JP2009192413A - Method of measuring diaphragm tension and its device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a diaphragm tension more easily while removing dusts on a diaphragm. <P>SOLUTION: Tension of a diaphragm 10 for an electrostatic microphone disposed to face a fixed pole is measured under a condition stretched over a support ring 11, in which the diaphragm 10 is vibrated by blowing compressed air from an air nozzle 21 to the diaphragm 10 stretched over the support ring 11 to generate a vibrating sound, the vibrating sound is picked up by a measurement microphone 22, an electric signal output from the measurement microphone 22 is input to a spectrum analyzer 23 to wave-analyze, and the tension of the diaphragm 10 is measured based on the frequency of the vibrating sound. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for measuring the tension of a diaphragm used in a condenser microphone. More specifically, the present invention relates to a technique for measuring the tension of a diaphragm by vibrating the diaphragm with compressed air.

  Condenser microphones are equipped with electrostatic acoustoelectric transducers that have a diaphragm and a fixed pole that vibrate in response to sound waves, but are of primary sound pressure gradient type (unidirectional) In some cases, the lower limit and the adsorption stability with respect to the fixed pole depend on the tension of the diaphragm.

  For this reason, it is necessary to reduce the variation in the tension of the diaphragm in order to make the performance 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 example, for a diaphragm unit for general-purpose condenser microphones, individual tension measurement is generally not performed. However, in the case of a condenser microphone for studios where sound quality is particularly important, individual units with high performance and sound quality are required. The difference is required to be small (the tolerance of individual difference is generally specified within 10%).

  The method of measuring the tension of the diaphragm is roughly divided into a method of measuring the amplitude by vibrating the diaphragm with sound waves, a method of detecting the level of sound waves radiated at that time by vibrating the diaphragm with an alternating magnetic field, and In any of the 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.

  In view of this, the applicant of Patent Document 1 outputs a drive electrode arranged with a predetermined gap with respect to the diaphragm, a measurement microphone that collects sound waves radiated from the diaphragm, and a measurement microphone. A diaphragm having a voltage amplifier that amplifies a microphone output signal to be applied to the drive electrode and electrostatically drives the diaphragm, and a frequency counter that measures the frequency of the microphone output signal, thereby continuously maintaining the diaphragm. It was proposed to oscillate and to measure the tension of the diaphragm by counting the oscillation frequency at that time with a frequency counter.

JP 2006-98277 A

  According to the invention described in Patent Document 1, since the diaphragm is continuously oscillated and the tension of the diaphragm is measured at the oscillation frequency at that time, the tension of the diaphragm can be measured with high reliability. Can be measured.

  However, as a work problem, it is necessary to accurately set the diaphragm unit on the measurement table so as not to cause a measurement error, which takes time and labor. Further, since the metal vapor deposition film is formed on the surface opposite to the surface facing the fixed pole on the diaphragm, dust easily adheres to the surface facing the fixed pole due to static electricity or the like. If the measurement is performed with dust attached, a measurement error may occur.

  Accordingly, an object of the present invention is to make it possible to more easily measure the tension of the diaphragm while removing dust adhering to the diaphragm.

  The present invention has been made by paying attention to the fact that when the compressed air is partially blown against the diaphragm, a vibration sound depending on the tension is generated. The invention according to claim 1 is applied to the support ring. In the tension measuring method of the diaphragm for measuring the tension of the diaphragm for the condenser microphone disposed opposite to the fixed pole in a stretched state, with respect to the diaphragm stretched on the support ring, The compressed air is blown from the air nozzle to vibrate the diaphragm to generate a vibration sound, the vibration sound is picked up by the measurement microphone, and the electric signal output from the measurement microphone is input to the spectrum analyzer. And analyzing the waveform and measuring the tension of the diaphragm based on the frequency of the vibration sound.

  A second aspect of the present invention is characterized in that, in the first aspect, the compressed air is blown to a surface side of the diaphragm on which the metal vapor deposition film is not formed.

  Invention of Claim 3 sprays the compressed air which ejects from the said air nozzle in the Claim 1 or 2 toward the position away from the diagonal direction with respect to the said diaphragm, and the center of the said diaphragm. It is characterized by that.

  According to a fourth aspect of the present invention, there is provided a diaphragm tension measuring apparatus for measuring the tension of a diaphragm for a condenser microphone disposed opposite to a fixed pole while being stretched on a support ring. An air nozzle that blows compressed air against the diaphragm stretched on a ring, a measurement microphone that measures vibration sound generated from the diaphragm by blowing the compressed air, and an output from the measurement microphone And a spectrum analyzer for analyzing the waveform of the electric signal to be generated.

  According to the first aspect of the present invention, the compressed air may be blown from the air nozzle to the diaphragm, and the diaphragm may be vibrated to generate vibration sound. Is not necessary, and the tension of the diaphragm can be measured more easily. The present invention is most suitable for a general-purpose model in which, for example, the required tension range only needs to be within 20%.

