panel. In any case, the angle range is wide. In practice, the directivity of the radiation from the panel is much more difficult to smooth than the acoustic output, as described below. Assuming that the speed of the radiation concentration exceeding the coincidence from the panel portion is V _panel , the beam angle from the on-axis position can be obtained by the following equation.

At certain frequencies, different parts of the panel radiate in different directions at different bending wave velocities, resulting in a specific polar coordinate system of acoustic energy as a function of orientation. According to the above equation, as the frequency increases, the panel speed increases, and the angle of the radiated sound decreases toward the axial position. The differential value of the angle with respect to the speed is large at a large angle, and becomes smaller as the angle becomes smaller toward the on-axis position. Thus, at higher frequencies, sound is emitted in a deformed pattern. Energy is concentrated in a narrow beam near the normal axis.

As the frequency increases, the shape of the polar coordinate system changes. The apparent change in flexural stiffness across the panel allows for a more uniform acoustic output for a given frequency, but at other frequencies the aggregate power produces a less smooth output. On the other hand, the sound pressure level at one listening angle can be adjusted to be relatively constant. However, the sound pressure elsewhere may no longer be constant and exhibit a high concentration effect.

In summary, it is not possible to obtain a maximum smooth polar coordinate system for all frequencies, or a maximum smooth frequency response for multiple points. Designers need to find a useful compromise that provides a relatively smooth response over a range of points and a relatively smooth polar coordinate system over a range of frequencies.

Experimental Results The panels tested in FIGS. 4 to 10 show that the uncompressed Rohacell material was
It has an m-thick glass skin. The graded panel was formed by laminating the skin on a Lohacell plate polished to the desired profile. Relatively large panels were chosen to accentuate the coincidence effect and the dimensions were as follows: (Intermediate demonstration size) Panel length: 544 mm Panel width: 480 mm Panel area: 0.26 m ²

To simplify the test panel profile, the excitation point selected was at the center of the panel. As the exciter, a 4-ohm electrodynamic exciter with a 13 mm diameter voice coil manufactured by NEC was used.

The following measurement was performed for each panel. (1) Sound pressure level as a function of the angle around the panel Measured distance = 1 m Baffle panel Total area = 1 m ^{2 The} results are shown in dB. Data is not smoothed. (2) Single frequency polar coordinate system for indicating directivity Measurement distance = 1 m Baffle panel Total area = 1 m ^{2 The} results are shown in dB. The data was smoothed by three octaves to smooth out the fine variation characteristics of the flex panel radiation and to emphasize the coincidence aspect. (3) Sound output Measurement distance = 1 m Baffle panel Total area = 1 m ^{2 The} results are shown in dB. Data is not smoothed. (4) Excitation point velocity measured by laser velocity system The results are given in units of mm / s / V. Data is not smoothed. (5) Scanning of panel velocity distribution over the entire panel The panel was used to measure the wavelength in the panel and the bending velocity at a predetermined excitation frequency.

First, results of a comparative panel having a predetermined flexural rigidity will be described. FIG. 3a shows bending wave velocities calculated from the material parameters of three uniform thickness panels of 4 mm, 3 mm and 2 mm respectively. FIG. 3b shows the results of experiments on panel speeds of these panels, which were obtained from images of vibration patterns in the panel at a constant frequency. At low frequencies, the predicted values agree with the experimental results. However, at higher frequencies, the measurement speed is less than expected due to the effects of shear. The change in velocity with frequency is more gradual than the square root correlation expected for a pure bending wave at higher frequencies.

The line labeled “c” in the graph of FIG. 3 represents the speed of sound in the atmosphere. The frequency at which this line intersects the speed trace for each panel thickness is the coincidence frequency. The predicted / calculated value from static or low frequency flexural stiffness is 4 mm for panel thickness.
from 2 mm to 2 mm, the coincidence frequency increases from about 5 kHz to 8.5 k.
Hz. In fact, this change in thickness causes the coincidence frequency to increase significantly from 5 kHz to 14 kHz. 5k for 4mm thick panel
A 3 mm thick panel had a coincidence frequency of 7 kHz, and a 2 mm thick panel had a coincidence frequency of 14 kHz.

