JP4954801B2 - Electroacoustic transducer - Google Patents

Description

  The present invention relates to an electroacoustic transducer such as a condenser type pickup or a stereo microphone.

  As a conventional pickup used for reproducing an analog record board, a speed proportional type such as a moving coil type or a moving magnet type is generally used. Displacement proportional types such as electret capacitor type and RF capacitor type that output signals in proportion to the overlapping area of electrodes facing each other have been manufactured, but are not currently manufactured. Furthermore, an oscillation detection type capacitor type pickup has been put into practical use. Since the present invention relates to an electroacoustic transducer such as an oscillation detection type condenser type pickup or a stereo microphone, the oscillation detection type condenser type electroacoustic transducer will be described below.

The oscillation detection type capacitor type pickup has a problem that the circuit configuration is complicated and adjustment is difficult, but it has a characteristic that the inherent noise is small. In addition, since the output impedance is low, there are advantages such as being less susceptible to noise due to electrostatic coupling and the like, and the adjustment of sound quality is easy because no magnetic material is used.
FIG. 4 shows an example of a conventional phase modulation type oscillation detection type condenser microphone. In FIG. 4, reference numeral 1 is an oscillation circuit, 4 is an oscillation coil, 10 is a ratio detection circuit, and 6 is a resonance coil. The oscillation coil 4 includes three coils L1, L2, and L3 that are magnetically coupled to each other.

  The oscillation circuit 1 includes a transistor 2, a crystal resonator 3, and the coil L1 (tank coil). A capacitor C1 is connected in parallel to the coil L1, a power source PS is connected to one end of the coil L1, and the other end of the coil L1 is connected to the collector of the transistor 2. A resistor R 1 is connected between the collector and base of the transistor 2, a crystal resonator 3 is connected between the base and ground, and a resistor R 2 is connected in parallel with the crystal resonator 3. Capacitors C7 and C8 are also connected in series between the collector and base of the transistor 2, the connection point of the capacitors C7 and C8 is connected to the emitter of the transistor 2, and the emitter is connected to the ground via the resistor R3. ing. The coils L2 and L3 are connected in series, and this connection point is connected to the ground. The oscillation circuit 1 stabilizes the oscillation frequency by configuring an oscillation circuit including the crystal resonator 3.

  The resonance coil 6 includes three coils L4, L5, and L6 that are magnetically coupled to each other. The ratio detection circuit 10 is one of demodulation methods for phase-modulated signals, and is a circuit method for generating a phase difference by coupling coils L5 and L6 and a capacitor and demodulating in a vector manner. The condenser is formed between a condenser microphone unit 5, more specifically, a diaphragm constituting the condenser microphone unit and a fixed electrode facing the diaphragm with a gap. It is a condenser. The coils L5 and L6 are connected in series. The other end of the coil L5 is connected to the microphone output terminal OUT via the diode 7, and the other end of the coil L6 is connected to the microphone output terminal OUT via the diode 8. The diodes 7 and 8 are opposite to each other.

  The oscillation circuit 1 oscillates a high frequency of about 8 MHz to 12 MHz, for example, and in order to supply the oscillated high frequency from the oscillation coil 4 to the resonance coil 6, one end of the coil L2 and one end of the coil L4 are connected, and one end of the coil L3 is connected. Is connected to the connection point of the coils L5 and L6. The high frequency signal oscillated by the oscillation circuit 1 is supplied from the coils L2 and L3 to the resonance coil 6. The capacitance of the microphone unit 5 is connected in series to the coil L4 constituting the resonance coil 6. The condenser microphone unit 5 vibrates in accordance with the sound wave received by the diaphragm, so that the capacitance changes. A resonance circuit is constituted by the capacitance of the microphone unit 5 and the inductance of the resonance coil 6, and a high frequency signal generated by the oscillation circuit 1 is added to the resonance circuit as a bias. The high-frequency signal is phase-modulated with an audio signal that has been electroacoustic converted by the microphone unit 5. This modulation signal is demodulated by the ratio detection circuit 10 and output from the microphone output terminal OUT. Since the coil L4 constituting the resonance coil 6 resonates in series with the capacitance of the microphone unit 5, the impedance at the resonance frequency becomes extremely low. Thus, unless the impedance at the resonance frequency is lowered, the sensitivity is lowered.

