JP2011071694A - Acoustic resistance value measuring method for acoustic resistance material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for conveniently measuring an acoustic resistance value of an acoustic resistance material which is applied to an electroacoustic transducer, using an easy-to-carry and simple apparatus. <P>SOLUTION: The apparatus includes: a sealing box 10, having an air chamber 11 of a predetermined volume in the inside and an opening 12 formed on a part; a dynamic headphone unit 20 hermetically fitted in the opening 12 with a diaphragm 21 directed toward the inside of the sealing box 10; an AC signal generating section 30 for supplying an AC signal of a predetermined frequency to a voice coil 213 of the diaphragm 21; and a voltage-measuring means 40 for measuring the voltage between both ends of the voice coil 213. An acoustic resistance material 1 to be measured is disposed so as to close the back-surface side of a magnetic circuit 23 of the dynamic headphone unit 20, the AC signal generating section 30 applies an AC signal of a predetermined frequency to the voice coil 213 to vibrate the diaphragm 21; the voltage-measuring means 40 measures the voltage between both the ends of the voice coil 213; and the acoustic resistance value of the acoustic resistance material 1 to be measured is measured, on the basis of the measured voltage. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for measuring an acoustic resistance value of an acoustic resistance material applied to an electric / acoustic transducer such as a microphone unit or a headphone unit. More specifically, the present invention relates to an acoustic resistance material based on the dynamic impedance of a dynamic headphone unit (speaker unit). The present invention relates to a technique for measuring the acoustic resistance value.

  In a microphone unit, a headphone unit, or the like, an acoustic resistance material is used to give sensitivity, frequency response, and directivity to the electric / acoustic converter. In this sense, the acoustic resistance material is one of the important components for the electrical / acoustic transducer.

  Usually, a nylon mesh, a nonwoven fabric, a sponge material having open cells, or the like is used as the acoustic resistance material. Therefore, the acoustic resistance value is measured by measuring the air permeability.

  As an example, in the invention described in Patent Document 1, in the acoustic resistance measurement method for an acoustic resistance material, one end is connected to a compressed air supply source, and a reference acoustic resistance material serving as a reference is disposed at the other end of the tube. In addition, a first pipe having an air constriction part in the middle thereof, one end connected to a compressed air supply source, a sound resistance material to be measured is disposed at the pipe end on the other end side, and an air constriction part is provided in the middle. A second pipe having the same configuration as that of the first pipe including the air resistance value of the air throttling section, a differential pressure gauge, and the first pipe and the second pipe on the downstream side of each air throttling section. And a bridge pipe connected between the two.

  The invention described in Patent Document 1 is regarded as a Wheatstone bridge circuit, and a pipe part including each air throttle part of the first pipe and the second pipe corresponds to a fixed side, and is downstream of the air throttle part of the first pipe. The pipe portion where the reference acoustic resistance material is arranged on the side corresponds to the reference side, and the pipe portion where the measured acoustic resistance material is arranged on the downstream side of the air throttle part of the second pipe corresponds to the measurement side. The pressure gauge corresponds to a galvanometer. Therefore, the acoustic resistance value of the acoustic resistance material to be measured with respect to the reference acoustic resistance material can be measured based on the indication value of the differential pressure gauge.

JP 2005-328347 A

  However, in the above-described conventional example, as a peripheral device, a compressed air supply source (compressor), a pressure regulator (regulator) that adjusts the pressure of the compressed air, and the like are required. Has a problem that it cannot be easily used on a production line.

  Accordingly, an object of the present invention is to make it possible to easily measure the acoustic resistance value of an acoustic resistance material applied to an electric / acoustic transducer with an apparatus that is easy to carry and simple.

  In order to solve the above problems, the present invention provides an acoustic resistance value measuring method for an acoustic resistance material for measuring an acoustic resistance value of an acoustic resistance material applied to an electric / acoustic transducer, wherein an air chamber having a predetermined volume is provided therein. An opening partly formed in a sealed box, a diaphragm having a voice coil, and a magnetic circuit having a magnetic gap in which the voice coil is disposed, and the diaphragm is directed toward the inside of the sealed box. A dynamic headphone unit that is hermetically fitted in the unit, an AC signal generation unit that drives the dynamic headphone unit by applying an AC signal of a predetermined frequency to the voice coil, and measures a voltage across the voice coil. Voltage measuring means, the acoustic resistance material to be measured is arranged so as to close the back side of the magnetic circuit of the dynamic headphone unit, and the AC An AC signal having a predetermined frequency is applied to the voice coil from a signal generator to vibrate the diaphragm, and the voltage across the voice coil is measured by the voltage measuring means, and the measured sound is measured based on the measured voltage. The acoustic resistance value of the resistance material is measured.

  In the present invention, the frequency of the AC signal applied to the voice coil is set to the resonance frequency of the diaphragm at the time of no load when the acoustic resistance material to be measured is removed from the back side of the magnetic circuit of the dynamic headphone unit. preferable.

  According to a preferred aspect of the present invention, an air passage is formed in the magnetic circuit from the atmosphere side to the back side of the diaphragm.

