JP4977379B2 - Diaphragm tension measuring device - Google Patents

Description

  The present invention relates to a diaphragm tension measuring device for measuring the tension of a diaphragm used in a condenser microphone, and more particularly, to a technique for measuring the tension of a diaphragm in a continuously oscillating state. .

  Condenser microphones have an acoustic-electric converter with a diaphragm and a fixed pole that are vibrated by sound waves facing each other, but the low-frequency limit of primary sound pressure gradient type (unidirectional) condenser microphones. And the adsorption stability for the fixed pole depends on the tension of the diaphragm. For this reason, it is necessary to reduce variations in the tension of the diaphragm in order to make the quality of the low frequency limit and the adsorption stability uniform in each condenser microphone.

  Usually, the diaphragm is applied to a large-sized mother film with a predetermined tension, and a plurality of support rings are placed on it via adhesives. The adhesive is cured and each support with diaphragms is supported from the mother film. It is made by cutting out a ring. In the present specification, a structure in which a diaphragm is stretched on a support ring may be referred to as a diaphragm unit.

  For diaphragm units for general-purpose condenser microphones, individual tension measurements are generally not performed in the state of the diaphragm unit. However, high performance is especially required in the case of condenser microphones for studios where sound quality is particularly important. It is required that the difference in sound quality is small (the allowable range of individual differences is generally specified within 10%).

  Conventionally, diaphragm tension measurement methods can be broadly divided into a method of vibrating the diaphragm with sound waves and measuring its amplitude, and a vibration plate vibrating with an alternating magnetic field to detect the level of sound waves emitted at that time. In any of these methods, basically, the frequency for driving the diaphragm is adjusted, and the resonance frequency is measured with the maximum amplitude and sound volume.

  When measuring this resonance frequency, a sweep oscillator is usually used to adjust the drive frequency. While operating the sweep oscillator, check the level with an oscilloscope, etc., and read the frequency when the level shows maximum. Yes.

  However, when operating the sweep oscillator, if the frequency is swept from lower to higher, the reading will be higher than the true value, and conversely if the frequency is swept from higher to lower, the reading will be higher than the true value. May be lower. Further, since the error due to this operation depends on the sweep speed, there is a problem that the measurement reliability is generally low.

  Therefore, in order to solve this problem, the applicant of the present invention radiates from the driving electrode disposed with a predetermined gap with respect to the diaphragm (object to be measured) stretched on the support ring, and the diaphragm. A measurement microphone for picking up sound waves, a voltage amplifier for amplifying a microphone output signal output from the measurement microphone and applying the amplified output signal to the drive electrode to electrostatically drive the diaphragm, and the microphone output signal Patent application No. 2004-286152 has been filed for a diaphragm tension measuring device provided with a frequency counter for measuring the frequency.

  According to the prior invention of Japanese Patent Application No. 2004-286152, a loop is formed in which the microphone output signal of the measurement microphone by the sound wave radiated from the diaphragm is applied to the drive electrode via the voltage amplifier, thereby forming the microphone and the speaker. The diaphragm oscillates in a manner similar to the state in which it causes howling.

  At this time, when the diaphragm tension is high, it oscillates at a high frequency, and when the diaphragm tension is low, it oscillates at a low frequency. Therefore, the diaphragm tension is measured by reading the oscillation frequency with a frequency counter. can do. Therefore, since it is not necessary to manually operate the sweep oscillator as in the conventional example, there is almost no room for the individual difference of the measurer to intervene in the measurement value, and highly reliable measurement can be performed.

  In the prior invention, since the sound waves emitted from the diaphragm are collected by the microphone, there is no particular problem if the surroundings are extremely quiet. However, when measurement is performed in a noisy environment, the sound wave emitted from the diaphragm may be erased by the noise, which makes measurement difficult.

  If the sound wave radiated from the diaphragm is increased, the tension of the diaphragm can be measured even in a noisy environment. However, in this case, since it is necessary to apply a large alternating magnetic field from the driving electrode to the diaphragm, a spark discharge occurs between the driving electrode and the diaphragm depending on the magnitude of the alternating magnetic field, and the diaphragm is burned out. This is not a preferable solution.

  Therefore, an object of the present invention is to make it possible to measure the tension of the diaphragm with high reliability even in an environment where noise exists in the environment where there is almost no room for the individual difference of the measurer to intervene.

In order to solve the above-mentioned problem, the invention according to claim 1 is to measure the tension of a diaphragm for measuring the tension of a diaphragm for a condenser microphone disposed opposite to a fixed pole while being stretched on a support ring. The apparatus includes a drive electrode arranged with a predetermined gap with respect to the diaphragm to be measured, a fiber probe having a light emitting side optical fiber and a light receiving side optical fiber, and non-contact displacement due to vibration of the diaphragm And a voltage amplifier for electrostatically driving the diaphragm by amplifying a predetermined displacement signal of the diaphragm output from the optical displacement detecting means to the drive electrode. When, and a frequency counter for measuring the frequency of the oscillating signal, a fixed electrode having a sound hole for unidirectional condenser microphone unit to the drive electrodes is used The fiber probe is characterized in that it is inserted into the sound hole of the fixed pole.

