JP5579120B2 - Throat microphone - Google Patents

Description

  The present invention relates to a throat microphone that can increase the intelligibility of an audio signal to be electroacoustic converted by making the frequency response adjustable according to environmental conditions.

  When a general microphone that picks up sound that propagates in the air and converts it into an electrical signal is used in an environment with a high noise level, such as an aircraft maintenance station, the necessary sound is drowned out by noise. The necessary voice cannot be picked up. In addition, even if an attempt is made to pick up sound generated by a diver underwater with a microphone, the sound cannot be picked up with a general microphone. Therefore, a magnet-type or electret condenser-type throat microphone that detects vibration of the throat when a person utters a voice is used so that the voice uttered by the person can be converted into an electrical signal even in the above environment. It is done. However, since such a throat microphone detects only the vibration of the throat, it cannot collect the frictional sound and the plosive sound generated at the mouth, and the intelligibility of the audio signal is inferior.

  Since the frictional sound and plosive sound contain a lot of relatively high frequency components in the audio signal, it is preferable to design the throat microphone so that the sensitivity in this frequency band is high. Therefore, it has been proposed to use a microphone using bone conduction sound as a throat microphone. A piezoelectric element that is robust and has a high output level is used as an electroacoustic transducer of a microphone that uses bone conduction sound. When a piezoelectric element is used as the electroacoustic transducer of the throat microphone, a bimorph type piezoelectric element (hereinafter referred to as “piezoelectric bimorph”) having a structure in which two piezoelectric elements are bonded together is used.

  Non-Patent Document 1 describes an example of a bone conduction microphone using a piezoelectric bimorph. Although a single piezoelectric bimorph can obtain high sensitivity near the resonance frequency, there is a problem that a region where high sensitivity can be obtained is narrow. Therefore, the bone conduction microphone described in Non-Patent Document 1 enables sensitivity correction in a wide frequency band by using a plurality of piezoelectric bimorphs. In the specific example of the bone conduction microphone described in Non-Patent Document 1, one end portions of three piezoelectric bimorphs are laminated with a conductive washer interposed therebetween, and the shaft is penetrated to be integrally fastened. Signals are output from the electrodes at both ends in the stacking direction. Therefore, three piezoelectric bimorphs are connected in series. The three piezoelectric bimorphs have different resonance frequencies due to differences in length, weights, and the like.

  According to the example of the bone conduction microphone described in Non-Patent Document 1, in the frequency band of 1 to 4 kHz, it is possible to obtain characteristics close to air conduction sound, that is, normal speech propagating through air, and the speech recognition rate is increased. Has been.

  According to the example of the bone conduction microphone described in Non-Patent Document 1, when the frequency band and the frequency response are adjusted, the weight of the weight fixed to each piezoelectric bimorph is changed to change the resonance frequency. difficult. Therefore, Non-Patent Document 1 does not disclose or suggest the electrical adjustment of the resonance frequency of each piezoelectric bimorph.

  A microphone using a piezoelectric bimorph, like an elastically controlled microphone such as an omnidirectional condenser microphone, has a constant output level in a frequency band below the resonance frequency and a high frequency in the frequency band above the resonance frequency. As a result, the output level decreases. In addition, when the piezoelectric bimorph is lowered in the resonance frequency by increasing the weight fixed to the piezoelectric bimorph, the output level in the frequency band below the resonance frequency increases. Conversely, if the weight fixed to the piezoelectric bimorph is lightened or removed, the resonance frequency moves to a higher frequency, and the output level in the frequency band below the resonance frequency decreases.

  In the conventional throat microphone described at the beginning, it is possible to improve the intelligibility by designing the resonance frequency in a frequency band in which a frictional sound or a plosive sound is generated. Further, in the bone conduction microphone described in Non-Patent Document 1, a plurality of piezoelectric bimorphs having different resonance frequencies are stacked and electrically connected in series to improve clarity. In the invention described in Non-Patent Document 1, if the output level of each piezoelectric bimorph can be mixed by arbitrarily adjusting the output level of each piezoelectric bimorph, the situation of the speaker, for example, whether the speaker is male or not By adjusting finely according to environmental conditions such as being a woman, it is possible to improve clarity. However, as described above, the invention described in Non-Patent Document 1 does not assume that the output level of each piezoelectric bimorph is arbitrarily adjusted.

Denso Technical Review Vol.8 No. 1 2003 "Special feature: Development of bone conduction microphone for speech recognition"

  In the bone conduction microphone described in Non-Patent Document 1, it is difficult to arbitrarily adjust the frequency response characteristics of the stacked individual piezoelectric bimorphs. In the first place, the frequency response of individual piezoelectric bimorphs to the bone conduction microphone described in Non-Patent Document 1 is difficult. There is no idea of arbitrarily adjusting the characteristics.

