Measurement of resonance frequency and loss factor of a microphone diaphragm using a laser vibrometer |
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Authors: | Jae Gap Suh,Hack-Yoon Kim,Suzuki Yô iti |
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Affiliation: | a Division of Physical Metrology, Korea Research Institute of Standards and Science, 1 Doryong-Dong Yuseong-Gu, Daejeon 305-340, Republic of Korea b Department of Electronic Engineering, Cheongju University, 36 Naeduk-Dong, Cheongju, Republic of Korea c Research Institute of Electrical Communication, Tohoku University, Katahira 2-1-1, Aoba-Ku, Sandai 980-8577, Japan |
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Abstract: | The pressure sensitivity of a laboratory standard microphone is determined using a reciprocity technique that measures the electrical transfer impedance of two microphones connected acoustically by a coupler. The electrical transfer impedance is a function of the coupler volume and the equivalent volumes of the microphones. The equivalent volume given as a function of the frequency can be determined in experiments or can be calculated if the equivalent volume at a low frequency as well as the resonance frequency and loss factor of the microphone diaphragm are known. Therefore, it is necessary to determine the resonance frequency and the loss factor accurately to obtain an accurate reading of the pressure sensitivity.In this paper, a new method to determine the resonance frequency and loss factor of a microphone diaphragm is proposed. The frequency response of the diaphragm displacement is measured by a laser vibrometer and the part of the response near the resonance frequency is used to determine the microphone parameters via least square fitting with the equation of a vibration model with one degree-of-freedom. Since the values measured by this method are close to the nominal values and the repeatability is highly feasible, the proposed method will be useful to determine the resonance frequency and loss factor of a microphone diaphragm. |
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Keywords: | Resonance frequency Loss factor Least square fitting Microphone diaphragm Laser vibrometer |
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