Audio Engineering Society
Chicago
Meeting Review, April 16, 2008
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4/16/08 Meeting Highlights A combination Boundary Element (BE)/ Analytical solver has been developed to simulate the response of both an omnidirectional and a unidirectional condenser microphone capsule.� This method is an improvement over traditional lumped element methods because the spatially dependent acoustical and mechanical components do not need to be approximated to one dimension.�� The calculation approach was described from a system perspective.� The capsule is comprised or four components having coupled responses.� The external surface pressure (with or without a port for omni/uni directionality) is modeled using the BE method.� The diaphragm displacement, diaphragm/backplate air-film pressure, and back chamber pressure are modeled using the analytical modal solution.� The BE mesh of the solid model is generated using commercial CAD software, and the response is simulated with custom C++ program. The frequency response to a free-field point source is calculated, and the spatial behavior of the diaphragm is animated.� Comparing measured and simulated results of a prototype, initial attempts were good but there was deviation of a few dB in the frequency response above about 7 kHz.� And in the unidirectional case, the off-axis directionality was off.� Mr. Grinnip explained how he was able to improve the results when he considered the temperature profile inside the cavities, and this led to several questions.� Both simulated and measured (with a laser vibrometer) animations of the diaphragm displacement at 5 kHz were shown to have excellent agreement. A
healthy question and answer session concluded the meeting.� Topics included alternative methods for
solving the matrix equation, simulating the self-noise,
and expected results when various parameters are manipulated.
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