The below-described sloped panel has a thickness of 4 mm at the excitation point and reduced to 2 mm at the edge. The coincidence effect solved by the present invention is shown in FIGS. 4 to 6 and shows a measured value on a flat panel having a thickness of 4 mm.

FIG. 4 shows measurements of single point frequency responsiveness on axis, 40 degrees off axis and 80 degrees off axis. As the angle increases away from the on-axis position, the lower frequencies are attenuated due to acoustic cancellation. At 80 degrees, a high frequency peak occurs at 5 kHz, the coincidence frequency of this panel. The peak acoustic power at 80 degrees reaches 80 dB, which is about 14 dB greater than the on-axis response at this frequency. This peak of responsiveness according to the degree of damping is characteristic of the coincidence effect of the rigid panel.

FIG. 5 shows a polar coordinate system of sound pressure levels in various directions at 6 kHz, 9 kHz and 15 kHz. The emission angle is clearly narrower, starting at 90 degrees at 6 kHz and down to less than 60 degrees at 15 kHz. The higher the frequency, the narrower,
Radiation concentration at an angle is characteristic of the coincidence effect.

FIG. 6 shows the sound output as a function of frequency. The output changes gently at low frequencies. However, as the frequency increases, the output rises to a maximum near the coincidence frequency and then falls at higher frequencies. The maxima are much wider than those seen in the sound pressure level trace of FIG. This is because the output measurement is the integrated value of the sound pressure level over all angles and reflects only the total value of the sound output that changes relatively slowly with respect to frequency without reflecting the changing directivity. .

Hereinafter, a first embodiment of the loudspeaker according to the present invention will be described. The loudspeakers have sloped panels. FIG. 7a shows the profile of the sloped panel as a function of the distance ratio to the panel edge. The panel is milled to this profile in both the x and y planes, with a central pyramid shape. FIG. 7b shows a graph corresponding to the coincidence frequency, and there is a large change near the exciter. FIG. 8 shows the single frequency response when the angle is increased around the panel. The on-axis response is the same as the reference panel for high and low frequency extension.

In this embodiment, the coincidence maximum indicated by the flat panel is attenuated by up to 10 dB. The width of the maximum value is also approximately doubled. Above the coincidence frequency, the on-axis response observed in the comparative example was 80%.
The large attenuation of the sound pressure level in degrees is not seen in the panel according to the present embodiment, and the off-axis response at high frequencies is considerably improved.

FIG. 9 shows a polar coordinate system of sound pressure levels at 6 kHz, 9 kHz, and 15 kHz, which is the same as that shown in FIG. Comparing these two figures, it is clear that the polar system beaming of the panel according to the first embodiment is considerably smaller than the reference flat panel.

FIG. 10 shows the acoustic output radiated by the panel of the first embodiment. FIG.
When compared to the responsiveness of the reference panel shown in Figure 7, it is clear that the coincidence maxima are attenuated by 5 dB and spread to higher frequencies, as expected for a graded panel with less stiffness toward the edges. .

In summary, the test panel shows a significant improvement over the flat panel in all of the problems due to coincidence. Thus, each problem of coincidence presents an appropriate compromise of the panel profile with greatly improved, while maintaining good frequency characteristics.

FIGS. 11 to 14 show the results for a loudspeaker according to a second embodiment of the present invention in which the gradient varies significantly over the panel area. The result is shown in FIG.
Very similar to the panel results. Both panels show a suitable compromise that improves on all issues of coincidence emission characteristics. The second panel shows a slight improvement in single frequency polar system results over the first panel, but a slightly reduced series of single frequency response and acoustic output traces. . Optimization is always a compromise, but the designer can choose according to the requirements of the application.

The first two embodiments relate to medium-sized panels. In the third embodiment, a small panel (A5-210 × 148.5 mm) is examined. 15 and 16 show panel profiles. It can be seen that this has a large gradient. The panel is made of 14.5 mm thick Rohacell material, compressed to 10.8 mm at the center and 1 mm at the edges. The entire surface of the inspection flat panel is compressed to 9.8 mm. The exciter is mounted on the back of the panel at the optimal position for the isotropic panel. You could assume a more optimal position of the exciter,
Good results were obtained for the sloping panel at this exciter position.