The analog record board playback pickup is configured to play back the left and right channel audio signals carved in the groove of the record board and output the left and right signals. The oscillation detection type pickups that have been commercialized so far require two oscillators having separate oscillation frequencies for the left and right channels, and two detectors corresponding to each oscillator.
However, if two oscillators that transmit two different frequency signals are built in, interference between the two frequency signals is likely to occur, so that the oscillation frequency does not interfere even after the two oscillators are built in the pickup body. It was necessary to adjust the oscillator or adjust the inductance of the detection coil. In addition, since the oscillation frequency adjustment method is based on, for example, VFO, frequency drift occurs, and it is necessary to frequently adjust the oscillation frequency. However, this type of adjustment requires a high level of technology, and it is difficult for a general user to make adjustments.

Even when the oscillation detection type condenser microphone is a stereo microphone, the conventional idea requires two oscillators having different oscillation frequencies corresponding to the left and right microphone units and two detection circuits corresponding to the respective oscillators. However, when a plurality of oscillators are used, the oscillation signals interfere with each other unless the microphone cases are separated, so that the outer shape becomes large and the usability as a stereo microphone becomes worse.
Oscillation detection type microphones are used in studios and the like because of their low noise. In the case of a studio, it is necessary to have a balanced output, and it is necessary to devise a circuit configuration to enable balanced output.

As a capacitor type electroacoustic transducer, a capacitor type transducer described in Patent Document 1, a capacitance-voltage conversion device described in Patent Document 2, and a pickup device described in Patent Document 3 are known. ing.
All of the inventions described in these patent documents belong to the oscillation detection system. However, in any of the inventions described in the patent documents, there is no description regarding the recognition of the above-mentioned technical problems occurring in an electroacoustic transducer having a plurality of oscillators and corresponding detection circuits, and means for solving the problems. There is no.

Japanese Utility Model Publication No. 49-38643 Japanese Utility Model Publication No. 49-30122 Japanese Patent Publication No.49-33641

The present invention relates to an oscillation detection type electroacoustic transducer capable of electroacoustic conversion output of two systems, such as a pickup for reproducing a record board or a stereo microphone, and includes two resonance circuits and two demodulations with a single oscillator. An object of the present invention is to provide an electroacoustic transducer in which the circuit configuration is devised so that the circuit can be operated, and thus the adjustment of the oscillation frequency is simplified or unnecessary.
Another object of the present invention is to enable balanced output when the electroacoustic transducer is a stereo microphone.

  An electroacoustic transducer according to the present invention includes an oscillation circuit including an oscillation coil and a crystal resonator, and is biased by a high-frequency signal that is coupled to the oscillation circuit via a coupling unit and is generated by the oscillation circuit, and is also a capacitor-type electroacoustic An electric circuit comprising: a resonance circuit constituted by the capacitance of the conversion means and the resonance coil; and a demodulation circuit that demodulates the output signal of the resonance circuit into a signal corresponding to the capacitance change of the capacitor-type electroacoustic conversion unit. An acoustic transducer, wherein the oscillation circuit includes a transistor and an oscillation coil that are symmetrically connected to both ends of a crystal resonator, and the resonance circuit is connected to both ends of an oscillation coupling coil that is magnetically coupled to the oscillation coil. Two resonance coils connected to each other and capacitor type electroacoustic conversion means of different systems connected to each resonance coil. The most important feature in that it consists of two demodulation circuits for demodulating the signal corresponding to the capacitance change of each capacitor electroacoustic transducing means from the output signal of the resonant circuit.

