KR20010080941A - Acoustic Device according to Bending Wave Principle - Google Patents

Abstract

An acoustic device has an outer shell (1) supporting bending waves and enclosing a volume (2). The bending waves couple to the enclosed volume to provide coupled resonant modes. A transducer (3, 5) is coupled to the shell to excite the coupled resonant modes. The coupling of the enclosed volume can improve the distribution of resonant modes.

Description

Acoustic Device according to Bending Wave Principle}

International patent application WO97 / 09842 and related applications describe another acoustic device having a speaker and a transducer connected to the acoustic member and the acoustic member. In these devices, many of the parameters of the member can be adjusted such that the resonant bending wave mode in the member is often evenly distributed. The resonant bending wave mode may also be distributed evenly on the surface of the member. The preferred position for installing the transducer in the member is also determined. Traditionally, the preferred installation location is not only the center but also the location near the center. Yet another preferred position can be determined depending on the shape of the member.

However, it is not always easy to always provide a sufficient modal density, especially at low frequencies. Thus, it would be useful if improved mode density or other enhancements were provided especially for low or medium frequency responses.

This invention relates to an acoustical device in the form of using members that sustain bending wave operation at the surface of the member and using bending waves that alternately couple with the surroundings. For example, these devices can be used in loudspeakers or microphones.

Specific embodiments of the present invention will be described with reference to the following drawings, which are attached by way of example.

1 is a cross-sectional view of a loudspeaker according to a first embodiment of the invention with an elliptical shell.

2 is a cross-sectional view of a loudspeaker according to a second embodiment.

3 is a cross-sectional view of a loudspeaker according to a third embodiment having a port.

4 is a cross-sectional view of a modification of a port.

5 is a perspective view of a loudspeaker according to a fourth embodiment of the present invention in the form of an open box.

6 is a perspective view of a fifth embodiment of the present invention with a sealed box.

FIG. 7 illustrates various excitation techniques that can be used with the loudspeaker shown in FIG. 6.

8 shows the response to excitation in an open box without air.

FIG. 9 shows the response to excitation in the open box shown in FIG. 8 including the effect of air coupling.

FIG. 10A shows the velocity response at the exciter for the box of FIG. 8 without air as a function of frequency.

FIG. 10B shows the velocity response at the exciter for the box of FIG. 9 with the effect of air as a function of frequency.

FIG. 11 shows the pressure in the box of FIG. 9B.

12 shows modes in a loudspeaker with a closed box with two excitators driven in reverse phase.

FIG. 13 shows the modes in the loudspeaker of FIG. 12 with two excitators driven in phase.

14 shows the velocity response for the device of FIGS. 12 and 13.

15 shows the velocity response of a closed box with six sides where the front bending stiffness does not match the back bending stiffness.

16 is a perspective view of a loudspeaker according to the present invention in a pyramid shape with cut edges.

17 is a perspective view of a loudspeaker according to the present invention in the shape of a tetrahedron.

18 is a perspective view of a loudspeaker according to the present invention in the shape of a dodecahedron.

19 is a perspective view of a loudspeaker according to the present invention in the shape of a cylinder.

20 is a perspective view of a loudspeaker according to the present invention in a conical shape.

FIG. 21 shows the root mean square central difference of the mode frequencies as a function of aspect ratio of the front of the device of FIG. 5.

FIG. 22 is a velocity distribution for the three exciter positions of the device of FIG. 5 with a front aspect ratio of 2: 1.

FIG. 23 shows the shape of the benefits for the exciter position as a function of the exciter position in the device used in the mode for FIG. 22.

According to a first aspect of the present invention, a flexural wave maintains the curved wave in a bent shape to at least partially surround the air volume for coupling with the air volume to provide a coupled resonant mode. An acoustic device is provided which consists of a substantially continuous outer shell and a transducer which is coupled to the shell and then to the ambient sound to couple the electrical signal to the coupled mode.