  The present invention is a further improvement of the conventional technology described above, and in a throat microphone using a piezoelectric bimorph, the frequency response can be adjusted according to the use conditions and environmental conditions, so that sounds including friction sounds and plosive sounds can be clarified. An object of the present invention is to provide a throat microphone capable of collecting sound.

The throat microphone according to the present invention is:
A plurality of piezoelectric bimorphs having different resonance frequencies and being converted into audio signals by receiving vocal cord vibrations,
Each of the piezoelectric bimorphs has an impedance converter that converts its output impedance,
The piezoelectric bimorph is connected to drive another piezoelectric bimorph with the output of the impedance converter of one piezoelectric bimorph, and the output signal of each piezoelectric bimorph is added.
The most important feature is that the input resistance of each impedance converter is variable, and the low-frequency response of each impedance converter output is variable.

  The output signals of each piezoelectric bimorph are added and output. The impedance converter of each piezoelectric bimorph can change the low-frequency response by changing its input resistance. By varying the input resistance in accordance with the use conditions of the throat microphone, for example, the sex of the user, it is possible to adjust the frictional sound and the plosive sound that are difficult to collect to be clearly collected.

It is a circuit diagram which shows the Example of the throat microphone which concerns on this invention. It is a partial cross section side view which shows the example of the piezoelectric bimorph which can be applied to the throat microphone which concerns on this invention. It is a diagram which shows the frequency response characteristic of the output signal of each piezoelectric bimorph in the said Example. It is a diagram which shows the mode of the change of the said frequency response characteristic at the time of varying the input resistance of each impedance converter in the said Example. It is a diagram which shows the frequency response characteristic example of the output signal of the throat microphone obtained by adding the output signal of the several piezoelectric bimorph in the said Example.

  Embodiments of a throat microphone according to the present invention will be described below with reference to the drawings.

  The embodiment shown in FIG. 1 is an example of a throat microphone using a first piezoelectric bimorph 11 and a second piezoelectric bimorph 12. In FIG. 1, one electrode of the first piezoelectric bimorph 11 is connected to the ground, and the other electrode is connected to the gate of a field effect transistor (hereinafter referred to as “FET”). The FET 31 is an active element of a first impedance converter that converts the output impedance of the first piezoelectric bimorph 11 into a low impedance. A DC voltage is supplied from the DC power supply VDD to the drain of the FET 31. The source of the FET 31 is connected to the ground via a resistor 32 and a resistor 33. Between the gate of the FET 31 and the connection point of the resistors 32 and 33, an input resistor 34 of the FET 31 which is an active element of the first impedance converter is connected.

  The input resistor 34 is a variable resistor, and the circuit is configured so that the value of the resistor connected in parallel to the first piezoelectric bimorph 11 can be substantially adjusted by adjusting the value of the input resistor 34. ing. Although the resistor 33 is also a variable resistor, the resistance value between the source of the FET 31 and the ground does not change, and the terminal connected to the slider of the variable resistor 33, that is, the variable terminal is the output terminal of the first piezoelectric bimorph 11. Thus, the output level of the first piezoelectric bimorph 11 is set according to the position of the variable terminal.

  One electrode of the second piezoelectric bimorph 12 is connected to the variable terminal of the variable resistor 33, and the other electrode is connected to the gate of the FET 41. The FET 41 is an active element of a second impedance converter that converts the output impedance of the second piezoelectric bimorph 12 into a low impedance. A DC voltage is supplied from the DC power supply VDD to the drain of the FET 41. The source of the FET 41 is connected to the ground via a resistor 42 and a resistor 43. An input resistor 44 of the FET 41, which is an active element of the second impedance converter, is connected between the gate of the FET 41 and the connection point of the resistors 42 and 43.

  The input resistor 44 is a variable resistor, and the circuit is configured so that the value of the resistor connected in parallel to the second piezoelectric bimorph 12 can be substantially adjusted by adjusting the value of the input resistor 44. ing. Although the resistor 43 is also a variable resistor, the resistance value between the source of the FET 41 and the ground does not change, and the terminal connected to the slider of the variable resistor 43, that is, the variable terminal is the output terminal of the second piezoelectric bimorph 12. Thus, the output level of the second piezoelectric bimorph 12 is set according to the position of the variable terminal. A signal output from the variable terminal of the variable resistor 43 is output from the terminal 52 as an output signal of the throat microphone according to the present embodiment.

  As can be seen from the above description, the first piezoelectric bimorph 11 is connected to drive the second piezoelectric bimorph 12 with the output of the FET 31 as an impedance converter, and the outputs of the first and second piezoelectric bimorphs 11, 12. The signals are added and output.

