JPS62295096A - Acoustic lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Technical Field 1] The present invention is an acoustic lens, and more specifically, a sound that converges sound waves in a predetermined frequency band! 5 lenses.

[Background technology] In recent years, traffic noise generated when vehicles pass along railway lines and roads has become a problem, and countermeasures such as installing soundproof walls have been taken, but since sound waves are diffracted, In addition, with the mechanization of office processing (OA), computers, word processors, and other devices are increasingly used in offices, and dot impact printers are often used as output devices. has been done. Such dot impact printers make a lot of noise when in operation, and since the diffraction of sound waves cannot be prevented by partition walls or the like, deterioration of the office environment due to the noise has become a problem. Furthermore, noise sources such as the sound of the fan of the air conditioner and the sound of the motor are noise sources, and since the air inlet and outlet of the air conditioner cannot be closed and surrounded by walls, sound insulation cannot be achieved. As described above, the conventional sound insulation devices provided upstream do not take sufficient consideration to the diffraction of sound waves, and in that sense, the sound insulation effect cannot be said to be sufficient.

On the other hand, devices are being considered that allow sound waves to pass through while converging them. That is, as shown in FIG. 14, a combination of a plurality of inclined plates 2 is provided, and as shown in FIG. 15, a combination of a plurality of obstacles 3 is provided. Set up multiple routes within the
The difference in path length is used to converge the sound waves. In this device, since the path length is related to the wavelength to be converged, the convergence frequency band is narrow, and there is a problem in that the device as a whole needs to be large in order to converge sound waves in the low frequency range. Another problem is that it cannot be applied to sound sources that require a large aperture ratio (such as when ventilation is required for air conditioning, etc.).

[Objective of the Invention 1 The present invention has been made in view of the above-mentioned points, and its main purpose is to converge sound waves only at a specific point, thereby emitting sound only at a specific location. The objective is to provide an acoustic lens that allows sound waves to be heard and avoids the propagation of sound waves to unnecessary locations.Another objective is to provide an acoustic lens that allows a relatively large aperture ratio. There is a particular thing.

[Disclosure of the Invention 1 (Structure) The acoustic lens according to the present invention uses a straight hollow tube thinly formed of a viscoelastic material as a control element for controlling the phase velocity of a sound wave, and includes a plurality of control elements. are arranged so that their axial directions are substantially parallel to each other, and other control elements are arranged on a concentric circumference centered on one control element in a plane perpendicular to the axial direction of the control element. The closer the control element is to the control element, the smaller the phase velocity of the passing sound wave is set, and this configuration allows for a relatively large aperture ratio and converges the sound waves to prevent them from propagating to unnecessary locations. .

(Basic Principle) First, the basic principle of the present invention will be explained. In the following explanation,
As shown in FIG. 8, a straight hollow cylindrical body is used as the control element 1, but the present invention is not limited to a cylindrical body, and may be a cylinder having another cross-sectional shape. Such control element 1
When a sound wave passes through the tube, the tube wall of the control element 1 vibrates as shown by the arrow in FIG. However, for a unit length portion of a hollow body with both ends open, fjS9
It can be thought of as an equivalent electrical circuit as shown in the figure. That is, the inertance La of the gas inside the tube, the acoustic capacitance Ca of the gas inside the tube, Ir! wall inertance Lw
, the compliance Cm of the tube wall, and the conductance Gw of the tube wall determine the acoustic characteristics of the unit length of the control element 1. The inner radius of the tube is r, and the wall thickness of the tube is L1.
The inner surface area per unit length of the tube is 81 The mass per unit length of the tube is m (=2πrρwt: ρ is the density of the tube wall)
, the Young's modulus of the tube wall is E, the proportional constant of the tube wall conductance is ) and ti, each parameter is expressed by the following formula.

La=P/S Ca=S/K Lw=m/4 π2r" Cw=2 x r3/E t Gw= ω Therefore, the resonant frequency fr of the control element 1 is expressed by the following equation 7% Equivalent electrical direction path mentioned above If an equivalent conductance Geq and an equivalent capacitance Ceq expressed by the following equations are introduced into , the equivalent electric circuit of FIG. 9 can be further replaced with the equivalent electric circuit of FIG. 10.

Geq=Gw/((1al 2Lwcw)2+ω2Gw
"Lw") If the phase constant β of the equivalent electric circuit shown in FIG. 10 is determined, the phase constant of the sound wave passing through the tube has been determined, and the phase velocity Vp can be defined from the phase constant β.