In the device according to the invention, there are additional modes in addition to the resonant bending wave mode useful in conventional distributed mode devices. Numerical calculations will be described later, indicating the number of increased modes with air coupled to the outer shell. The device according to the invention can thus increase the number of modes present in a predetermined frequency range.

Preferably, the couple resonance mode is distributed at equal frequencies over a predetermined frequency range. In practice, the frequency range is one to two or three octaves higher than the fundamental resonant frequency. In this range, the resonant flexural wave mode is the most sparse and the flexural and planar modes in this distribution have the greatest advantage.

The outer shell may be completely sealed to enclose the volume as a whole. Optionally, ports or vents may be provided on the outer shell. The ports and vents can be designed to provide a pronounced resonant effect and to boost or control the output, especially in the low acoustic frequency range.

Although the outer shell does not need to completely surround the enclosed volume, the outer shell must be substantially continuous in order to exhibit effective sonic action. In other words, the outer shell need not have too many holes or windows. Porous members are not suitable as acoustic emitters because radiation at the front of the member interferes with radiation at the back of the member which is radiated in reverse. Moreover, the shell must be contiguous enough to make the shell bound to the enclosed volume.

Tests on the panel showed that the bond between the ambient air and the porous member was very low. Thus, the outer shell does not occupy more than 20% of the total surface area of the pores, preferably not more than 10% more preferably not more than 5%.

Air in the volume may also exhibit cavity resonance.

The acoustic device according to the invention combines with a volume at least partially wrapped by the shell and maintains a resonant bending wave mode with respect to the surface of the three-dimensional shell. In contrast, the conventional distribution mode loudspeaker has a resonant bending wave mode distributed in one panel.

In WO 97/09842 mentioned above, it is proposed to install a distribution mode panel on the front of the frame. In this prior art device the resonant bending wave mode is confined to the panel region rather than the frame substantially. Thus, such a device does not increase the improved mode density and acoustic performance provided by the present invention.

Another preceding application WO 98/31188 describes a flat panel mounted in a tray. The tray is porous with more windows than the solid area and therefore is not substantially continuous. Thus the tray will not bind effectively to the surroundings and also to the air in the tray.

The outer shell has a constant thickness and can optionally vary slowly or continuously or faster.

Skeleton or other elongate members may be provided in the outer shell.

The shell may be a one-component shell, and optionally the outer shell may consist of a combination of mechanically coupled members to make the desired acoustic emitter structure. Boundary conditions can be usefully specified in the engagement between the members.

The outer shell may be in the shape of a polyhedron and may be a part having a plurality of faces, respectively.

Each face has a natural resonant frequency and the natural resonant frequency can be chosen to have different values. This can increase the modal density of the outer shell as a whole. Moreover, other natural resonant frequencies may be chosen such that there are resonant modes on the inserted frequency on the other side. This method is particularly useful for increasing the mode density in low 10-20 resonance modes.

Panel members separated from the respective surfaces need not have uniform mechanical properties, and stiffness, isotropy of rigidity, and damping also vary in thickness.

The acoustic device may be a loudspeaker, a transducer with an exciter.

The acoustic device may comprise front and rear faces in the form of a panel, and together with at least one panel providing a path for the resonant mode from front to back, thus connecting the front and rear panels. . The front and rear panels are substantially planar, driven by separate exciters and also one exciter can be coupled to both the front and rear panels.

In an embodiment, the excitation voice coil is connected to one of the panels and the magnet assembly of the exciter is connected to the other panel. Since the magnet assembly is heavy, the connection with the panel will cause a high frequency drop. This may increase the bass response of the acoustic device. A plurality of transducers are provided and the exciters can be driven in-phase, out of phase or in a suitable phase relationship with each other.