  The direct-current power supply VDD is external, and is configured such that power is supplied from the external direct-current power supply VDD via the terminal 51 to the throat microphone according to the present embodiment. Reference numeral 53 denotes a ground terminal, which is connected to an external device together with the terminal 52. The input resistors 34 and 44 and the variable resistors 33 and 43 are attached so that the user can operate from the outside of the throat microphone.

  The first and second piezoelectric bimorphs 11 and 12 can be converted into audio signals by receiving vocal fold vibrations, and have different resonance frequencies. The physical configuration of the first and second piezoelectric bimorphs 11 and 12 is not particularly limited, but an example is shown in FIG. In FIG. 2, the piezoelectric bimorphs 11 and 12 are formed in a rectangular plate shape, and have electrodes 16 and 17 and electrodes 18 and 19 on both surfaces at one end in the length direction. First and second piezoelectric bimorphs 11 and 12 are laminated at the electrode forming portion, and a spacer 20 made of an insulating material is interposed between the electrodes 17 and 18 of the adjacent piezoelectric bimorphs 11 and 12.

  A shaft 15 penetrates the electrode forming portion of each piezoelectric bimorph 11, 12 including the spacer 20, and each piezoelectric bimorph is formed by a fastening member 21 such as a nut fixed to the head of the shaft 15 and the tip of the shaft 15. 11 and 12 are integrally fastened at the electrode forming portion. When the head of the shaft 15 is pressed against the throat, the vibration of the vocal cords when sound is generated is transmitted to the shaft 15 through the head, and further transmitted to the first and second piezoelectric bimorphs 11 and 12. It has become.

  The first and second piezoelectric bimorphs 11 and 12 can be converted into audio signals by receiving vocal cord vibration, and the audio signal P1 converted by the first piezoelectric bimorph 11 is transmitted from the electrodes 16 and 17 to the second piezoelectric bimorph. The audio signal P2 converted at 12 is output from the electrodes 17 and 18. The first and second piezoelectric bimorphs 11 and 12 are set to have different resonance frequencies. In the example shown in FIG. 2, the basic specifications of the first and second piezoelectric bimorphs 11 and 12 are the same, and the weights 13 and 14 fixed to the tips of the first and second piezoelectric bimorphs 11 and 12 are made to have different weights. Thus, the resonance frequencies of the first and second piezoelectric bimorphs 11 and 12 are made different. The first and second piezoelectric bimorphs 11 and 12 are electrically connected through the electrodes as shown in FIG.

  In the embodiment shown in FIGS. 1 and 2, the weight of the weight 13 of the first piezoelectric bimorph 11 is heavier than the weight 14 of the second piezoelectric bimorph 12, and the resonance frequency of the first piezoelectric bimorph 11 is the same as that of the second piezoelectric bimorph 12. It is lower than the resonance frequency. A curve P1 shown in FIG. 3 shows the frequency response characteristic of the first piezoelectric bimorph 11, and a curve P2 shows the frequency response characteristic of the second piezoelectric bimorph 12. As is apparent from a comparison between the curve P1 and the curve P2, the weight 13 of the first piezoelectric bimorph 11 is heavy, so that its frequency response characteristic P1 is biased to a lower range than the frequency response characteristic P2 of the second piezoelectric bimorph 12. ing. The output level of the first piezoelectric bimorph 11 is higher than the output level of the second piezoelectric bimorph 12. The peaks of the curves P1 and P2 indicate the output levels at the resonance points of the first and second piezoelectric bimorphs 11 and 12, respectively.

  The frequency response of the first piezoelectric bimorph 11 can be adjusted by adjusting the resistance value of the input resistor 34 shown in FIG. 1, and the frequency response of the second piezoelectric bimorph 12 can be adjusted by adjusting the resistance value of the input resistor 44. Can be adjusted. FIG. 4 shows how the frequency responses of the first and second piezoelectric bimorphs 11 and 12 are changed by varying the input resistors 34 and 44. By changing the input resistances 34 and 44, the values of the input resistances of the FETs 31 and 42 as impedance converters of the first and second piezoelectric bimorphs 11 and 12 are changed. The low cut position in the frequency response of the piezoelectric bimorphs 11 and 12 changes. When the input resistances 34 and 44 of the FETs 31 and 41 are lowered, the frequency response in the low band is lowered and low-cut is performed in a wider range. That is, the low cut position moves to a higher frequency. Therefore, by adjusting the values of the input resistors 34 and 44 in accordance with the characteristics of environmental noise and the like, and adjusting the respective low-cut positions, unnecessary low-frequency noise due to vibration or the like is prevented from being mixed into the audio signal. , Can increase clarity.