The invention of claim 2 is characterized in that Oite to the claim 1, the compressor circuit to suppress the amplitude of the displacement signal of the vibration plate in front input stage in a predetermined range of the voltage amplifier is connected .

  According to the first aspect of the present invention, the vibration plate is vibrated by the alternating magnetic field from the drive electrode, and the mechanical displacement of the optical displacement detection means includes a fiber probe having a light projecting side optical fiber and a light receiving side optical fiber. As a result, a loop is formed in which the electric signal (displacement signal) is supplied to the drive electrode through the voltage amplifier, and the diaphragm oscillates continuously. At this time, when the diaphragm tension is high, it oscillates at a high frequency, and when the diaphragm tension is low, it oscillates at a low frequency. Therefore, the diaphragm tension is measured by reading the oscillation frequency with a frequency counter. can do. Therefore, there is no need to manually operate the sweep oscillator as in the conventional example, so there is almost no room for the individual difference in the measured value to intervene, and highly reliable measurement is possible even in an environment where noise exists. It can be carried out.

In addition, by using a fixed electrode with a sound hole for a unidirectional condenser microphone unit as the drive electrode, and inserting a fiber probe into the sound hole of the fixed electrode, the tension of the diaphragm can be adjusted in almost the same state as in actual use. Can be measured.

According to the invention of claim 2 , wherein a compressor circuit that suppresses the amplitude of the displacement signal of the diaphragm within a predetermined range is connected to the stage before the input of the voltage amplifier, the drive electrode is connected between the drive electrode and the diaphragm. Since an excessive signal that causes spark discharge is not applied, the diaphragm can be prevented from being burned out.

  Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2, but the present invention is not limited to this. FIG. 1 is a schematic block diagram showing a configuration of a diaphragm tension measuring apparatus according to the present invention, and FIG. 2 is a schematic cross-sectional view showing a main part of another preferred embodiment of the present invention.

  As shown in FIG. 1, in this tension measuring device, the tension of the diaphragm 11 is measured in the state of a diaphragm unit 10 stretched on a support ring 12. For the diaphragm 11, a synthetic resin film having a metal vapor deposition film or a metal foil is usually used, but is connected to the earth of the device via a support ring 12 in measuring the tension.

  As a basic configuration, the tension measuring device includes a drive electrode 13 disposed opposite to the diaphragm 11 with a predetermined gap, a voltage amplifier (power amplifier) 14 that applies a diaphragm drive voltage to the drive electrode 13, Optical displacement detection means 15 for detecting mechanical displacement associated with vibration of the diaphragm 11 in a non-contact manner, and a frequency for counting the frequency of an electrical signal (displacement signal of the diaphragm 11) output from the optical displacement detection means 15 And a counter 18.

  Note that a fixed electrode (not shown) incorporated in the condenser microphone can be used as the drive electrode 13. That is, the tension of the diaphragm 11 can be measured even in the state of the condenser microphone unit in which the diaphragm 11 and the fixed pole are combined.

  The optical displacement detection means 15 includes a measuring device main body 16 and a fiber probe 17. The measuring device main body 16 includes a light projector 16a made of a light emitting diode or the like and a light receiver 16b made of a photodiode or the like, and an electric signal is output from the light receiver 16b via a predetermined signal processing circuit (not shown). The

  In addition, as this kind of optical displacement detection means 15, as a commercially available thing, the optical fiber type non-contact displacement meter "Optometric OM-10 type (brand name)" by San-Techno Co., Ltd. can be mentioned, for example. .

  The fiber probe 17 includes a light projecting side optical fiber 17a optically connected to the light projecting device 16a and a light receiving side optical fiber 17b optically connected to the light receiving device 16b. Is disposed opposite to the diaphragm 11 on the side opposite to the driving electrode of the diaphragm 11 in a non-contact manner.

  For the sake of drawing, the light projecting side optical fiber 17a and the light receiving side optical fiber 17b are each depicted as one, but in actuality, they are composed of a large number of fiber bundles. Further, the light projecting side optical fiber 17a and the light receiving side optical fiber 17b made of a large number of fiber bundles may be mixed in the same sheath.

  Since the diaphragm 11 is a synthetic resin film having a metal vapor deposition film or a metal foil and has light reflectivity, the light irradiated from the projector 16a through the light projecting side optical fiber 17a is reflected by the diaphragm 11. The reflected light enters the light receiver 16b through the light receiving side optical fiber 17b.

