JPS6362956B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ear microphone that transmits sound by electrically converting bone conduction sound signals from the wall of the external auditory canal.

Conventionally, as the vibration-electric conversion element used in this type of ear microphone, a rectangular piezoelectric element is used and the element is generally supported in a cantilevered state. Using the element alone was disadvantageous in terms of the sound quality of the audio output.

That is, this is because the frequency characteristics of sound generated in the mouth cannot sufficiently compensate for the attenuation frequency characteristics of the sound that is received while being transmitted to the external auditory canal by bone conduction. As shown in FIG. 1, the frequency characteristic a of voice attenuation decreases approximately linearly on a logarithmic scale as the frequency increases. Therefore, in order to bring the microphone closer to the sound generated from the mouth and increase the clarity, it is necessary to design a microphone that has the sensitivity to correct the frequency characteristic a within the required band (approximately 300 to 3300 Hz) as shown in b in Figure 1. is desired. However, in conventional microphones having a cantilever structure using piezoelectric elements, this frequency characteristic cannot be sufficiently corrected for the reasons described below.

In other words, the first reason is that in the cantilevered structure of the piezoelectric element, compensation is performed using the Q of the resonance point, but the Q is too high, causing overcompensation, and due to this overcompensation, two carrier frequencies are used. When configuring a two-way communication system, the housing must be raised, and in the case of a two-way communication system using a single carrier frequency with an automatic switching method that does not require manual transmission/reception switching, a voice-activated automatic switching device is required. There were drawbacks such as malfunctions. Therefore, if the holding portion of the piezoelectric element is supported by a buffer in order to reduce the Q, practical control of the Q becomes difficult, resulting in a significant drop in the output level.

The second reason is that the cantilevered structure using a piezoelectric element exhibits flat frequency characteristics in the low range as shown in a in Figure 2. The disadvantage is that the image is emphasized and the clarity is reduced as shown in b in the figure. Therefore, in order to prevent this harmful effect, it is necessary to further insert a high-pass filter into the external electrical circuit to improve the clarity.
As a result, the disadvantage was that the circuit configuration was complicated and the cost was high.

The present invention aims to correct the above-mentioned drawbacks, and its purpose is to provide a high-output system that can faithfully compensate for the necessary frequency characteristics without overcompensating, and also eliminates the need for an external low-frequency improvement filter. The goal is to provide high-clarity ear microphones.

Next, one embodiment of the present invention will be described with reference to FIG. 3 and subsequent figures.

Reference numeral 1 denotes an insert made of a large material such as zinc die-casting, which is inserted into the ear canal of a listener, and whose outer periphery is covered with a plastic coating 2. The insert body 1 is formed with a through hole 1a and an insertion hole 1b. Reference numeral 3 denotes a sound conduit inserted into the through hole 1a of the insert 1 while being supported by a ring-shaped damper 4 made of an elastic material such as rubber, and is constituted by a metal pipe with a large mass. One end of this sound conduit 3 is opened at the front end of the insert body 1. Reference numeral 5 denotes a vibratory electric transducer using an electret, which will be described later. 6
is an elastic member made of natural or synthetic rubber that covers the rear part of the insert 1, and a cavity 6a is formed in the center. Reference numeral 7 denotes an outer body made of the same material as the above-mentioned insert body 1 that covers the outer periphery of the above-mentioned elastic member 6, and has a hole 7a formed in the same plane as the sound pipe 3 and the conversion element 5. A bushing 8 is fitted onto 7a. A metal pipe 9 is fitted into the bush 8, and the metal pipe 9 and the sound pipe 3 are connected by a tube 10. 1
Reference numeral 1 denotes an externally led rubber pipe fitted into the bush 8 and connected to a metal pipe 9, into which a lead wire 5a from the conversion element 5 is inserted through a hole in the metal pipe 8. 12 is a plastic sheath that covers the outer periphery of the outer body 7.

Although not shown, the rubber pipe 11 is connected to a speaker in the receiver, and is also connected to a lead wire 5.
a is connected to the transmitter.

Next, the principle of operation of the electret conversion element 5 will be explained with reference to FIGS. 4 and 5.

The electret conversion element 5 applies a voltage between opposing electrodes (fixed electrode and movable electrode), and when the movable electrode is displaced, Q = CV in proportion to the amount of displacement.
The output voltage obtained is as follows. However, since the output voltage from this electret conversion element 5 has a very high impedance, in the present invention, an impedance conversion element (FET) is connected as shown in FIG. 5 to reduce the impedance.

Thus, the electret conversion element 5 according to the present invention
In this case, a fixed electrode, a movable electrode, and an FET as an impedance conversion element are inserted into the insertion hole 1b shown in FIG. 3.

Next, a specific example of the electret conversion element 5 shown in FIGS. 6 and 7 will be explained.

5a is a shield case consisting of a large diameter part and a small diameter part, 5b is a damper made of rubber or the like fixed to a part of the large diameter part close to the small diameter part via a damper holder 5c, and 5d is pivotally supported by the damper 5b. A movable electrode made of a metal rod, one end of which is a shield case 5a.
The other end extends to the distal end of the small diameter portion, and the other end extends to the proximal end of the large diameter portion. A damper 5b is attached to this movable electrode 5d.
A lead wire 5e is connected to the portion pivotally supported by. 5f is a flat fixed electrode fixed to the large diameter portion of the shield case 5a, and a lead wire 5g is also connected to this fixed electrode 5f. 5h is a FET to which an FET not shown is attached.
On the mount, the lead wire 5e is connected to the source of the FET, and the lead wire 5g is connected to the gate of the FET. The output signal of the FET is sent to an external transmitter through the FET output lead 5i.