The oscillation circuit is one oscillation circuit including one crystal resonator, and signals having the same frequency are output by the transistors and the oscillation coils that are symmetrically connected to both ends of the crystal resonator. This signal is input to each resonance coil of the two resonance circuits, and biases the two resonance circuits. Each resonance coil is connected to the electrostatic capacity of the condenser type electroacoustic conversion means of a different system from each other, and a signal corresponding to the capacitance change of each capacitor type electroacoustic conversion means is output from each demodulation circuit.
Although there is only one oscillation circuit, signals from different systems can be output from the two demodulation circuits. Therefore, it is not necessary to provide two resonance circuits corresponding to the two demodulation circuits as in conventional oscillation detection pickups and the like, and a single oscillation frequency is sufficient, so there is no problem of interference between oscillation signals. The oscillation frequency is also stabilized, and the adjustment of the oscillation frequency can be simplified or made unnecessary.

  Embodiments of an electroacoustic transducer according to the present invention will be described below with reference to the drawings.

  In FIG. 1, reference numeral 11 is an oscillation circuit, 14 is an oscillation coil, 70 and 80 are ratio detection circuits, and 61 and 62 are resonance coils. The oscillation coil 14 includes four coils L11, L12, L13, and L14 that are magnetically coupled to each other.

  The oscillation circuit 11 includes two transistors 21 and 22, one crystal resonator 3, and the coils L11 and L12 (tank coils). A power source PS is connected to the connection point of the coils L11 and L12, the other end of the coil L11 is connected to the source of a field effect transistor (hereinafter referred to as “FET”) 21, and the other end of the coil L12 is connected to the source of the FET 22. Yes. A resistor R21 is connected between the drain of the FET 21 and the ground G, a resistor R22 is connected between the base and the ground G, and one end of the crystal unit 3 is connected to the base. A resistor R24 is connected between the drain of the FET 22 and the ground G, a resistor R23 is connected between the base and the ground G, and the other end of the crystal unit 3 is connected to the base. As described above, the oscillation circuit includes the FETs 21 and 22 and the oscillation coil 14 that are symmetrically connected to both ends of the crystal resonator 3. The oscillation circuit 11 configured as described above oscillates with a specific frequency signal determined by the natural frequency of the crystal resonator 3, and this signal is output from the oscillation coils L11 and L12. The oscillation circuit 11 stabilizes the oscillation frequency by configuring an oscillation circuit including the crystal resonator 3.

  The resonance coil 61 has two coils L41 and L51 magnetically coupled to each other, and the resonance coil 62 also has two coils L42 and L52 magnetically coupled to each other. The coils L41 and L42 are original resonance coils, and the coils L51 and L52 are herein referred to as “resonance coupling coils”. The ratio detection circuits 70 and 80 are one of the demodulation methods of the phase-modulated signal. The ratio detection circuit 70 creates a phase difference by coupling the coil L41 and the capacitor, and the ratio detection circuit 80 couples the coil L42 and the capacitor. This is a circuit system in which a phase difference is generated by the above and demodulated in a vector manner. The condenser is a condenser provided in a condenser type pickup unit. More specifically, as shown in FIG. 2, the movable electrode formed on the outer peripheral surface of the cantilever 50 constituting the condenser type pickup unit and the fixed electrode facing the movable electrode with a gap therebetween. Two capacitors are formed between the electrodes 51 and 52, respectively. A needle that traces the sound groove of the record is attached to the tip of the cantilever 50, and the cantilever 50 moves when the needle vibrates according to the unevenness of the sound groove. The gap changes. The fixed electrodes 51 and 52 face the movable electrode formed on the cantilever 50 with a central angle of 90 degrees. By moving the cantilever 50 as described above, the gap between the movable electrode and the fixed electrodes 51 and 52 changes, and the capacitance of each capacitor changes. The fixed electrode 51 is an output terminal of the left (L) channel and is connected to the coil L41, and the fixed electrode 52 is an output terminal of the right (R) channel and is connected to the coil L42.