In conventional flat panel loudspeakers, no in-phase compression wave produces little or no acoustic output. This is because the in-plane compression and expansion of the flat panel do not combine with the ambient air. In contrast, in the device according to the invention, the outer shell is bent so that the compression and expansion on the plane constricts and expands the shell locally or globally, and the expansion and contraction of the shell is intended to couple the compressed wave with the enclosed volume and the surroundings. It acts as a mechanism. Therefore, the compressed wave on the plane will be usefully contributed to the coupling mode. In fact, the resonant mode may be combined with flexural waves, in-plane mode and enclosed volume in some embodiments. Thus, the mode density can be improved.

According to a second aspect of the present invention, a shell is provided to substantially maintain a plurality of resonant modes of combining the shell and the enclosed volume, and to substantially enclose the volume, the resonant mode spanning the shell, and the electrical signal to resonate. It provides a sound device comprising a transducer coupled to and then in turn coupled with the ambient sound.

In the device according to the second aspect of the invention, the resonant mode spans the surface from front to back, side to side and from top to bottom, ideally combining the modes with respect to the entire surface with wrapped volume. The modes do not need to surround the entire surface and may have for example a port or an area that does not resonate.

According to another aspect of the present invention, there is provided a generally continuous outer shell and a shell having a shape that is bent to at least partially surround the air volume to couple the flexion wave to the volume to provide a couple resonance mode. Provided are a method of driving an acoustic device having two transducers comprising driving two transducers in phase with a combined general electrical signal and radiating acoustic energy from the coupled mode into the ambient air. Here, the transducer drives the coupling mode of the shell and the volume in a unipolar shape.

As shown in FIG. 1, the closed oval shell 1 comprises transducers 3 and 5 installed inside the shell in a position surrounding the volume 2 and opposing the minor axis of the ellipse. The shell 1 sustains the resonant modes formed from the resonant bending wave elements coupled to the enclosed volume.

The transducers connect the electrical signal to the coupled resonance mode of the shell and volume. In an embodiment the transducers are excitators that can be usefully driven to excite the couple mode to produce an acoustic output. The transducer may be of a conventional type in which the acoustic coil moves relative to the grounded magnet assembly as electrical current passes through the acoustic coil. The transducer may have inertia if the magnet assembly is free and the force of the acoustic coil acts against the inertia of the magnet assembly. Optionally, a grounded transducer can be used if the magnet assembly persists. Commercially useful transducers used to drive the distribution mode panel in the embodiment are used in one inertial form.

By driving the transducer to a known polarity, it is possible to produce the desired polarity behavior with the injected sound. For a monopole source, the transducers can be driven in phase, while to make a dipole source, the transducers can be driven in reverse. Optionally, the exciters can be driven in an appropriate phase relationship.

The present invention allows loudspeakers to be used without baffles. In a conventional piston-type or distribution mode loudspeaker using one diaphragm or panel, the sound radiated from the rear is inverse to the sound radiated from the front. Therefore, to avoid the interference effect, it is necessary to wrap the box diaphragm or provide a baffle around the loudspeaker so that the sound radiated from the rear cannot reach the front. Such a baffle can be avoided by driving the loudspeaker according to the invention with a single pole having two transducers operating in phase.

Coupled mode may consist of two types of shell vibration coupled to the enclosed volume. One form of these is a flexure wave that bends the shell from its local plane. Another form is expansion or contraction in the plane of the shell.

The flat plate as a whole does not provide a combined expansion-contraction mode with a resonant bending wave mode. Although flat plates may have vibrational modes of expansion and contraction, they simply move the plates to their faces and do not affect the movement of surrounding air molecules. Thus, such modes in the plate have little or no sound effect. On the other hand, if the plate is bent sufficiently backwards by itself or even forms a fully enclosed body, the planar compressed wave mode causes the overall expansion and contraction of the body, which can be combined with air and have an acoustic effect.

The actual mode of oscillation of the shell need not be a pure flexural wave mode nor a pure compressed wave mode. Rather, the modes interfere and combine with each other to provide couple modes. However, these modes still maintain unusual flexural properties. Then in the shell these waves combine with the included volume to create the couple resonance modes.