By the way, in the above structure, the output level can be adjusted by the length and shape of the movable electrode 5d, the distribution ratio depending on the position of the damper 5b, and the frequency characteristics can be determined by the elastic coefficient of the damper 5b, the weight of the movable electrode 5d, etc. . Therefore, as an example to obtain an output level and frequency characteristics that do not cause any practical problems, a hollow aluminum pipe with a diameter of 1 mm and a length of 8 mm is used for the movable electrode 5d, and butyl rubber with a high resistance is used for the damper 5b. For example, an ear microphone with characteristics as shown in FIG. 8 can be obtained.

Next, to explain the operation, the inserter 1 is inserted into the user's ear canal, and when the user speaks, the bone conduction sound signal from the ear canal wall is transmitted to the inserter 1 and then to the conversion element 5. The signal is converted into an electrical signal, sent to the transmitter via the lead wire 5i, and radiated from the antenna as a radio wave.

Since the conversion element 5 is an electret, the output frequency characteristics are optimally compensated and converted to low impedance by the FET.
In addition, external vibrations such as friction noise generated between the pipe 11 and clothing transmitted from the outside through the pipe 11
1 and the mass of the outer body 7, and further the lead wire 5i, the damper 4, and the tube 10
The vibration is absorbed by a vibration system made up of the spring elasticity of the elastic member 6 and the mass of the insert 1. Vibrations caused by hair contact noise or wind noise that are directly applied to the outer body 7,
The vibration is absorbed by a vibration system made of the mass of the insert 1 and the spring elasticity of the elastic member 6, lead wire 5i, damper 4, and tube 10.

In any of the above cases, it is desirable that the resonance frequency of each resonance system falls outside the low range of the effective sensitivity frequency band (for example, 300 to 3300 Hz) of the conversion element 5. For this purpose, the weight of the insert body 1 and the outer body 7 must be large, and the elastic modulus of the elastic member 6 must be large. In particular, when the elastic modulus of the elastic member 6 is large, the effective load weight of the transducer element 5 against external auditory canal sound vibrations is approximately only the insert body 1, and the weight of the outer body 7 has almost no effect, thereby avoiding a decrease in the audio signal output. It will be done.

On the other hand, the external signal received by the receiver is converted into sound by the speaker, guided to the sound pipe 3 via the pipe 11, metal pipe 9, and tube 10, and emitted into the ear canal.

Here, the sound pipe 3 vibrates due to the vibration energy of the sound passing through the sound pipe 3, but it does not respond to vibrations with a frequency higher than the resonance frequency determined by the elasticity of the damper 4 and the mass of the sound pipe 3. The sound is absorbed by the vibrations of the sound pipe 3 and transmitted to the outside of the damper 4 in a damped manner. Furthermore, the vibration energy of the sound passing through the sound pipe 3 is transferred to the pipe 11, the bush 8, the outer body 7, the elastic body 6, and the insert body 1.
However, it is absorbed by the elasticity of the elastic body 6 and the mass of the insert body 1. Note that the above-mentioned resonance frequency is also desirably outside the low range of the effective sensitivity frequency band of the conversion element 5. For this purpose, it is desirable that the mass of the sound pipe 3 is large and that the damper 4 has a large elastic coefficient. Therefore, in this example,
The voice-activated automatic switching device operates reliably to enable two-way communication using a single carrier frequency, even without using a switch to switch between transmission and reception.

In the above-described embodiment, the sound from the external speaker is guided into the external auditory canal through the sound conduit 3, but the speaker may be installed inside the insert 1. In addition, in the embodiment, the shield case 5
Although the conversion element 5 is shown as being attached inside the insert 1, if the insert 1 has a shielding effect, it may be attached directly inside the insertion hole 1b of the insert 1.

As described above, the present invention has an electret-based vibration-electric transducer mounted inside the insert inserted into the ear canal, thereby making it possible to faithfully compensate for the necessary frequency characteristics without overcompensating. This allows the user to hear clear audio, and since there is no need to provide a filter for improving low frequencies as in the conventional case, it has the advantage that it is possible to obtain an inexpensive product.

[Brief explanation of drawings]

Figure 1 is a diagram showing the frequency characteristics in the ear canal, Figure 2 is a diagram showing the frequency characteristics in the ear canal.
The figure shows the frequency characteristics when using a piezoelectric conversion element, Figure 3 is a cross-sectional view of the ear microphone according to the present invention, and Figures 4 and 5 are equivalent circuit diagrams when an electret is used as the conversion element. , FIG. 6 is a cross-sectional view of the electret conversion element, FIG. 7 is a cross-sectional view taken along the line shown above, and FIG. 8 is a diagram showing the frequency characteristics of the ear microphone according to the present invention. 1... Insert body, 5... Electret conversion element, 5a... Shield case, 5b... Damper,
5d...Movable electrode, 5f...Fixed electrode.

Claims (1)

[Claims] 1. An insert body 1 made of a material with a large mass such as zinc die-casting, and having a portion that can be inserted into the ear canal of a listener and having an insertion hole 1b formed from the back side to the front side, and the above-mentioned parts of the insert body 1. Insertion hole 1b
An electret conversion element 5 includes a movable electrode 5d which is mounted so as to be able to vibrate through a damper 5b, and a fixed electrode 5f which is fixed oppositely to one end of the movable electrode 5d. An ear microphone characterized in that it is equipped with an impedance conversion element such as a FET that is connected to achieve low impedance.