  According to a preferred aspect of the present invention, the dynamic headphone unit includes a unit frame that supports a peripheral portion of the diaphragm and the magnetic circuit, and the unit frame is airtightly fitted into the opening. At the same time, a cylindrical portion that supports the magnetic circuit of the unit frame protrudes from the back surface of the magnetic circuit, and the acoustic resistance material to be measured is disposed on an end surface of the cylindrical portion.

  According to the present invention, since the acoustic resistance value of the acoustic resistance material to be measured can be measured using the sealed box having the dynamic headphone unit, the AC signal generating unit, and the voltage measuring means as the basic components, it is brought into a production line or the like. Is easy, and the measurement operation can be performed easily.

The perspective view which shows the acoustic resistance material of a measuring object. Sectional drawing which shows one Embodiment of the acoustic resistance value measuring method of the acoustic resistance material by this invention. The circuit diagram which shows the electrical measurement system of this invention. The graph which shows the example of a measurement of an acoustic resistance value.

  Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 4, but the present invention is not limited to this.

  First, FIG. 1 shows a measured acoustic resistance material 1 whose acoustic resistance value is measured according to the present invention. The acoustic resistance material 1 to be measured is made of a nylon mesh, a nonwoven fabric, a sponge material having open cells, or the like. The acoustic resistance material 1 to be measured may be a mother-like large size from which individual acoustic resistance materials are cut out, or may be in any form that is actually attached to a sound wave path such as a microphone.

  In order to measure the acoustic resistance value of the acoustic resistance material 1 to be measured, the sealed box 10 and the dynamic headphone unit 20 shown in FIG. 2, and the AC signal generator 30 and the voltage measuring means 40 shown in FIG. 3 are used.

  The sealed box 10 is a box having an air chamber 11 of a predetermined volume inside, and is provided with an opening 12 into which a dynamic headphone unit 20 is fitted in an airtight manner.

  The dynamic headphone unit 20 includes a diaphragm 21, a magnetic circuit 23, and a unit frame 25 that supports them. The dynamic headphone unit 20 may be referred to as a speaker unit.

  The diaphragm 21 includes a center dome 211 and a sub dome 212 integrally formed around the center dome 211, and the entirety thereof is formed of a synthetic resin thin film. A voice coil 213 is fixed to the boundary portion between the center dome 211 and the sub dome 212 on the back side of the diaphragm 21 (upper side in FIG. 2) via an adhesive.

  The magnetic circuit 23 includes a yoke 231 formed in a cup shape, a disk-shaped permanent magnet 232 attached to the bottom of the yoke 231, and a similarly disk-shaped pole piece 233 disposed on the permanent magnet 232. A magnetic gap is formed between the yoke 231 and the pole piece 233.

  The unit frame 25 includes a cylindrical portion 251 and a disk-shaped flange portion 252 that is connected to one end 251a side (the lower end side in FIG. 2) of the cylindrical portion 251.

  The magnetic circuit 23 is supported in the cylindrical portion 251, and the peripheral edge of the sub dome 212 is supported by the flange portion 252, so that the voice coil 213 is disposed in the magnetic gap of the magnetic circuit 23 so as to vibrate.

  The dynamic headphone unit 20 assembled in this way is airtightly fitted into the opening 12 of the sealed box 10 so that the diaphragm 21 faces the air chamber 11.

  In this embodiment, an air passage 234 communicating from the free space (atmosphere) side to the back side of the diaphragm 21 is formed in the central portion of the yoke 231, the permanent magnet 232, and the pole piece 233 of the magnetic circuit 23.

  Note that the other end 251b side (upper end side in FIG. 2) of the cylindrical portion 251 protrudes from the back surface (yoke 231) of the magnetic circuit 23, and is measured on the other end 251b side of the cylindrical portion 251 during acoustic resistance measurement. An acoustic resistance material 1 is disposed.

  At that time, in the acoustic resistance material 1 to be measured having a high acoustic resistance value, it is preferable to seal the peripheral end face with, for example, a film material so that air does not leak from the peripheral end face side.

  Referring to FIG. 3, AC signal generation unit 30 is connected to voice coil 213 through supply resistor Rs. In this example, the output voltage of the AC signal generator 30 is constant at 6V (effective value), the supply resistance Rs is 1 KΩ, and the resistance value of the voice coil 213 is 32Ω.

  The voltage measuring means 40 measures the voltage across the voice coil 213. In this embodiment, an analog level meter is used. For example, a digital voltage measuring device having a level determination function is used. Also good.

  Next, a method for measuring the tension of the acoustic resistance material 1 to be measured will be described. In the present invention, the acoustic resistance value of the acoustic resistance material 1 to be measured is measured by measuring the dynamic impedance of the dynamic headphone unit 20.

  When the diaphragm 21 vibrates, dynamic impedance is generated in addition to the DC resistance and inductance of the voice coil 213. That is, the dynamic impedance increases as the amplitude (vibration speed) of the diaphragm 21 increases, and accordingly, the voltage (signal level) across the voice coil 213 increases. Incidentally, when the voice coil 213 is fixed with a finger or the like, only the DC resistance and the inductance are obtained.