  The other ends of the coils L41 and L42 are connected to respective ends of a coil L14 (hereinafter referred to as “oscillation coupling coil”) magnetically coupled to the oscillation coils L11 and L12. The oscillation coupling coil L14 has a center tap, and the center tap is grounded. One end of the resonance coupling coil L51 magnetically coupled to the coil L41 constituting the coupling coil 61 is connected to the L channel output terminal LOUT via the diode 71, and the other end of the coil L51 is connected to the L channel output terminal LOUT via the diode 72. It is connected to the. The diodes 71 and 72 are opposite to each other. One end of the resonance coupling coil L52 magnetically coupled to the coil L42 constituting the coupling coil 62 is connected to the R channel output terminal ROUT via the diode 81, and the other end of the coil L52 is connected to the R channel output terminal ROUT via the diode 82. It is connected to the. The diodes 81 and 82 are opposite to each other. The resonance coupling coils L51 and L52 have center taps, and these center taps are connected to respective ends of a reference frequency generation coil L13 that is magnetically coupled to the oscillation coils L11 and L12. The reference frequency generating coil L13 has a center tap, and this center tap is grounded. A capacitor C91 is connected between the L channel output terminal LOUT and the ground, and a capacitor C92 is connected between the R channel output terminal ROUT and the ground.

The oscillation circuit 11 oscillates a high frequency of, for example, about 8 MHz to 12 MHz, and supplies the oscillated high frequency signal from the oscillation coil 14 to the resonance coils 61 and 62, so that each end of the coupling coil L14 constitutes the resonance coils 61 and 62. Connected to one end of the coils L41 and L42. The movable electrodes formed on the cantilever 50 of the pickup unit, which is one of the electroacoustic transducers, are connected to the ground G at the other ends of the coils L41 and L42.
The high frequency signal oscillated by the oscillation circuit 11 is supplied from the coupling coil L14 to the resonance coils 61 and 62. Capacitances of the left and right channels of the capacitor type pickup unit are connected in series to the coils L41 and L42 constituting the resonance coils 61 and 62, respectively. In the pickup unit, the capacitance of the left and right channels changes according to the vibration of the cantilever 50. A resonance circuit is constituted by the capacitance of the left channel and the inductance of the resonance coil L41. Similarly, a resonance circuit is constituted by the capacitance of the right channel and the inductance of the resonance coil L42. Apply the signal as a bias. The high-frequency signal is phase-modulated with a signal that has been electroacoustic converted by the pickup unit. This modulation signal is demodulated by the ratio detection circuits 70 and 80 and output from the left channel output terminal LOUT and the right channel output terminal ROUT. Since the coils L41 and L42 constituting the resonance coils 61 and 62 resonate in series with the capacitance of the pickup unit, the impedance at the resonance frequency becomes low.

  In the first embodiment described above, the oscillation circuit 11 includes the FETs 21 and 22 and the oscillation coil 14 that are symmetrically connected to both ends of the crystal resonator 3, and the resonance circuit is magnetically coupled to the oscillation coil 14. And two resonance coils L41 and L42 connected to both ends of the oscillation coupling coil L14, and an electroacoustic conversion unit of a pickup which is a capacitor type electroacoustic conversion unit of a separate system connected to each resonance coil. Two demodulation circuits 70 and 80 are provided for demodulating the output signals of the respective resonance circuits into signals corresponding to the capacitance changes of the respective capacitor-type electroacoustic conversion means. Therefore, one oscillation circuit 11 is sufficient to output two systems of signals, and it is not necessary to provide two oscillation circuits. Therefore, the circuit configuration can be simplified and interference between oscillation signals can be reduced. The problem disappears. Since fine adjustment of the oscillation frequency is also unnecessary, it can be used without special technical ability, and the problem of frequency drift is eliminated.