+ω2LaCeq)”)’l/p=ω/β As is clear from the above equation, the equivalent Funguktance G
Since eq and equivalent capacitance Ceq have a singular point at the resonance frequency, as shown in the fIS11 diagram,
The phase velocity Vp changes greatly near the resonance frequency. Furthermore, since the phase velocity Vp is calculated for a unit length, it is clear that it is a function of the length of the control element 1, and furthermore, the density of the tube wall, Young's modulus, and inner diameter are included in the phase constant β. , so we can see that it is a function of them. FIG. 12 shows the experimental results of the frequency characteristics of the phase velocity for this control element 1.

In this way, it can be seen that the phase velocity changes significantly at a specific frequency. Here, the measuring device includes a speaker 11 that sends out sound waves from one end of the control element 1 into the control element 1, and a speaker 11 that is inserted into the control element 1 and transmits sound waves at one place inside the control element 1, as shown in Figure @i3. a probe microphone 12 that picks up sound;
A signal generation circuit 13 and an amplifier circuit 14 that generate electric signals input to the speaker 11, a measurement amplifier circuit 15 that amplifies the sound picked up by the probe microphone 12, and a measurement amplifier ji315 that adjust the phase of the sound output from the measurement amplifier ji315. It is composed of a phase meter 16 for detection, and an arithmetic control device 17 that controls the frequency of the signal output from the signal generation circuit 13, records the output of the phase meter 16, and calculates the phase velocity within the control element 1. . Here, the arithmetic and control device 17 is configured using a microcomputer or the like. The control element 1 has a Young's modulus of 7 and OX 10'[N/R21
(measured by a complex elastic modulus measuring device, that is, a viscoelastic spectrometer), and the density is 1190 [*y/z3
The inner diameter was set to 25xx, and the thickness of the tube wall was set to 0.3u.

By using the above-mentioned characteristics, there will be a difference between the phase velocity within the control element 1 and the phase velocity outside the control element 1, so by using this control element 1, the sound wave can be made to bend 47r. be. In the following embodiments, a plurality of the above-mentioned cylindrical control elements 1 are used to converge sound waves.

(Example 1) As shown in FIGS. 1 and 2, a plurality of control W elements 1
are arranged with their axial directions parallel to each other, and one end surface of the control element 1 is disposed on the same plane A in a plane perpendicular to the axial direction of the control element 1. Each control element 1 is arranged on a plurality of concentric circles with one control element 1a as the center and other control elements 1 having different radii in a plane perpendicular to the axial direction of the control element 1. The control elements 1 on each circumference are set to have equal pipe lengths, and the pipe lengths are set to become shorter as the distance from the central control element 1a increases.

As mentioned above, the control element 1 delays the phase velocity inside the tube compared to the phase velocity outside the tube below the resonance frequency, so the longer the tube length, the greater the phase delay, as shown in Figure 2. , the wavefront W s i that was introduced into the control element 1 and was orthogonal to the axial direction of the control element 1 becomes on xVcIfA of the central axis of the control element 1a, which is the center after passing through the control element 1. In other words, the wavefront Wso of the sound wave that has passed through each control element 1 is inclined with respect to the central axis as shown in Fig. 2.Here, if the control element 1 is formed of the material used in the experiment, , the pipe length of control I element 1 is 200zx, the separation between adjacent control elements 1 is 5xm,
When the difference in pipe length between adjacent control elements 1 is 50 av,
The phase velocity of the 500 Hz sound wave in the tube was 100 z/s, and the convergence point of the sound wave was a point 3521 in front of the control element 1a, which was the center.

(Example 2) In this example, the density or Young's modulus of the tube wall is different.
By arranging the B element 1 on a plurality of concentric circles having different radii around one control element 1a in a plane orthogonal to the axial direction of the control element 1,
As in the first embodiment, the sound waves are converged. That is, as shown in FIG. 3, the axial lengths of the aE control elements 1 are set to be the same length, and only the density or Young's modulus of the tube wall is changed. For example, when changing only the density while keeping the Young's modulus constant, the density is set smaller as the distance from the central control element 1a increases.1. Conversely, when changing only the Young's modulus while keeping the density constant, the Young's modulus is set to be larger as the distance from the central control element 1a increases. Here, the control elements 1 on the same circumference have the same density or Young's modulus.

The phase velocity within the control element 1 becomes smaller as the tube wall density increases, as shown in FIG. 4, and becomes smaller as the Young's modulus becomes smaller, as shown in FIG. Therefore, in the above configuration, the wavefront, which was orthogonal to the axial direction of the control element 1 before being incident on the control I element 1, becomes on the central axis of the control element 1a, which is the center, after passing through the control element 1. It will converge.

