JP3488749B2 - Bone conduction microphone - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bone conduction microphone for converting an osteoconductive acoustic signal transmitted through human bone or skin into an electric signal.

[0002]

2. Description of the Related Art A bone conduction microphone is a human voice signal (hereinafter referred to as an acoustic signal) that passes through human bones and skin.
Is obtained from the human skin surface and ear canal, etc., and generally has a structure that is difficult to react to changes in air pressure and changes in particle velocity, so even in an environment with high external noise, a bone conduction microphone It has the feature that it can transmit only the human voice signal with.

In this type of bone conduction microphone,
As a method for electrically converting a mechanical acoustic signal, there have been conventionally used a piezoelectric type (see Japanese Utility Model Laid-Open No. SHO 55-146785), an electromagnetic type (see Japanese Patent Laid-Open No. 58-182397), and an electrodynamic type (Japanese Utility Model No. Sho 63- 173991), carbon type, optical type and the like are known.

Among these various conventional examples, for example, a piezoelectric bone conduction microphone is a piezoelectric case sandwiched by a mounting member 43 in a metal protective case 41 as shown in FIGS. 6 and 7. When the element 42 is arranged and applied to human skin, acoustic vibration vibrates the entire metal case 41 through the skin surface, and the piezoelectric element 42 sandwiched by the mounting members 43 has inertia. By using the force to hold its position, the applied acoustic vibration is converted into an electric signal.

[0005]

However, it is known that human muscles and skin are tissues having extremely low hardness, and acoustically, such tissues have very high mechanical impedance. Therefore, in the above-described conventional technology, the acoustic signal obtained from the bone conduction microphone emphasizes only a particularly low frequency component, and becomes a voice of another person when compared with an actual voice signal. There is.

That is, when the structure for converting an acoustic signal into an electric signal as described above is replaced with a substantially electric equivalent circuit, FIG.
In this FIG. 8, Z is human bone, muscle, fat and skin, and this Z is expressed by the formula Z = R + jωLω = 2πf (f is frequency), and when the frequency is low, DC resistance is The component R is the main component, only the low frequency components are emphasized, and as the frequency becomes higher, the value of L due to human bones, muscles, fat and skin becomes very large, so that Z rapidly increases.

Various proposals have been made in the past for solving such a problem, but it is inevitable that external noise will be introduced when the structure is complicated or the sensitivity is increased. The bone-conduction type microphone has a problem that it cannot sufficiently reproduce human voice while sufficiently blocking external noise.

Therefore, the object of the present invention is to provide a simple structure,
It is an object of the present invention to provide a bone conduction microphone that can reliably reproduce human voice while blocking external noise.

[0009]

In order to achieve the above object, a bone conduction type microphone adopted by the present invention has a case in which one end is substantially open and the other end is substantially closed, and the case. A vibrating body fixed to the open end side, an electric converter housed in a case, and partitioning the inside of the case near the electric converter, and a front chamber on the open end side of the electric converter, Comprising partition means forming a back chamber on the closed end side of the electric converter, and a communication part that communicates the front chamber and the back chamber, the vibration applied to the vibrating body is within the front chamber. The pressure is changed, and a part of the pressure change is supplied to the back chamber through the communication part, and as a result, the pressure change given to the electric converter is converted into an electric signal. It is characterized in that it has to be converted to.

In the above structure, the vibrating body has a hardness close to that of human skin in order to obtain mechanical impedance matching, and is made of a soft material such as silicon which can minimize the transmission loss of osteoconductive acoustic vibration. The rubber has a substantially U-shaped cross section, and the vibrating body has a substantially vibrating surface that is hard to prevent vibrations other than bone-conducting acoustic vibrations. The plate-shaped member may be provided, and an electret condenser microphone (ECM) can be cited as a preferable example of the electric converter.