  FIG. 3 shows a second embodiment of the electroacoustic transducer according to the present invention. This embodiment is an example of an oscillation detection system condenser type stereo microphone. This embodiment is different from the first embodiment shown in FIG. 1 in that the electroacoustic conversion unit is a condenser microphone unit, and a configuration is added to the demodulation circuit in order to make the left and right channel outputs balanced. Is different. Therefore, different reference numerals are given to different constituent parts, the same constituent parts are assigned the same reference numerals as those of the first embodiment, and the description overlapping with the description of the first embodiment will be simplified.

  In FIG. 3, reference numerals 53 and 54 denote left and right channel condenser microphone units, respectively. The condenser microphone unit 53 includes a vibration plate 55 that vibrates in response to sound waves, and a fixed electrode 56 that faces the vibration plate 55 with a predetermined gap therebetween. A condenser is interposed between the vibration plate 55 and the fixed electrode 56. It is composed. Similarly, the condenser microphone unit 54 also includes a diaphragm 57 and a fixed electrode 58, and a capacitor is configured between the diaphragm 57 and the fixed electrode 58. The diaphragms 55 and 57 are both grounded, the fixed electrode 56 is connected to one end of the resonance coil L41, and the fixed electrode 58 is connected to one end of the resonance coil L42. The resonant coils 61 and 62 have two coils L51 and L61, and L52 and L62, respectively, which are magnetically coupled to the coils L41 and L42.

  The left channel coils L51 and L61 are provided with center taps. These center taps are connected to one end of a reference frequency generating coil L13 magnetically coupled to the oscillation coils L11 and L12, and are generated by the coil L13. A reference frequency signal is input. Similarly, the right-channel coils L52 and L62 also have center taps, and the other end of the reference frequency generating coil L13 is connected to these center taps, and a reference frequency signal generated by the coil L13 is input thereto. It is like that. Diodes 73 and 74 are connected in opposite directions to both ends of the coil L51 to form a ratio detection circuit 101 as a demodulation circuit. The output of the ratio detection circuit 101 is connected to one output line of the left channel output LOUT. linked. Diodes 75 and 76 are connected in opposite directions to both ends of the coil L61 to form another ratio detection circuit 102. The output of the ratio detection circuit 102 is connected to the other output line of the left channel output LOUT. Yes. The outputs of the two ratio detection circuits 101 and 102 are balanced and output as the left channel output LOUT.

The right channel resonance circuit and the ratio detection circuit as a demodulation circuit are configured in the same manner. That is, diodes 83 and 84 are connected in opposite directions to both ends of the coil L52 to constitute a ratio detection circuit 103, and the output of the ratio detection circuit 103 is connected to one output line of the right channel output ROUT. . Diodes 85 and 86 are connected in opposite directions to both ends of the coil L62 to form another ratio detection circuit 104. The output of the ratio detection circuit 103 is connected to the other output line of the right channel output ROUT. Yes. The outputs of the two ratio detection circuits 103 and 104 are balanced and output as the right channel output ROUT.
Since other configurations are the same as those of the first embodiment, description thereof will be omitted.

  In the second embodiment described above, the capacitances of the left and right channel condenser microphone units 53 and 54 are connected in series to the coils L41 and L42 constituting the resonance coils 61 and 62, respectively. In each of the microphone units 53 and 54, the capacitance between the fixed electrodes 56 and 58 changes when the diaphragms 55 and 57 are vibrated by receiving sound waves. A resonance circuit is constituted by the capacitance of the left channel and the inductance of the resonance coil L41. Similarly, a resonance circuit is constituted by the capacitance of the right channel and the inductance of the resonance coil L42. Apply the signal as a bias. The high-frequency signal is phase-modulated by a signal that has been electroacoustic converted by a condenser microphone unit. The modulation signal from the left channel microphone unit 53 is demodulated by the ratio detection circuits 101 and 102 of the left channel. The two ratio detection circuits 101 and 102 output signals having opposite phases to each other, and are balanced and output from these signal lines as the left channel output terminal LOUT. The same applies to the right channel. The modulation signal from the right channel microphone unit 54 is demodulated by the ratio detection circuits 103 and 104 of the right channel. The two ratio detection circuits 103 and 104 output signals having opposite phases to each other, and are balanced and output from these signal lines as the right channel output terminal ROUT.