It is not necessary for the transducers to be installed on the short axis. It may be convenient to install off-axis or at an appropriate location as shown in FIG. 2. It is better to install the transducer in the location chosen for optimal or desired response. It is useful to use certain shapes such as ellipses. Optionally, a finite element analysis approach can be used to investigate the appropriate transducer position. In general, an approach similar to that used for distributed mode loudspeakers would be appropriate. It is particularly suitable for asymmetrical transducer positions. An example of this will be explained later with reference to FIG. 21.

One single converter will suffice for some applications. Other applications may require several transducers mounted on the shell. The installation of the transducer can affect the engagement with the surroundings of the outer shell.

Providing a wrapped volume allows the port to be used to control resonance in the volume. 3 shows the port 7 in the shape of a simple hole at one end of an ellipse. Optionally, the duct port 9 may be provided as shown in FIG. 4.

The port produces an effect similar to that produced in conventional piston loudspeakers or pipes. The ports may have an asymmetric cross section.

As mentioned above, the volume does not need to be entirely wrapped by the shell. Rather, what is needed is that the shell bends itself far enough back so that the shell's resonant mode combines with the enclosed volume of air to produce a sound effect.

FIG. 5 shows an open box comprising a large front face 11 surrounded by a frame 13 consisting of four sides 15 perpendicular to the front face 11. One sole transducer 3 is provided and is connected to an amplifier by an audio connection 9. The sides 15 are all acoustically connected to the front face 11. In the front face 11 the resonant bending wave mode simply connects to the sides 15 instead of remaining in the front face.

The box also has a hermetically sealed shape with a front face 11 and a rear face 17 and four side faces 13 joining the front face 11 with the back face 17 to form a hermetic seal to receive the volume (Figure 3). 6). Two transducers 3, 5 are provided, one on each side 11, 17.

Also shown in FIG. 6 is an electrical circuit 19 for switching the switching and non-switching driving of the two transducers. A double pole double throw switch 21 switches between parallel drive and non-parallel drive of the transducer.

The transducer or the front and the back may not be combined as in FIG. 7A. Optionally, the magnet assemblies of two conventional moving coil transducers can be joined together as shown in FIG. 7B. As an alternative, one single transducer can have an acoustic coil connected to the front face 11 and a magnet assembly connected to the back face 17. The magnet assembly is much heavier than the acoustic coil and therefore the assembly will prefer to couple low frequencies to the back. Thus this arrangement can be used to increase the bass response of the loudspeaker. The front and back side can be changed.

The calculation by finite element analysis of the response of the acoustic device was applied for a device with five sides similar to that shown in FIG. For convenience, this form will be referred to as an open box. FIG. 8 shows the behavior of the box in response to excitation at 178 Hz (FIG. 8A), 348 Hz (FIG. 8B) and 1000 Hz (FIG. 8C) in the presence of air. FIG. 9 shows the behavior at the same frequencies, 178 Hz (FIG. 9A), 348 Hz (FIG. 9B) and 1000 Hz (FIG. 9C) in the presence of air. As can be seen from the figure, the response is not limited to any one of the flat faces, but combined for all five sides of the box. Moreover, the presence of air makes the form more complicated.

10 shows the velocity response as a function of frequency in the transducer. FIG. 10A shows the results when there is no air and 10B when there is air. Larger values indicate the higher velocity generated by the excitation at that frequency. Especially large speeds occur at resonance. As can be seen, the response in the absence of air represents a smaller, larger maximum. This is indicative of a smaller number of resonance modes. The presence of enclosed air indicates a greater number of maximums and each value is smaller. This is a characteristic of having more weaker modes. As can be seen, the coupling of the modes to the enclosed volume in the panel increases the number of resonant modes and thus improves the acoustics. Surprisingly, this effect is even seen in open boxes.

11 shows the air pressure in the box at 348 Hz. Asymmetric air pressure forms are clearly seen. This air pressure distribution causes a complex mode shape of the air combined with the resonance mode.