  The amount of light received by the light receiver 16b is proportional to the distance between the tip of the light receiving side optical fiber 17b and the diaphragm 11, that is, the displacement of the diaphragm 11. Therefore, when the diaphragm 11 vibrates, a displacement signal (vibration signal) of the diaphragm 11 is output from the light receiver 16b.

  In this example, the displacement signal of the diaphragm 11 output from the light receiver 16 b is input to the voltage amplifier 14 via the compressor circuit 18. The voltage amplifier 14 applies a displacement signal of the diaphragm 11 to the drive electrode 13 as a predetermined amplified voltage, and generates an alternating magnetic field to drive the diaphragm 11.

  Due to this loop, the diaphragm 11 continuously oscillates. The amplitude condition at that time depends on the amplification degree of the voltage amplifier 14, and the phase condition depends on the acoustic mechanical system of the diaphragm unit 10. Therefore, when the tension of the diaphragm 11 is high, it oscillates at a high frequency, and when the tension of the diaphragm 11 is low, it oscillates at a low frequency.

  Since the displacement signal of the diaphragm 11 output from the light receiver 16b has the above oscillation frequency, the frequency counter 19 counts the frequency of the displacement signal of the diaphragm 11 to determine the tension of the diaphragm 11 by the individual of the measurer. The difference can be measured accurately without intervention.

  In this case, since the displacement signal of the diaphragm 11 reacts only to the displacement of the diaphragm 11 and does not react to the surrounding noise, it can be measured without being interfered by the surrounding noise. Further, since the fiber probe 17 is non-conductive, no electric discharge is generated between the fiber probe 17 and the diaphragm 11. Furthermore, since the diaphragm 11 may be driven with a low alternating voltage, an electric shock accident of the operator can be prevented.

  In the example of FIG. 1, the frequency counter 19 is connected to the input side of the voltage amplifier 14. For example, the frequency counter 19 is connected to the output side of the voltage amplifier 14 or the output side of the measuring instrument body 16 (input side of the compressor circuit 18). May be.

  The compressor circuit 18 is a circuit that suppresses the amplitude of the displacement signal of the diaphragm 11 within a predetermined range, and prevents the diaphragm 11 from being driven with a large amplitude and coming into contact with the drive electrode 13 and being burned out by spark discharge. Is provided.

  Next, another embodiment of the present invention will be described with reference to FIG. In this embodiment, a fixed electrode 13 a for a unidirectional condenser microphone is used as the drive electrode 13.

  Since the fixed pole 13a is provided with a sound hole 13b for allowing sound waves from a rear acoustic terminal (not shown) to act on the back side of the diaphragm 11, the light projecting side optical fiber 17a and the light receiving light are received in the sound hole 13b. The tip of the fiber probe 17 including the side optical fiber 17b is inserted.

  Also in this other embodiment, the tension of the diaphragm 11 is measured in the same manner as in the embodiment of FIG. 1. However, since the tension of the diaphragm 11 is measured on the drive electrode 13 side, The tension of the diaphragm can be measured in substantially the same state as when the unit 10 and the fixed pole 13a are assembled.

The typical block diagram which shows the structure of the tension measuring apparatus of the diaphragm by this invention. The typical sectional view showing the important section of another preferred embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Diaphragm unit 11 Diaphragm 12 Support ring 13 Drive electrode 13a Fixed pole 13b Sound hole 14 Voltage amplifier 15 Optical displacement detection means 16 Measuring instrument main body 16a Light projector 16b Light receiver 17 Fiber probe 17a Light emission side optical fiber 17b Light reception side optical fiber 18 Compressor circuit 19 Frequency counter

Claims (2)

In a tension measuring device for a diaphragm that measures the tension of a diaphragm for a condenser microphone arranged opposite to a fixed pole in a state of being stretched on a support ring,
A non-contact detection of a displacement due to vibration of the diaphragm, including a drive electrode arranged with a predetermined gap with respect to the diaphragm to be measured, a fiber probe having a light emitting side optical fiber and a light receiving side optical fiber An optical displacement detecting means; a voltage amplifier for amplifying the diaphragm displacement signal output from the optical displacement detecting means to give a predetermined amplification to the drive electrode to drive the diaphragm electrostatically; and With a frequency counter that measures the frequency of the vibration signal ,
A diaphragm tension measuring device , wherein a fixed pole having a sound hole for a unidirectional condenser microphone unit is used for the drive electrode, and the fiber probe is inserted through the sound hole of the fixed pole . 2. The diaphragm tension measuring apparatus according to claim 1, wherein a compressor circuit that suppresses an amplitude of a displacement signal of the diaphragm within a predetermined range is connected to an input stage of the voltage amplifier.

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