Further, in the above structure, resistance means for the purpose of equalizing the pressure inside the front chamber and the back chamber and the outside pressure may be adopted, and the resistance means may be the front chamber and the back chamber. Examples thereof include pores that communicate the inside and the outside and a breathable material.

[0012]

In the bone-conduction type microphone of the present invention, when the microphone is applied to human skin or the like, the acoustic signal transmitted to the portion vibrates the vibrating body first, and then this vibration is generated in the case (mainly in the front chamber). ) The pressure change vibrates the vibrating body of the electric converter, and the vibration of the vibrating body is converted into an electric signal. That is, the acoustic signal on the human skin is not directly transmitted to the electric converter, but is first transmitted to the pressure change in the case and then transmitted to the electric converter. A part of the frequency change related to the frequency is transmitted to the back chamber through the communication hole, because the low frequency component is acoustically short-circuited by the communication hole, and as a result, the low frequency component is transmitted. It can be greatly attenuated.

Further, since the case is opened only at one end, the vibrating body is arranged at the open end, and the vibrating body is brought into contact with the skin or the like, external vibration is applied to the electric converter. There is no fear of being able to sufficiently block external noise.

[0014]

Embodiments of the present invention will be described in detail below with reference to FIGS. 1 to 6 of the accompanying drawings.

FIG. 1 is a longitudinal sectional view of an example 1 of the bone conduction type microphone according to the present invention, and FIG. 2 is a cross sectional view of the bone conduction type microphone. This bone conduction microphone 1
Is generally composed of a case 3, a vibrating body 5 fixed to the case 3, and an electric converter 7.
Open one end (left side of FIG. 1) and the other end (right side of FIG. 1)
Is formed into a closed cylindrical shape, and the vibrating body 5 is fixed to the open end thereof to seal the inside of the case 3.

The material for the case 3 is not particularly limited, but a material having a high hardness such as a metal material or a plastic material or a material having a vibration absorbing property is used. Thus, a material having a high hardness is used for the material of the case 3. As a result, it is possible to prevent the influence of external noise from other than the vibrating body 5, so that only the acoustic vibration from the vibrating body 5 side is transmitted to the case 3, and the present invention is provided near the speaker, for example. Even when the bone conduction microphone 1 of 1 is used, the howling phenomenon is less likely to occur.

The vibrating body 5 is brought into contact with human skin or the like,
An acoustic signal is converted into mechanical vibration through the skin, and the vibrating body 5 is preferably a soft material that can vibrate when it comes into contact with the skin, and in particular, a material having substantially the same hardness as human skin. For example, it is preferable to use a soft thin film material such as silicon rubber.

Further, in this embodiment, the vibrating body 5 has a shape in which its peripheral portion 5a, which is a joint portion with the case 3, is bent and easily vibrates, but in order to make it less susceptible to external noise. It is preferable that the bent peripheral portion 5a has a short length.

As shown in FIG. 1, a thin plate-shaped member 8 having high hardness is inserted into the soft thin film material of the vibrating body 5 so that the bone conduction microphone 1 of the present invention is temporarily cut into human skin or the like. Even if it is located away from the surface of (3), it is possible to prevent external noise from being directly converted into the pressure in the case 3. or,
The shape of the vibrating body 5 may be inserted into the ear canal, and a mechanical acoustic signal may be obtained from the ear canal.

An electric converter 7 is arranged in the case 3, and a partition wall 71 faces the vibrating body 5 on the open end side in a space formed by the case 3 and the vibrating body 5. It is divided into a chamber 9 and a back chamber 11 on the closed end side.

The electric converter 7 is not particularly limited as long as it can convert the pressure vibration of the front chamber 9 and the back chamber 11 into an electric signal, but it is expected to have a simple structure and cost reduction. It is preferable to use a general-purpose electret condenser microphone (ECM) that can be used and is excellent in picking up sound in a high frequency region, and a close-talking type or directional ECM is particularly preferable.