FIG. 16 shows a coincidence frequency plot calculated as a function of the position of the entire panel. FIG. 17 shows a comparison result between a flat panel having the same dimensions and a thickness of 10 mm and a panel having a slope. Sound power measurements are shown in FIG. 18a (flat panel) and FIG. 18b (graded panel). As shown, the panel has a very wide directivity, and even at 13 kHz, sound is uniformly radiated to the front hemisphere. Also, the output response of the graded panel does not show significant steps around 5 kHz. Such a step is clearly visible in the response of the reference panel. These test panels are mounted in a shallow box and have approximately 50
Note that we raise 0 Hz to the maximum value. This needs to be controlled in real loudspeakers by electric filters or other methods. This is due to the box, not the gradient.

A number of tests were performed on other panels. The results show that various effects of the coincidence of the panel according to the present invention are improved. The profile is important for smoothing out the effects of directivity, but the precise profile is less important for achieving total sound output.

FIGS. 19 to 21 show the measured values of the driving point velocities of three panels excited using a converter having a 25 mm diameter voice coil. 19 shows the result of the 4 mm flat panel, FIG. 20 shows the result of the panel of the first embodiment, and FIG. 21 shows the result of the 2 mm flat panel. The sharp resonance between 10 kHz and 20 kHz in the velocity trace clearly shows the aperture resonance. The resonance of the 4 mm panel and the sloped panel occurs at 13.1 kHz. The resonance of the 2 mm panel occurs at 11.8 kHz.

As expected, the resonance frequency of the flat panel increases as the panel rigidity increases. The resonant frequency of the graded panel can be determined from the panel thickness at the driving point and is therefore the same as a 4 mm thick panel. This indicates that the aperture resonance can be determined from the panel thickness at the driving point. Therefore, the presence of the rigid panel area at the exciter position minimizes this aperture resonance.

The results (not shown) also show that if the change in flexural rigidity is concentrated around the panel edge, the effect on the radiation characteristics above the coincidence frequency is small. However, treating the panel that way may be advantageous, as described below. To make a practical loudspeaker, the panels are often mounted on specific frames / supports. The purpose is to maintain the resonance energy in the panel to minimize transmission to the frame. This is achieved by a large impedance mismatch between the panel and the frame. By varying the panel thickness at the edges, the impedance at the panel / frame boundary can be adjusted without significantly affecting the overall radiation characteristics. This method offers a few advantageous embodiments.

When a gradient is applied to the panel so that the thickness near the edge is very small, the impedance of the panel can be made very small. If this impedance is sufficiently lower than the mounting frame impedance, only a small amount of energy will be transferred. If the thickness of the panel is increased at the edges, the impedance will be significantly higher. If the panel is coupled to a soft (and correspondingly low impedance) termination frame,
The impedance of the panel will be high and there will be a large mismatch at the boundary, minimizing energy transfer to the frame.

In addition to the above two examples, if the panel thickness at the boundary is rapidly increased / decreased, energy should be reflected back to the panel body. For example, an abrupt increase in panel thickness at the edge will provide an analogy to the clamp boundary and reflect incident energy back into the panel. The edges can be safely clamped or supported there to contain only small vibrations.

It is not necessary to change the panel thickness to obtain a change in flexural rigidity. FIG. 22 shows a panel where the thickness is constant but the radius of curvature varies over the entire panel area. This changes the deflection stiffness. Another method is shown in FIG. As shown, the panel is corrugated and the flexural stiffness is greater at the center than at the outside.

Further, it is not necessary to change the panel thickness by the simple method described above. For example, the flexural stiffness can be changed by forming a wavy pattern over the entire surface or by making the entire panel surface a continuous step. FIG. 24 shows a few possible profiles. Such a profile can be obtained with similar wavy ridges or steps in the thickness of the panel, or otherwise.

[Brief description of the drawings]

FIG. 1 shows a loudspeaker according to the invention.