  In the second embodiment described above, the same effects as in the first embodiment can be obtained, and two demodulation circuits having different output signal polarities are connected to the left and right channels, respectively. Since the balanced output is made by the output of the circuit, for example, an oscillation detection type stereo condenser microphone that can be used in a studio can be obtained.

1 is a circuit diagram showing a first embodiment of an electroacoustic transducer according to the present invention. FIG. It is a side view which shows the principal part of the electroacoustic conversion part used for the said 1st Example. It is a circuit diagram which shows the 2nd Example of the electroacoustic transducer which concerns on this invention. It is a circuit diagram which shows the example of the conventional electroacoustic transducer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Crystal oscillator 11 Oscillation circuit 14 Oscillation coil 51 Fixed electrode 52 Fixed electrode 55 Diaphragm 56 Fixed electrode 57 Diaphragm 58 Fixed electrode 53 Condenser microphone unit 54 Condenser microphone unit 61 Resonance coil 62 Resonance coil 70 Ratio detection circuit 80 Ratio detection circuit DESCRIPTION OF SYMBOLS 101 Ratio detection circuit 102 Ratio detection circuit 103 Ratio detection circuit 104 Ratio detection circuit L11 Oscillation coupling coil L12 Oscillation coupling coil L13 Reference frequency generation coil

Claims (6)

An oscillation circuit including an oscillation coil and a crystal unit;
A resonance circuit coupled to the oscillation circuit via a coupling means and biased by a high-frequency signal generated by the oscillation circuit and configured by a capacitance of a capacitor-type electroacoustic conversion means and a resonance coil;
A demodulating circuit that demodulates the output signal of the resonance circuit into a signal corresponding to the capacitance change of the capacitor-type electroacoustic conversion unit, and an electroacoustic transducer comprising:
The oscillation circuit includes a transistor and an oscillation coil that are symmetrically connected to both ends of the crystal resonator,
The resonance circuit includes two resonance coils connected to both ends of an oscillation coupling coil magnetically coupled to the oscillation coil, and capacitor-type electroacoustic conversion means of different systems connected to each resonance coil,
The demodulator circuit is an electroacoustic transducer comprising two demodulator circuits that demodulate the output signal of each resonance circuit into a signal corresponding to the capacitance change of each capacitor type electroacoustic transducer.   The condenser-type electroacoustic conversion means is a condenser-type pickup for reproducing a record board, and includes a movable electrode integral with the cantilever and a movable electrode that is opposed to the movable electrode with a central angle of 90 degrees to form a condenser. The electroacoustic transducer according to claim 1, further comprising a fixed electrode.   Each of the two resonance coils includes a resonance coupling coil magnetically coupled thereto, and diodes constituting a ratio detection circuit as a demodulation circuit are respectively connected to both ends of each resonance coupling coil. 2. The electroacoustic transducer according to claim 1, wherein a reference frequency signal generated by a reference frequency generating coil magnetically coupled to the oscillation coil is input.   The electroacoustic transducer according to claim 1, wherein the condenser-type electroacoustic conversion means is a denser microphone unit, and a stereo microphone is configured by providing two of the microphone units.   5. The electroacoustic transducer according to claim 4, wherein the two demodulation circuits each include two ratio detection circuits that output signals of opposite polarities, and the outputs of the two ratio detection circuits of each demodulation circuit are balanced outputs.   Each of the two resonance coils is provided with two resonance coupling coils magnetically coupled to each of them, and a ratio detection circuit as a demodulation circuit is formed at each end of each of the two resonance coupling coils magnetically coupled to each resonance coil. 6. The electroacoustic transducer according to claim 5, wherein a reference frequency signal generated by a reference frequency generating coil magnetically coupled to the oscillation coil is input to each of the coupling coils.

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