The front chamber 9 and the back chamber 11 are communicated with each other by a communication pipe 13. By thus communicating the front chamber 9 and the back chamber 11 with inertance, the pressure change in the front chamber 9 is changed. And the pressure change in the back chamber 11
Since pressure changes in the same phase are applied from the front and back surfaces of the electric converter 7, the result is as shown in FIG. 3 on the vibration plate of the electric converter 7, and the pressure change is out of phase.

That is, in the front chamber 9, since the electric converter 7 faces the vibrating body 5, the vibration of the vibrating body 5 is directly applied as a pressure change, while this vibration is generated in the communicating pipe 13 having inertance. It is transmitted and transmitted to the back chamber 11, and in the electric converter 7, as shown in FIG. 3, the pressure vibration is out of phase and is transmitted as vibration having exactly the opposite amplitude, so that the low frequency region is effectively attenuated. It can be done.

As described above, the communication pipe 13 functions as the inertance for damping in the low frequency region, but the communication portion in the present invention is not limited to such a pipe shape, for example, a slit shape. Also exhibits the same effect as the communication pipe.

The case 3 is further provided with a communicating body 23 for communicating the front chamber 9 and the back chamber 11 with the outside of the case 3, and the communicating body 23.
Is to convert the atmospheric pressures of the front chamber 9 and the back chamber 11 and the outside air to the equivalent while applying a constant resistance, and is configured to respond to changes in the atmospheric pressure of the outside air without introducing external noise.

In this embodiment, the communicating body 23 is a pipe in which the rear surface of the case is communicated with the front chamber 9, and the support pin 25 is inserted into the small hole 24. However, the communicating body 23 has a certain ventilation resistance. A breathable material such as non-woven fabric or sponge may be used as long as it can form fine pores. The position of the communicating body 23 is not particularly limited as long as it is within the case 3.

An example of the bone conduction microphone of the present invention constructed as described above converts an acoustic signal into an electrical signal as follows. First, an acoustic signal, which is a bone vibration that vibrates in response to a human voice, is transmitted to the vibrating body 5 through the skin or the like, and the vibration of the vibrating body 5 is not directly transmitted to the electric converter 7, 3 is converted into air vibration as a pressure change in the front chamber 9 in particular, and as a result, the pressure change is not attenuated, and the electric converter 7 is satisfactorily processed.
When an electret condenser microphone (ECM) is used for the electric converter 7, a high frequency pressure change is picked up with good sensitivity.

At this time, the pressure change in the front chamber 9 is also transmitted to the back chamber 11 via the communication pipe 13, but as shown in FIG. 3, the pressure change is transmitted with a phase shift, and the communication having inertance is established. In the pipe 13, when the pressure change is transmitted therethrough, the frequency in the low frequency region is attenuated.

As described above, by providing the front chamber 9 and the back chamber 11 and communicating with each other by the communication pipe 13, as shown by the solid line in FIG. 4, the frequency from the low frequency region to the high frequency region is substantially reduced. It is possible to pick up evenly, and as compared with the conventional example shown by the broken line in the figure, only the low frequency region is not noticeably picked up. It can be regenerated.

Moreover, since the external noise is surely shut out by the case 3, and the acoustic vibration is transmitted only through the vibrating body 5 in contact with the skin, it is hardly affected by the external noise.

Further, even when the air conditioner is used in a place higher by several tens of floors than the ground, since the pressure of the outside air is adjusted by the communicating body 23, it is affected by the change of the pressure outside the case in the high place. Never.

Here, the bone conduction microphone of the present embodiment will be described with an equivalent conversion circuit. FIG. 5 is a circuit diagram obtained by equivalently converting the configuration of the above-described embodiment into an electric circuit.
In, Z is human bone, muscle, skin and fat,
When a sound signal is converted into electric vibration, it acts as an electrically combined resistance and is a vibration source unit.