Similar calculations were performed for an acoustic device similar to that shown in FIG. 6, namely a closed six-sided box with front, back and four sides. Some of these results are shown in FIGS. 12 and 13. All calculations include air. In other words, couple mode combines for all surfaces of the box (front and back, left and right, up and down).

Figure 12a shows the mode at 178 Hz caused by driving a closed box with velocity at phase. This result can be obtained as the transducer on the front panel moves the panel outwards as the transducer on the rear panel moves the panel inward since the front and rear sides face each other. This can be achieved, for example, by electrically connecting the transducers to different phases using the switches shown in FIG. 6. 12B shows vibration at 1000 Hz.

13A and 13B show a box-like frequency mode, identical to a monopole with front and rear panels moving in reverse with electrical connections to the transducers in phase. As shown, a complex response is obtained again.

12C and 13C show the air pressure in the box driven at 1000 Hz with positive and single poles, respectively, according to the response of the boxes shown in FIGS. 12B and 13B. Figure 12b clearly shows an asymmetric response even though the drive and box are symmetrical. 13C shows very different pressure responses caused by driving the same box in different ways.

The transducer speed for a frequency graph obtained in a closed box is shown in FIG. 14. 14A and 14B show that, as expected, the response (driven by a single pole) at the front and back of the symmetrical sealed box is harmonized. 14C shows significantly less flat and therefore undesirable results with results obtained for positive drive of the same box.

Of course, all of the above results can lead to improvements in using the shell bent back on its own just to enclose the calculations or volume.

FIG. 15 shows a graph of the velocity response for a box driven by two transducers, one in front (FIG. 15A) and one in back (FIG. 15B), with stiffness different from the rear. As you can see, the response on the front is good, unlike the response on the back. Thus, by using asymmetric ones, it is often possible to increase the mode density well.

It should be noted that there is a difference between the devices as described in FIG. 5 with multiple planes and the devices as in FIG. 1 in the form of a continuous curve. The coupling 23 between the faces acts as a hinge so the resonant bending wave mode does not simply move from one face to the next. Rather, it leads to more complex combinations of modes.

Other multi-sided structures are also possible. 16 to 20 show cross-sectional views of various structures having the same shape as the truncated rectangular pyramid, tetrahedron, dodecahedron, cylinder and cone. For example, the cylinder shape may or may not have an end face and may or may not have a conical back face so that each shape may be open or closed. Each of the faces can be formed separately and joined, and a set of faces or even an entire structure can be formed collectively.

As mentioned in WO97 / 09842, the aspect ratios of isotropic rectangular panels are 0.707: 1 and 0.882: 1. It is also possible to optimize the acoustic device according to the invention in order to maximize the resonant mode in frequency by adjusting the properties of the shell and to provide a reasonable coupling of the transducer to the mode by accurately positioning the transducer in the panel.

This can be done using the techniques mentioned in the variously distributed mode patent applications. In particular, the method of finding the optimal aspect ratio and the use of the method of finding the transducer position in order to provide as good a result as possible is described in WO99 / 41939 (published in the name of New Transducers Ltd.).

In order to find the appropriate physical properties for the open box, the first step that has been performed is to variously model the aspect ratio of the center panel of the open box of FIG. 5. The aspect ratio varied from 1 to 2.25, and the mode-matched frequencies were calculated by finite element analysis. The mean square center deviation of the mode frequencies is shown for the aspect ratio (see FIG. 21). The median deviation of the mode frequencies is obtained by subtracting twice the frequency of the nth mode from the n + 1th mode plus the frequency of the n-1th mode for the nth mode. If the modes are equally spaced this value will be zero. Therefore, the mean square median deviation provides a picture with advantages for various aspect ratios. The smaller the mean squared mean, the better.