Here, the control element 1 used in the measurement of fpJ4 and FIG.
, 6X106N/waterfall 2, and in FIG. 5, the density of the tube wall material was 1110 kg/z''.

As described above, while changing the density and Young's modulus of the tube wall material of the control element 1, control 1! !
By changing the length of element 1, the sound waves can be converged more efficiently.

(Example 3) In this example, the phase velocity within the control element 1 is controlled by using control elements 1 having different inner diameters. That is, the larger the inner diameter of the control element 1 is, the smaller the phase velocity is, so as shown in FIG.
By arranging the control elements 1 whose inner diameters become smaller as the distance from the central control element 1a increases, the sound waves are converged on an extension of the central axis of the central control element 1a. When the phase velocity is actually measured by changing the inner diameter of the control element 1, the results shown in FIG. 7 are obtained. Here, the wall thickness of the tube wall was 0°16 cm, the Young's modulus was 4.6×10'N/II2, and the density was 1110 kg/x.

Of course, if this embodiment is combined with the configurations of the first and second embodiments, it is possible to converge sound waves even more efficiently.

In each of the above embodiments, the phase velocity is controlled at frequencies below the resonance frequency where the phase velocity changes rapidly, so by setting the resonance frequency to a high frequency, the convergable frequency band can be expanded. Can be done. In addition, in the high frequency region even above the resonance frequency, there is an overhead where the phase velocity decreases depending on the Young's modulus and density of the tube wall, or the inner diameter of the tube. If used, it is possible to refract sound waves other than at low frequencies.

[Effects of the Invention] As described above, the present invention uses a thin straight hollow tube made of a viscoelastic material as a control element for controlling the phase velocity of a sound wave, and connects a plurality of control elements to each other. The control elements are arranged so that their axial directions are substantially parallel, and one control a! The pond control elements are arranged on a concentric circle centered on the l element °, and the closer the control element is to the center, the smaller the phase velocity of the passing sound wave is set, so the sound waves can be converged, and as a result, unnecessary This has the advantage of preventing sound waves from propagating in certain directions, and allowing sound waves to propagate only in the necessary directions. Furthermore, since the control element is made of a viscoelastic material and is formed into a thin straight tube shape, it has the advantage of good air permeability.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of Embodiment 1 of the present invention, FIG. 2 is a side view of the same as above, and FIG. 3 is a schematic configuration diagram of Embodiment 2 of the present invention.
4 and 5 are explanatory diagrams of the same operation as above, FIG. 6 is a schematic configuration diagram of Embodiment 3 of the present invention, and FIG. 7 is an explanatory diagram of the same operation as above,
Fig. 8 is a perspective view showing a control element used in the present invention, Figs. 9 and 10 are equivalent electric circuit diagrams of the control element, Figs. 11 and 12 are explanatory diagrams of the same operation as above, and Fig. FIG. 14 is a perspective view showing a conventional propagation direction control device, and FIG. 15 is an explanatory diagram of the same operation. 1 is the control element, 1a is the central control! l element. Agent Patent Attorney Ishi 1) Chief 7 Figure 3 Figure 6 Figure 9 Figure 1 O Figure 11 Kudanro (Hzl Figure 13)

Claims (5)

[Claims] (1) A straight hollow tube made of a thin-walled viscoelastic material is used as a control element for controlling the phase velocity of a sound wave,
A plurality of control elements are arranged so that their axial directions are substantially parallel to each other, and other control elements are arranged on concentric circles around one control element in a plane perpendicular to the axial direction of the control elements. An acoustic lens characterized in that the closer the control element is to the center, the smaller the phase velocity of the passing sound wave is set. (2) In a plane perpendicular to the axial direction of the control element, the axial length of each control element is sequentially shortened as it moves away from the central control element, and the axial length of each control element on the same circumference is The acoustic lens according to claim 1, characterized in that the lengths are set to be equal. (3) In a plane orthogonal to the axial direction of the control element, the inner diameter of each control element is made smaller as it moves away from the central control element, and the inner diameter of each control element on the same circumference is set equal. Claim 1 characterized in that
The acoustic lens according to item 1 or 2. (4) In a plane perpendicular to the axial direction of the control element, the density of the material forming each control element is gradually reduced as it moves away from the central control element, and each control element on the same circumference is made of the same material. The acoustic lens according to claim 1, 2, or 3, characterized in that the acoustic lens is formed by forming an acoustic lens. (5) In a plane perpendicular to the axial direction of the control element, the Young's modulus of the material forming each control element is increased one after another as it moves away from the central control element, and the control elements on the same circumference are made of the same material. The acoustic lens according to claim 1, 2, 3, or 4, characterized in that the acoustic lens is formed by forming an acoustic lens.