  When the acoustic resistance material 1 to be measured is not attached to the measuring apparatus of FIG. 2, the dynamic headphone unit 20 is driven by sweeping the frequency of the AC signal of the AC signal generator 30 to vibrate the diaphragm 21. Then, in this example, the resonance peak of the diaphragm 21 in which the voltage across the voice coil 213 becomes maximum appears around 150 Hz (see the waveform W1 in FIG. 4).

  Therefore, when measuring the acoustic resistance of the acoustic resistance material 1 to be measured, the frequency of the AC signal of the AC signal generating unit 30 is fixed to 150 Hz, for example.

  Then, the acoustic resistance material 1 to be measured is disposed at the other end 251b of the cylindrical portion 251 of the unit frame 25, and the dynamic headphone unit 20 is driven by the AC signal from the AC signal generating unit 30 to vibrate the diaphragm 21, and the level. A voltage (dynamic impedance) across the voice coil 213 is measured by a meter (voltage measuring means) 40.

  When the acoustic resistance value of the acoustic resistance material 1 to be measured is low, the diaphragm 21 is likely to vibrate, and accordingly, the dynamic impedance increases and the voltage across the voice coil 213 increases. In FIG. 4, the W3 of the two-dot chain line shown in the figure is the waveform observed at this time, and the voltage VH across the voice coil 213 at 150 Hz is about 520 mV.

  On the other hand, when the acoustic resistance value of the acoustic resistance material 1 to be measured is high, the diaphragm 21 is less likely to vibrate. Accordingly, the dynamic impedance is lowered and the voltage across the voice coil 213 is reduced. Lower. In FIG. 4, W4 of the illustrated chain line is a waveform observed at this time, and the voltage VL across the voice coil 213 at 150 Hz is about 320 mV.

  In FIG. 4, a waveform W2 shown by a solid line in FIG. 4 is an observation waveform using an acoustic resistance material whose acoustic resistance value, which has been determined to be good in advance, is known, and the voltage Vref between both ends of the voice coil 213 at 150 Hz is about 410 mV. Yes.

  Thus, according to the present invention, the acoustic resistance value of the acoustic resistance material 1 to be measured can be measured by the voltage across the voice coil 213, that is, the dynamic impedance of the dynamic headphone unit 20.

  In an actual work site, for example, a threshold (upper limit value and lower limit value) of a predetermined width is set with reference to the voltage Vref across the voice coil 213 obtained from a good acoustic resistance material, and the acoustic resistance material 1 to be measured is If the resistance value is within the threshold value, the determination is “good”, and if the resistance value is outside the threshold value, the determination is “bad”.

DESCRIPTION OF SYMBOLS 1 Measured acoustic resistance material 10 Sealed box 11 Air chamber 12 Opening 20 Dynamic headphone unit (speaker unit)
DESCRIPTION OF SYMBOLS 21 Diaphragm 213 Voice coil 23 Magnetic circuit 231 Yoke 232 Permanent magnet 233 Pole piece 234 Air passage 30 AC signal generation part 40 Voltage measurement means

Claims (4)

In the acoustic resistance value measuring method for an acoustic resistance material for measuring the acoustic resistance value of an acoustic resistance material applied to an electrical / acoustic transducer,
The diaphragm includes a sealed box having an air chamber of a predetermined volume and having an opening formed in a part thereof, a diaphragm having a voice coil, and a magnetic circuit having a magnetic gap in which the voice coil is disposed. A dynamic headphone unit that is airtightly fitted into the opening toward the inside of the sealed box, an AC signal generator that drives the dynamic headphone unit by applying an AC signal of a predetermined frequency to the voice coil, and Voltage measuring means for measuring the voltage across the voice coil,
The acoustic resistance material to be measured is disposed so as to block the back side of the magnetic circuit of the dynamic headphone unit, and an AC signal having a predetermined frequency is applied to the voice coil from the AC signal generator to vibrate the diaphragm, A method for measuring an acoustic resistance value of an acoustic resistance material, comprising: measuring a voltage between both ends of the voice coil by a voltage measuring means; and measuring an acoustic resistance value of the acoustic resistance material to be measured based on the measured voltage.   The frequency of the AC signal applied to the voice coil is a resonance frequency of the diaphragm at the time of no load when the acoustic resistance material to be measured is removed from the back side of the magnetic circuit of the dynamic headphone unit. Item 2. A method for measuring an acoustic resistance value of the acoustic resistance material according to Item 1.   The method for measuring an acoustic resistance value of an acoustic resistance material according to claim 1 or 2, wherein an air passage is formed in the magnetic circuit from the atmosphere side to the back side of the diaphragm.   The dynamic headphone unit includes a unit frame that supports a peripheral portion of the diaphragm and the magnetic circuit, and the unit frame is hermetically fitted into the opening and supports the magnetic circuit of the unit frame. 4. The acoustic device according to claim 1, wherein a cylindrical portion that protrudes from a back surface of the magnetic circuit, and the acoustic resistance material to be measured is disposed on an end surface of the cylindrical portion. 5. A method for measuring an acoustic resistance value of a resistance material.

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