FIG. 2 shows a profile of a panel used in a loudspeaker according to the invention.

FIG. 3 shows sound speed and sound output from a loudspeaker of uniform thickness for comparison.

FIG. 4 shows the speed of sound and sound output from a loudspeaker of uniform thickness for comparison.

FIG. 5 shows sound speed and sound output from a loudspeaker of uniform thickness for comparison.

FIG. 6 shows the speed of sound and sound output from a loudspeaker of uniform thickness for comparison.

FIG. 7 shows parameters of the loudspeaker according to the first embodiment of the present invention.

FIG. 8 is a result obtained using the loudspeaker shown in FIG. 7;

FIG. 9 is a result obtained by using the loudspeaker shown in FIG. 7;

FIG. 10 is a result obtained by using the loudspeaker shown in FIG. 7;

FIG. 11 shows parameters of the second embodiment of the present invention.

FIG. 12 is a result obtained by using the loudspeaker shown in FIG. 11;

FIG. 13 is a result obtained by using the loudspeaker shown in FIG. 11;

FIG. 14 is a result obtained by using the loudspeaker shown in FIG. 11;

FIG. 15 shows a third embodiment of the present invention.

FIG. 16 shows a coincidence frequency change that changes over the entire panel of FIG.

FIG. 17 shows the results obtained using the loudspeaker of FIG.

FIG. 18 shows the results obtained using the loudspeaker of FIG.

19 shows the effect of aperture resonance in the panel shown in FIG.

20 shows the effect of aperture resonance in the panel shown in FIG.

21 shows the effect of aperture resonance in the panel shown in FIG.

FIG. 22 illustrates another method of changing flexural stiffness.

FIG. 23 illustrates another method of changing flexural stiffness.

FIG. 24 shows another panel profile.

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] October 11, 2000 (2000.10.11)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR , BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL , IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (34)

