JP4947708B2 - Condenser microphone unit and condenser microphone - Google Patents

Description

  The present invention relates to a condenser microphone unit and a condenser microphone using the same. It is possible to prevent an excessive signal from being input to an impedance converter by automatically adjusting sensitivity.

  An electret condenser microphone, which is a kind of electrostatic microphone, includes a condenser microphone unit that is an electroacoustic transducer in which a diaphragm and a fixed pole are opposed to each other with a predetermined gap. Since the condenser microphone unit has a very high impedance, the output impedance is reduced to several hundred to several thousand ohms by, for example, incorporating an impedance converter mainly composed of a field effect transistor (hereinafter referred to as “FET”).

Further, when an excessive sound pressure is applied to the condenser microphone, distortion occurs in the output of the impedance converter mainly composed of the FET. Therefore, when an excessive input is predicted in advance, there is one in which the sensitivity is lowered by attenuating an electric signal input to the impedance converter using an input attenuator (hereinafter referred to as “PAD”). Since the PAD is usually configured by connecting an attenuating capacitor in parallel with the effective capacity of the condenser microphone unit, the sound quality may be deteriorated depending on the quality of the capacitor.
Therefore, in a high-quality condenser microphone used for studio recording or the like, it is necessary to select and use a high-quality condenser that does not deteriorate sound quality as an attenuating condenser. In addition, according to the condenser microphone using PAD, the attenuation amount is set by selecting the capacitance of the attenuation condenser by operating the switch, so that when an unpredictable excessive sound pressure occurs, the output signal of the impedance converter Distortion cannot be prevented.

The present applicant has previously filed a patent application regarding a condenser microphone unit in which an attenuator condenser unit connected to the condenser microphone unit is a variable capacitance unit using, for example, a piezoelectric element. Japanese Patent Application No. 2006-304051 has not yet been published. In the above patent application, as an example, a voltage obtained by converting the output signal of the microphone unit into a direct current is used as the driving voltage for the piezoelectric element of the variable capacitance unit.
However, even in the invention according to the above application, the sound quality deteriorates due to the capacitor or the sound quality changes due to the capacitance switching.

The applicant has also filed a patent application for an electret condenser microphone that allows the sensitivity to be adjusted without the use of an attenuating condenser or amplifier. A microphone unit having an electret dielectric film on either one of a diaphragm and a fixed pole arranged opposite to each other, and an impedance converter composed of a FET connected to the fixed pole and operated by a source follower, and the gate of the FET, In addition to being connected to a fixed pole through a capacitor, sensitivity is adjusted by applying a predetermined voltage supplied from a phantom power source to the fixed pole or diaphragm (see Patent Document 1).
JP 2006-295357 A

  According to the invention described in Patent Document 1, since the sensitivity is adjusted by automatically changing the capacitance of the condenser composed of the diaphragm and the fixed pole, a condenser as an individual part is unnecessary, and the sound quality is deteriorated by the condenser. , Can avoid the change of sound quality. However, when used in an environment where loud sound is generated, there is a delay in operating time from the generation of loud sound until the sensitivity is attenuated, and due to this delay in operating time, the loud sound is instantaneously input to the impedance converter and its output Signal distortion cannot be completely avoided.

  The present invention solves the problems of the conventional condenser microphone described above, that is, it is unavoidable that a delay in operation time occurs from the generation of a large sound until the sensitivity is attenuated. The purpose of the present invention is to provide a condenser microphone unit and a condenser microphone that can reliably reduce the signal level input to the impedance conversion circuit without timing delay and prevent distortion of the output signal of the impedance conversion circuit. To do.

The present invention provides a main microphone mainly composed of an electret condenser microphone unit, a sub-microphone disposed at a predetermined distance in front of the main microphone, and an output signal level of the sub-microphone when the level is equal to or higher than a predetermined level. a signal level detecting circuit for reducing the polarization voltage by applying a voltage to the electret condenser microphone unit, a condenser microphone unit comprising comprising an impedance converting circuit to which an output signal of the electret condenser microphone unit is input, the main The distance between the microphone and the sub microphone is the time from when the loud sound enters the sub microphone until the signal level detection circuit applies a voltage to the electret condenser microphone unit to lower the polarization voltage. The most important being a distance commensurate with the delay.

