JP3288513B2 - Sound absorber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound absorber, and more particularly, to a sound absorber utilizing a resonance phenomenon which is suitably used for a partition having a soundproof function and a wall material.

[0002]

2. Description of the Related Art Conventional sound absorbers include rock wool, glass wool, rubber, porous polymer materials, porous ceramic materials and the like, and are widely used as sound insulation materials. The sound absorbing mechanism of these sound absorbers absorbs the energy of sound waves as vibration energy and converts it into heat energy by internal friction.

Further, as a sound absorbing material having a different idea from the above sound absorbing material, Japanese Patent Publication No. 3-44308 discloses a sound absorbing material using a mixture of a piezoelectric powder material and a polymer resin material. . According to the sound absorbing material of the publication, the energy of sound waves is not only simply absorbed by the sound absorbing material as vibrational energy, but also absorbed by the piezoelectric powder material and converted into electric charges. Leaks from the leakage path existing in the surroundings or in the piezoelectric powder material itself and is dissipated as heat, so that the sound absorbing properties of the sound absorbing material are improved.

[0004]

However, the above-described sound absorber has a large sound absorption coefficient at a high frequency, but has a low sound absorption coefficient for a low-frequency sound wave, and thus has almost no role as a sound absorber. is there.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a sound absorber having a large sound absorption coefficient even at a low frequency and capable of freely setting the sound absorption frequency.

[0006]

That is, according to the sound absorbing body of the present invention, a substantially sheet-like sound resonator having a certain outer periphery is provided.
The frame is provided in the inner space of the frame that provides a frame-shaped inner space larger than the outer circumference of the resonator, and is supported by the frame via an elastic body at an outer peripheral portion thereof. . Preferably, the resonator is an electromechanical transducer supported by the frame via the elastic body such as a spring, and the resonator has a mechanical loss tangent of 1 × 10 ⁻³ or more.
In particular, if a resonator is formed by a composite of an electromechanical transducer and a member having a mechanical loss tangent of 1 × 10 ⁻³ or more, vibration energy is converted into both heat energy and electric energy, resulting in high sound absorption. Rate is obtained. As the electromechanical transducer, a polymer piezoelectric element or a composite piezoelectric element made of a mixture of a piezoelectric powder material and a polymer material is preferably used. It is also preferable to fill a viscous material between the frame and the resonator.

[0007]

When a sound wave having the same frequency as the resonance frequency of the resonator is incident on the sound absorber of the present invention having the above-described structure, the resonator resonates and converts the energy of the sound wave into vibration energy most efficiently. By using a material having a large mechanical loss for the resonator, vibration energy is efficiently converted to heat energy. In particular, if a complex composed of a member having a large mechanical loss and an electromechanical transducer is used as the resonator, vibration energy is converted into both heat energy and electric energy, and a sound absorber having a high sound absorption coefficient can be obtained. Furthermore, if a viscous body is filled between the frame and the resonator, vibration energy is converted to thermal energy by friction generated between the resonator and the resonator.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the sound absorber of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of the vibration damping material of the present invention according to a preferred embodiment, and FIG. 2 is a side view of the resonator of FIG.

Referring to FIG. 1 and FIG.
In the figure, the resonator 3 is disposed in the internal space of the frame 1, and the resonator 3 is supported by the frame 1 via the spring 2. Here, assuming that the mass of the resonator 3 is m and the spring constant of the spring 2 is k, and the mass of the spring is negligible compared to the mass of the resonator, the resonance frequency fr of the resonator 3 is expressed by the following equation. You.

[0010]

## EQU1 ## fr = (4 k / m) ^1/2 / (2π)

The above equation shows the resonance frequency fr when no damping force acts on the resonator 3, but actually, damping force such as frictional heat of the spring and internal friction of the resonator acts. Assuming that the viscous damping coefficient representing this damping force is c, the resonance frequency f _R when the damping force works Is represented by the following equation.