R1 and L1 are vibrators 5 in contact with the human skin surface, and the circuit including them is a mechanical circuit section.
When R1 and L1 are made of a soft material similar to human skin for the vibrating body 5, they are incorporated in the above-mentioned vibration source section in order to obtain mechanical alignment.

C1 is the pressure change in the front chamber, C2
Is a pressure change in the back chamber, and is shown as a capacitor in which each pressure change is converted into a change in capacitance. R2 is an atmospheric pressure equivalent resistance in the case, and the communicating body 23 is equivalently converted as an electric resistance. It was done.
L2 is an inertance for low frequency attenuation, and the communication pipe 13 obtains this acoustic inertance.

As is clear from the above equivalent circuit, the low-frequency attenuation inertance L2 by the communication pipe 13 is short-circuited in the low-frequency region, and the signal from the acoustic system to the mechanical system (including the ECM) is transmitted. Suppresses transmission,
It is possible to cut low frequency components.

[0041]

According to the bone conduction microphone of the present invention, a mechanical sound signal on human skin is transmitted as a pressure change to the front chamber and to the back chamber in different phases only through the vibrating body. , This pressure change is converted into an electric signal by the electric converter,
With a simple configuration, low frequency components can be greatly attenuated, and uniform frequency components can be obtained from the low frequency region to the high frequency region.

Further, since the vibration transmitted to the case is not directly taken out but the pressure change in the case is electrically converted, the external noise can be surely cut off.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a bone conduction microphone according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the bone conduction microphone shown in FIG.

FIG. 3 is a graph showing pressure changes in a front chamber and a back chamber.

FIG. 4 is a graph showing frequency characteristics of bone conduction microphones according to an example and a conventional example.

5 is an equivalent conversion electric circuit diagram of the bone conduction microphone shown in FIG.

FIG. 6 is a vertical cross-sectional view of an example of a conventional bone conduction microphone.

FIG. 7 is a cross-sectional view of an example of the bone conduction microphone shown in FIG.

8 is an equivalent conversion electric circuit diagram of an example of the conventional bone conduction microphone shown in FIGS. 6 and 7. FIG.

[Explanation of symbols]

1 Bone conduction microphone 3 cases 5 vibrating body 7 Acoustic transducer 71 partition 9 Front chamber 11 back chamber 13 Communication pipe

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Claims (9)

(57) [Claims] 1. A case having one end substantially opened and the other end substantially closed, a vibrating body fixed to the open end of the case, and an electric converter housed in the case. Partitioning means for partitioning the inside of the case near the electric converter, forming a front chamber on the open end side of the electric converter and a back chamber on the closed end side of the electric converter, the front chamber and the A communication section that communicates with the back chamber, the vibration applied to the vibrating body changes the pressure in the front chamber, and a part of the pressure change is supplied to the back chamber via the communication section. The bone conduction microphone is characterized in that the pressure change given to the electric converter is converted into an electric signal as a result. 2. The bone conduction microphone according to claim 1, wherein the vibrating body is made of a soft material that can vibrate due to bone conductive acoustic vibration. 3. The bone conduction microphone according to claim 2, wherein the vibrating body is made of silicon rubber. 4. The bone conduction microphone according to claim 1, wherein the vibrating body has a substantially U-shaped cross section. 5. The vibrating body is provided with a hard plate-shaped member on its substantially vibrating surface for preventing vibration due to vibrations other than osteoconductive acoustic vibrations. Item 5. The bone conduction microphone according to any one of Items 1 to 4. 6. The bone conduction microphone according to claim 1, wherein the electric converter is an electret condenser microphone. 7. The bone conduction microphone according to claim 1, further comprising an equalizing unit that equalizes the pressure inside the front chamber and the back chamber and the external pressure. 8. The bone conduction microphone according to claim 7, wherein the equivalent means is a pore that communicates the inside of the front chamber and the back chamber with the outside. 9. The bone conduction microphone according to claim 7, wherein the resistance means is a breathable material that communicates the inside of the front chamber and the back chamber with the outside.