  As already described, since the second piezoelectric bimorph 12 is connected to drive the second piezoelectric bimorph 12 with the output of the FET 31 included in the first piezoelectric bimorph 11, the output signals of the piezoelectric bimorphs 11 and 12 are added. An example of the frequency response characteristic of this added signal is shown in FIG. As is clear from FIG. 5, the frequency response characteristic of the added signal is such that the frequency response characteristics of the first and second piezoelectric bimorphs 11 and 12 after impedance conversion are superimposed as shown in FIG. Become. In FIG. 5, two peaks appear at the resonance frequencies of the first and second piezoelectric bimorphs 11 and 12, respectively. In FIG. 5, L1 and L2 indicate output levels at the two peaks. The output level L1 of the resonance frequency of the first piezoelectric bimorph 11 can be changed by adjusting the variable resistor 33 in FIG. Similarly, the output level L2 of the resonance frequency of the second piezoelectric bimorph 12 can be changed by adjusting the variable resistor 43 in FIG.

  As described above, the illustrated embodiment includes the first and second piezoelectric bimorphs 11 and 12, each of the piezoelectric bimorphs 11 and 12 includes the FETs 31 and 41 that convert the output impedance thereof, and the FET 31 included in the preceding piezoelectric bimorph 11. Are connected so as to drive the piezoelectric bimorph 12 at the subsequent stage. The output signals of the piezoelectric bimorphs are added to each other, the FETs 31 and 41 have variable input resistors 34 and 44, and the outputs of the FETs 31 and 41 of the first and second piezoelectric bimorphs 11 and 12 are included. Variable resistors 33 and 43 having variable levels are provided. The low cut positions of the first and second piezoelectric bimorphs 11 and 12 are adjusted by changing the values of the input resistors 34 and 44, and the first and second piezoelectric bimorphs 11 and 12 are adjusted by adjusting the variable resistors 33 and 43. The frequency response characteristic of the throat microphone can be adjusted. In this way, by adjusting the input resistors 34 and 44 or the variable resistors 33 and 43 according to environmental noise and other use conditions, unnecessary low-frequency noise is reduced, and necessary frictional sound and plosive sound are collected. A sound signal with high intelligibility can be obtained.

The throat microphone according to the present invention is not limited to the configuration of the illustrated embodiment, and can be modified as follows.
In order to make the resonance frequencies of the first and second piezoelectric bimorphs 11 and 12 different, basic specifications of the first and second piezoelectric bimorphs 11 and 12, for example, lengths and thicknesses may be made different. Further, the basic specifications of the first and second piezoelectric bimorphs 11 and 12 may be made different, and the weights of the weights 13 and 14 to be fixed may be made different.

  In the example shown in FIGS. 1 and 2, two piezoelectric bimorphs having different resonance frequencies are used, but three or more piezoelectric bimorphs having different resonance frequencies may be used. In that case, each piezoelectric bimorph has an impedance converter that converts its output impedance, and is connected so that the subsequent piezoelectric bimorph is driven by the output of the impedance converter of the preceding piezoelectric bimorph. Thus, the output signals of the piezoelectric bimorphs are added.

  The throat microphone according to the present invention is useful in the case where it is necessary to clearly convey a human voice in an aircraft maintenance shop, a machining site, or other places where the environmental noise level is high. Further, it is useful when it is necessary to clearly transmit a human voice in an environment where voice due to air propagation cannot be communicated, such as underwater work.

11 First Piezoelectric Bimorph 12 Second Piezoelectric Bimorph 13 Weight 14 Weight 31 FET
33 Variable resistance 34 Input resistance 41 FET
43 Variable resistance 44 Input resistance

Claims (5)

A plurality of piezoelectric bimorphs having different resonance frequencies and being converted into audio signals by receiving vocal cord vibrations,
Each of the piezoelectric bimorphs has an impedance converter that converts its output impedance,
The piezoelectric bimorph is connected to drive another piezoelectric bimorph with the output of the impedance converter of one piezoelectric bimorph, and the output signal of each piezoelectric bimorph is added.
A throat microphone in which the input resistance of each impedance converter is variable and the low-frequency response of each impedance converter output is variable.   The throat microphone according to claim 1, further comprising a variable resistor capable of changing an output level of an impedance converter included in each piezoelectric bimorph.   The piezoelectric bimorph has electrodes on both sides at one end in the length direction, a plurality of piezoelectric bimorphs are stacked in the electrode forming portion, a spacer is interposed between the electrodes of adjacent piezoelectric bimorphs, and each piezoelectric bimorph The throat microphone according to claim 1, wherein the throat microphone is integrally fastened at the electrode forming portion.   4. The throat microphone according to claim 1, wherein each piezoelectric bimorph is set to have a different resonance frequency by having weights having different weights. The throat microphone according to any one of claims 1 to 4, wherein each impedance converter includes an FET as an active element.

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