It can be seen from FIG. 21 that a preferable result is obtained between an aspect ratio of 1.6 and 2.2. Particularly preferred results are obtained with an aspect ratio between 1.95 and 2.05. An aspect ratio of 2 is taken as a useful value for future studies.

The next step is to find a drive point that is optimized for the face. Velocity response as a function of frequency is calculated for several drive point positions. 22 provides three examples at the center 22a, at the standard drive point 22b for the flatly distributed mode panel, and at the optimal drive point 22c. Standard deviations in these graphs are shown as a function of position in FIG. 23. The best results are with the smallest deviations that are black. It does not appear at the edges of the panels, indicating that they are bad drive points.

As can be seen by observing the figure, the optimum drive point occurs in four regions. The first area is about 30% of the distance along the long side and 30% of the distance along the short side, and the other three areas are found by reflecting the first area about the central axis of symmetry. It is an area of about 70% along the long axis and 30% along the short axis, 30% and 70% along each axis, and 70% and 70% along each axis. These positions occur about the center of the approximate 3/7 and 4/9 coordinates, expressed as ratios of distance along the side, and differ from the optimal driving point for a simple rectangle.

These positions have the potential for significant changes and a desirable result is obtained with positions reflected on them at positions between 14% and 42% of the long side and between 22% and 34% along the short side.

Although the above calculations were performed without considering the effects of air, it would be a good indicator of the proper aspect ratio and transducer position in a practical device. Of course, features such as coupling with air and slight anisotropy of the faces can shift the optimum aspect ratio and drive position slightly.

The embodiment described above relates to a loudspeaker, ie a device for converting electrical energy into sound. The methods of the present invention are equally applicable to microphones in which the generated acoustic energy is converted into electrical energy by the transducer.

Claims (16)

A substantially continuous outer shell for sustaining the flexure wave, the shell being bent to at least partially enclose the air volume to couple the flexure wave to the volume to provide a couple resonance mode; And And a transducer coupled to the shell to couple the electrical signal to the coupled mode, which in turn is coupled to the ambient sound. The method of claim 1, The resonance mode spans the shell. A substantially continuous shell surrounding the volume, the shell maintaining a plurality of resonant modes combining the shell and the enclosed volume, the resonant modes spanning the shell; And And a transducer coupled to the shell for coupling the electrical signal to the resonant mode and then in turn to ambient sound. The method of claim 1, wherein The transducer is an exciter for exciting a resonant mode for the acoustic device to act as a loudspeaker. The method of claim 1, wherein A sound device, characterized in that it has a port in the outer shell. The method of claim 5, And the port includes a duct extending from the outer shell into the volume. The method of claim 1, wherein And the outer shell comprises a plurality of faces. The method of claim 7, wherein Wherein each face has a natural resonant frequency and the natural resonant frequency has a different value. The method of claim 8, Wherein said different natural resonant frequencies are selected such that the lowest frequency resonant mode between 10 and 20 is present at the interleaved frequency. The method of claim 7, wherein The outer shell comprises a front face, wherein the front face has an aspect ratio of 1.6 to 2.2. The method according to claim 7 or 10, Wherein the outer shell comprises a rectangular front face and the transducer contacts the front face at a position between 14% and 42% at the edge along the long side and between 22% and 34% from the edge along the short side. The method according to any one of claims 7, 10 or 11, Said outer shell comprising opposing front and rear surfaces. In claim 12, A first transducer is provided at the front side and a second transducer is provided at the rear side. The method of claim 13, And the first and second transducers are mechanically coupled. The method of claim 12, An acoustic device, characterized in that one transducer is coupled to both the front and the rear. A substantially continuous outer shell that sustains the bending wave, the shell being bent to at least partially wrap the volume to couple the bending wave to the volume to provide a couple resonance mode; And in a method of driving an acoustic device comprising two transducers connected to the shell, Driving two transducers with a phase of a common electrical signal to drive a coupled mode of shell and volume in unipolar form, and Radiating acoustic energy from the coupled mode into the ambient air.