  According to the second aspect of the present invention, dust attached to the diaphragm is removed by blowing the compressed air to the surface side of the diaphragm where the metal vapor deposition film is not formed. Can be measured more accurately.

  According to the invention described in claim 3, by blowing the compressed air ejected from the air nozzle in an oblique direction to the diaphragm and toward a position away from the center of the diaphragm, a relatively large vibration noise is generated. Is obtained.

  Next, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram showing a diaphragm tension measuring apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the diaphragm 10 is placed on the measurement table 12 while being stretched on the support ring 11. A metal washer-like ring is used for the support ring 11.

  The diaphragm 10 is made of a synthetic resin thin film, and a metal vapor deposition film (not shown) is formed on one surface 10b on the side attached to the support ring 11, and the other surface 10a on the opposite side is not shown. On the surface facing the fixed pole, the diaphragm 10 is placed on the measuring table 12 so that it can freely vibrate with the other surface 10a up.

  The present invention focuses on the fact that when compressed air is blown onto a part of the diaphragm 10, the diaphragm 10 vibrates at a frequency depending on the tension to generate vibration sound (sound wave). The measurement system 20 includes the following components.

  An air nozzle 21 that blows compressed air on the diaphragm 10, a measurement microphone 22 that collects vibration sound generated from the diaphragm 10, and an electrical signal output from the measurement microphone 22 is subjected to waveform analysis by FFT, for example. And a spectrum analyzer 23.

  The air nozzle 21 is connected to a compressed air supply source such as an air compressor (not shown). The inner diameter of the air nozzle 21 is preferably about 0.8 mm. The air pressure of the compressed air is kept constant.

  In blowing compressed air onto the surface 10 a of the diaphragm 10, as shown in FIG. 1, the air nozzle 21 is inclined by about 30 to 45 °, for example, with respect to the diaphragm 10, and the compressed air is inclined with respect to the diaphragm 10 from an oblique direction. In addition, it is preferable to spray toward a position slightly away from the center of the diaphragm 10 (preferably, a position about 30% in the radial direction from the center). Thereby, a comparatively loud vibration sound is obtained.

  The measurement microphone 22 is preferably disposed directly below the diaphragm 10 on the surface 10 b side of the diaphragm 10. The measurement microphone 22 is preferably an omnidirectional microphone that has a flat frequency response and a very small phase rotation in the voice band to be used as compared to other microphones.

  The spectrum analyzer 23 may be a commercially available product. On the display screen 23a of the spectrum analyzer 23, an analysis waveform is displayed with the horizontal axis representing frequency and the vertical axis representing level.

  In order to measure the tension of the diaphragm 1, compressed air is blown from the air nozzle 21 to the diaphragm 10 to vibrate the diaphragm 10 to generate vibration sound. The vibration sound is picked up by the measurement microphone 22 and converted into an electric signal. The electric signal is input to the spectrum analyzer 23.

  As a result, the frequency of the vibration sound is displayed on the display screen 23 a of the spectrum analyzer 23. Since the frequency of the vibration sound depends on the tension of the diaphragm 10, the tension of the diaphragm 10 can be measured by reading the frequency.

  According to the present invention, dust attached to the surface 10a of the diaphragm 10 is removed by blowing compressed air, so that more accurate measurement can be performed. In addition, by providing the display window 23a with a threshold window 23b having an allowable frequency range, it is possible to easily determine whether the product is good or defective.

The schematic diagram which shows the tension measuring apparatus of the diaphragm which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Diaphragm 11 Support ring 20 Measurement system 21 Air nozzle 22 Microphone for measurement 23 Spectrum analyzer

Claims (4)

In the tension measurement method of the diaphragm for measuring the tension of the diaphragm for the condenser microphone arranged opposite to the fixed pole in a state of being stretched on the support ring,
With respect to the diaphragm stretched on the support ring, compressed air is blown from an air nozzle to vibrate the diaphragm to generate a vibration sound, and the vibration sound is collected by a measurement microphone, A method for measuring a tension of a diaphragm, comprising: inputting an electric signal output from the measurement microphone to a spectrum analyzer to analyze a waveform; and measuring a tension of the diaphragm based on a frequency of the vibration sound.   2. The method of measuring a tension of a diaphragm according to claim 1, wherein the compressed air is blown to a surface of the diaphragm where a metal vapor deposition film is not formed.   3. The diaphragm according to claim 1, wherein the compressed air ejected from the air nozzle is blown from an oblique direction to the diaphragm and toward a position away from the center of the diaphragm. 4. Tension measurement method. 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,
An air nozzle that blows compressed air against the diaphragm stretched on the support ring, a measurement microphone that measures vibration sound generated from the diaphragm by blowing the compressed air, and the measurement microphone A diaphragm tension measuring apparatus comprising: a spectrum analyzer that analyzes a waveform of an electric signal output from the diaphragm.

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