[Claims] 1. A panel-shaped acoustic member capable of supporting bending wave vibration, wherein a bending rigidity and / or an area mass density in a panel changes over the entire surface of the panel, and a maximum value of at least 1.2: 1: Generating a coincidence frequency band having a minimum coincidence frequency ratio, wherein bending waves in the panel are more uniformly coupled to the atmosphere with respect to sound output and / or directivity as compared to an isotropic panel. Panel-shaped acoustic member. 2. An acoustic device comprising: the panel-shaped acoustic member according to claim 1; and a transducer coupled to the member. 3. A panel (1) and an exciter (3) coupled to said panel (1) for exciting a bending wave in said member to produce an acoustic output, said panel being provided. 4. The loudspeaker according to claim 1, wherein a coincidence effect relating to an acoustic output of the panel is smoothed. 4. A loudspeaker according to claim 3, wherein the bending stiffness of the panel (1) varies over an area of at least 10% of the panel area. 5. The panel according to claim 1, wherein the flexural rigidity has a maximum value, and the exciter is coupled to the panel at a position having a flexural rigidity of at least 70% of the maximum value. The loudspeaker according to claim 3 or 4, wherein 6. The panel according to claim 3, wherein the thickness of the panel varies over the entire surface of the panel to provide a flexural rigidity region and thus a coincidence frequency band.
The loudspeaker according to any one of claims 1 to 5. 7. The panel according to claim 3, wherein the flexural rigidity has a maximum value in a central region of the panel, and decreases toward an end. Loudspeaker. 8. A loudspeaker according to claim 7, wherein the exciter (3) is coupled to the panel (1) with a flexural stiffness near a maximum value. 9. A loudspeaker according to claim 3, wherein the exciter is arranged at a position where the flexural rigidity of the panel is at a maximum value. . 10. The panel according to claim 3, wherein the panel stiffness has a maximum value at a central portion of the panel, and increases toward an edge of the panel. A loudspeaker according to any one of the preceding claims. 11. The exciter (3) is arranged in a region near the center of the panel (1) and having a rigidity lower than the average rigidity of the panel (1). A loudspeaker according to claim 1. 12. The panel of claim 1, wherein at least one edge of the panel is clamped, and wherein the flexural rigidity of the panel is maximized at at least one clamp edge. The loudspeaker according to 10 or 11. 13. The loudspeaker according to claim 3, wherein a gradient of flexural rigidity is concentrated near the exciter position. 14. Loud according to claim 13, characterized in that the gradient of the bending stiffness is large near the exciter (3) and gradually decreases along a line extending outwardly from the exciter. Speaker. 15. The loudspeaker according to claim 2, wherein the flexural rigidity changes around an edge of the panel member. 16. The panel according to claim 1, wherein the flexural rigidity is greatest at an edge of the panel, and decreases smoothly toward the inside of the panel.
A loudspeaker according to claim 5. 17. A loudspeaker according to claim 15, wherein at least one edge is clamped to the support. 18. The flexural rigidity at the edge of the panel (1) is less than the flexural rigidity of the panel (1).
A loudspeaker according to claim 17, characterized in that: 1) the mechanical impedance at the edge is mismatched with the mechanical impedance of the support (13). 19. The loudspeaker according to claim 3, wherein the flexural rigidity of the panel changes in a wave-like manner, so that a coincidence effect regarding sound output is smoothed. 20. A loudspeaker according to claim 3, wherein the panel is a distributed mode panel having a plurality of resonant bending wave modes distributed in frequency. 21. A panel capable of supporting a bending wave in an audio frequency range.
And an exciter (3) on the panel (1) for exciting a resonant bending wave in the panel to generate an acoustic output, wherein the coincidence frequency of the panel (1) is A loudness characterized by varying over the length scale of at least one wavelength at the coincidence with the position of the entire surface of the panel (1) to smooth the coincidence effect on the acoustic output of said panel (1). Speaker. 22. The loudspeaker according to claim 21, wherein the flexural rigidity changes over the entire surface of the panel (1), so that the coincidence frequency changes. 23. A panel member capable of supporting a bending wave in an audio frequency range.
1) and an exciter provided on the panel member (1) for exciting a resonant bending wave in the panel to generate an acoustic output, wherein the panel member (1) has a flexural rigidity. A loudspeaker varying in an edge region of the panel. 24. The panel edge according to claim 23, wherein the panel edge is clamped and the flexural rigidity of the panel increases sharply toward the panel edge.
A loudspeaker according to claim 1. 25. A sound absorbing device comprising the panel-shaped acoustic member according to claim 1. 26. An acoustic resonator for reflection control, comprising the panel-shaped acoustic member according to claim 1. 27. An acoustic enclosure comprising the panel-shaped acoustic member according to claim 1. 28. An audio component support comprising the panel-shaped acoustic member according to claim 1. 29. The acoustic device according to claim 2, wherein the transducer converts a bending wave in the panel into an electric signal, and the acoustic device functions as a microphone. 3. The acoustic device according to 2. 30. A method of making an acoustic member capable of supporting bending wave vibrations, particularly wherein the wave speed changes in a coincidence region to generate a coincidence frequency band. 31. A method of making an acoustic member capable of supporting bending wave vibrations, further comprising selecting a panel material and a panel size, selecting an initial bending stiffness of the panel profile, and providing a near-coincidence frequency. 31. The method of claim 30, wherein varying the wave velocity in the panel to generate a coincidence frequency thereby repeatedly changing the flexural stiffness profile of the panel to improve the frequency and angular responsiveness of the panel. . 32. The method of claim 31, wherein in the step of repeatedly selecting the panel profile, the distribution of resonance modes in the panel over frequency is also optimized. 33. selecting a panel material, panel size and exciter type; selecting an initial exciter position on the panel; selecting an initial flexural stiffness profile of the panel; Selecting a position and a profile at which the position and the panel profile are repeatedly changed to smooth the frequency response and the angular acoustic response of the panel; and preparing a panel of the repeatedly selected panel profile. Fixing the exciter in the repeatedly selected position. A method of making a resonant mode loudspeaker. 34. The method of claim 33, wherein the step of repeatedly selecting the exciter position and panel profile also optimizes a resonance mode distribution with respect to frequency in the panel.