[0012]

F _R = (4π ² fr ² -2γ ² ) ^1/2 / (2π); γ = c / (2m)

When a sound wave having a frequency coincident with the resonance frequency f _R is incident on the resonator 3, the resonator resonates, and the energy of the sound is converted to vibration energy most efficiently. Further, the energy of the co-oscillation is attenuated by various damping forces belonging to the resonator, thereby achieving sound absorption.
Therefore, it can be said that the sound absorption coefficient of the sound absorber of the present invention is governed by the above-described damping force inherent to the resonator. A high and preferable sound absorption coefficient can be obtained by using a resonator whose mechanical loss tangent is 1 × 10 ⁻³ or more. The mechanical loss tangent referred to in the present invention is a damping force acting due to internal friction of an object, and the viscous damping coefficient c is a general concept of the mechanical loss tangent.

As shown in FIG. 2, the resonator 3 has electromechanical transducers 4 (+5,
5) is a composite body obtained by laminating 5), which is one preferable embodiment for increasing the above-mentioned damping force. This is because when the resonator 3 vibrates, the electromechanical transducer also vibrates together with the vibrator 6, and the electromechanical transducer converts vibration energy into electrical energy. At this time, if the electrodes 5 and 5 of the electromechanical transducer are electrically connected via an appropriate resistor, the electric energy is consumed as Joule heat.
Therefore, the vibration energy is converted into both heat energy by the vibrating body 6 and electric energy by the electromechanical conversion element, and a high sound absorption coefficient is achieved.

As the electromechanical transducer of the present invention, a piezoelectric element, an electrostrictive element, an electret, or the like is used. A polymer piezoelectric element represented by polyvinylidene fluoride (PVDF) can easily have a large area. It is particularly suitable because it is resistant to impact and the material itself has a large mechanical loss tangent. Further, a composite piezoelectric element obtained by mixing fine particles of a piezoelectric ceramic represented by lead zirconate titanate (PZT) or barium titanate with a polymer material is also preferably used as the electromechanical transducer. In the case where a piezoelectric element is used, a part of electric energy is consumed as heat due to piezoelectric loss even if the electrodes are not connected by a resistor.

The sound absorber according to the present invention acts effectively on sound waves in a narrow frequency band before and after the resonance frequency of the resonator installed in the inner space of the frame, but a plurality of resonators having different resonance frequencies are used. If installed in parallel, it is possible to absorb sound over a wide frequency range.

When a viscous body is filled between the frame and the resonator, friction occurs between the resonator and the viscous body, so that vibration energy is converted to heat energy, and sound absorption is more effectively achieved. . Further, if the low frequency region of the sound wave is absorbed by the sound absorbing body of the present invention, and the high frequency region is absorbed by another sound absorbing material such as glass wool, sound absorption over the entire audible frequency range becomes possible. If a decorative plate or the like is attached to the frame, it can be used as a partition, a wall material, or the like.

[0018]

As described above, according to the present invention, a sound absorber having a large sound absorbing effect and an excellent sound absorbing performance especially at a low frequency can be obtained simply by installing a resonator corresponding to the frequency of the target sound wave. Obtainable.

[Brief description of the drawings]

FIG. 1 is a plan view of an anti-vibration material according to a preferred embodiment of the present invention.

FIG. 2 is a side view of the resonator shown in FIG. 1;

[Explanation of symbols]

 1: Frame 2: Spring (elastic body) 3: Resonator 4 (+5, 5): Electromechanical transducer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-166396 (JP, A) JP-A-57-124398 (JP, A) JP-A-5-347534 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G10K 11/16 E04B 1/99 H04R 17/10

Claims (6)

(57) [Claims] 1. A substantially sheet-shaped sound wave resonator having a certain outer periphery is disposed in an inner space of a frame body that provides a frame-shaped inner space larger than the outer periphery of the resonance body. A sound absorber is supported by the frame via a hole. 2. The sound absorber according to claim 1, wherein the resonator is an electromechanical transducer. 3. A resonator comprising an electromechanical transducer and 1.times.10.sup.- ^3.
The sound absorber according to claim 1, wherein the sound absorber is a composite with a member having the above-described mechanical loss tangent. 4. The sound absorber according to claim 1, wherein a mechanical loss tangent of the resonator is 1 × 10 ⁻³ or more. 5. The sound absorber according to claim 2, wherein the electromechanical transducer is a polymer piezoelectric element. 6. The sound absorber according to claim 2, wherein the electromechanical transducer is a composite piezoelectric element made of a mixture of a piezoelectric powder material and a polymer material.