  The sound enters the main microphone with a delay after entering the secondary microphone. When the large sound enters the sub microphone, the signal level detection circuit detects this, and the voltage is applied to the electret condenser microphone unit of the main microphone mainly composed of the electret condenser microphone unit to lower the polarization voltage. As a result, the sensitivity of the electret condenser microphone unit is lowered, and the level of the signal input to the impedance conversion circuit is lowered. Until the large sound enters the main microphone, the sensitivity adjustment operation of the electret condenser microphone unit as described above is performed, and the distortion of the output signal of the impedance conversion circuit caused by the large sound input is prevented.

Hereinafter, embodiments of a condenser microphone unit and a condenser microphone according to the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a main microphone, and 2 denotes a sub microphone. The main microphone 1 is mainly composed of an electret condenser microphone unit, and includes a diaphragm 11 and a fixed pole 13 made of a conductor disposed opposite to the diaphragm 11, and the fixed pole 13 is electret on the surface facing the diaphragm 11. An electret layer 14 made of a dielectric film is provided. The outer peripheral edge of the diaphragm 11 is fixed to one surface side of the ring-shaped diaphragm holder 12 with an appropriate tension. An appropriate gap is formed between the diaphragm 11 and the fixed pole 13 by means such as interposing a spacer, and the diaphragm 11 and the electret layer 14 of the fixed pole 13 constitute a capacitor. A condenser microphone unit component including a diaphragm holder 12 to which the diaphragm 11 is fixed and a fixed pole 13 having an electret layer 14 is incorporated in a unit case (not shown). The unit case also serves as a ground and is electrically connected to the diaphragm 11. The fixed pole 13 serves as an output terminal of the microphone unit and is connected to an impedance conversion circuit described below.

  The impedance conversion circuit is mainly composed of the FET 6. The positive electrode of the power source 7 is connected to the source of the FET 6, and the negative electrode of the power source 7 is grounded. The fixed pole 13 of the main microphone 1 is connected to the base of the FET 6 via a capacitor 17 so that the output signal of the main microphone 1 is input. Two load resistors 19 and 20 are connected in series to the drain of the FET 6, and the drain is connected to the output terminal 8. A bias resistor 18 is connected between the connection point of the load resistors 19 and 20 and the base.

  The electroacoustic conversion method of the sub microphone 2 is arbitrary, and is not limited to the condenser type microphone. The sub microphone 2 is disposed in front of the main microphone 1, and a predetermined distance D is placed between the diaphragm of the sub microphone 2 and the diaphragm 12 of the main microphone 1.

  The output signal of the sub microphone 2 is configured to be input to the signal level detection circuit 10. The signal level detection circuit 10 detects the output signal level of the sub-microphone 2 and applies a voltage to the electret condenser microphone unit constituting the main microphone 1 when the level is equal to or higher than a predetermined level to lower the polarization voltage. The circuit configuration is as follows. The signal level detection circuit 10 determines whether the output signal level of the sub microphone 2 is equal to or higher than a predetermined level, and applies a voltage to the electret condenser microphone unit to reduce the polarization voltage when the level is higher than the predetermined level. 4 is provided. More specifically, the signal level detection circuit 10 includes an amplifier 3 in front of the comparison circuit 4. The comparison circuit 4 determines whether the output level of the amplifier 3 is equal to or higher than a predetermined level. Is determined to be equal to or higher than a predetermined level, the output signal of the amplifier 3 is rectified to generate a voltage to be applied to the electret condenser microphone unit.

  The signal rectified by the rectifier 5 is smoothed by the capacitor 16 and is applied to the fixed pole 13 of the electret condenser microphone unit via the resistor 15. Accordingly, when a large sound having a predetermined sound pressure or higher enters the sub microphone 2, the signal level detection circuit 10 including the comparison circuit 4 detects the sound pressure of the large sound amplified by the amplifier 3 and rectified by the rectifier 5. Is applied to the fixed electrode 13 through the resistor 15.

  The electret layer 14 formed on the fixed pole 13 of the electret condenser microphone unit originally has a predetermined polarization voltage, and when the voltage is applied from the signal level detection circuit 10, the polarization voltage is equivalent. The sensitivity of the main microphone 1 decreases. Therefore, if the sensitivity of the main microphone 1 is reduced as described above prior to the large sound entering the main microphone 1, the sensitivity decreases when the large sound enters the main microphone 1. Therefore, it is possible to avoid an excessive signal being input to the impedance conversion circuit mainly composed of the FET 6, and to prevent the output signal of the impedance conversion circuit from being distorted.

  As described above, in order to reduce the sensitivity of the main microphone 1 before the large sound enters the main microphone 1, the distance D between the main microphone 1 and the sub microphone 2 is set to a predetermined value necessary for achieving the purpose. Must be set to a distance or more. The propagation speed of sound waves in the air is 340 m / sec on average, and the distance D calculated from the propagation speed of the sound waves and the signal processing speed of the signal level detection circuit 10 is the distance D.

  Also, the time required from when the large sound is input to the sub microphone 2 until the signal level detection circuit 10 detects that there is an excessive input due to the large sound and applies a voltage to the fixed electrode 13 of the electret condenser microphone unit. (Operation delay time) is determined by the time constant determined by the capacitance of the capacitor 16 constituting the smoothing circuit and the value of the resistor 15. Therefore, it is necessary to design the capacitance of the capacitor 16 and the value of the resistor 15 based on the operation time (operation delay time) required for the signal level detection circuit 10.

  Among the components shown in FIG. 1, at least the main microphone 1 and the sub microphone 2 can be combined into a single microphone case to form a condenser microphone. All the components including the impedance conversion circuit and the signal level detection circuit 10 as shown in FIG. 1 may be incorporated in the microphone case.

It is a circuit diagram which shows the Example of the condenser microphone unit and condenser microphone concerning this invention.

Explanation of symbols

1 Main microphone 2 Sub microphone 3 Amplifier 4 Comparator 5 Rectifier 6 FET
11 Diaphragm 13 Fixed pole 14 Electret layer

Claims (6)

A main microphone mainly composed of an electret condenser microphone unit;
A secondary microphone are arranged at a predetermined distance in front of the main microphones,
A signal level detecting circuit for reducing the polarization voltage by applying a voltage to said electret condenser microphone unit detects the output signal level of the sub microphones in the case of more than a predetermined level,
An impedance conversion circuit to which an output signal of the electret condenser microphone unit is input,
A condenser microphone unit comprising :
The distance between the main microphone and the sub-microphone is the operation from when the loud sound enters the sub-microphone until the signal level detection circuit applies a voltage to the electret condenser microphone unit to reduce the polarization voltage. Condenser microphone unit that is a distance commensurate with the time delay. The electret condenser microphone unit, the vibrating plate and includes a fixed electrode disposed opposite to said diaphragm, said fixed electrode includes an electret layer on the opposite surface of said diaphragm, said signal level detecting circuit is the electret layer 2. The condenser microphone unit according to claim 1, wherein a voltage is applied to the capacitor microphone unit. The signal level detection circuit includes a comparator circuit for the output signal level to determine whether more than a predetermined level, reducing the polarization voltage by applying a voltage to said electret condenser microphone unit in the case of more than a predetermined level The condenser microphone unit according to claim 1 or 2 . 4. The condenser microphone unit according to claim 3, wherein the signal level detection circuit includes an amplifier before the comparison circuit. The signal level detection circuit includes an amplifier, a comparator circuit output level of the amplifier to determine if more than a predetermined level, the output signal of the amplifier when the comparator circuit is equal to or greater than a predetermined level condenser microphone unit according to claim 1 or 2 and a rectifier for generating a voltage to be applied to the electret condenser microphone unit to rectify. A condenser microphone in which the microphone unit is incorporated in a microphone case, wherein the condenser microphone unit according to any one of claims 1 to 5 is incorporated in one microphone case.

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