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In a reply to the thread titled "Top secret Earthworks M50 capsule..." I suggested that the low frequency response of?an omnidirectional microphone can be tested by placing the microphone can be tested by placing the microphone inside a small enclosure. It may not be immediately obvious?but the pressure inside a sealed loudspeaker enclosure is very uniform at frequencies below the loudspeaker resonance.When I say uniform, I mean that it is flat from the resonant frequency down to DC. The practical low frequency limit is determined by the time constant of any leaks. The surround of the woofer needs to be rubber. Cloth surrounds leak. Such a test enclosure can also be used to test the distortion and overload performance of microphones because such a system is extremely efficient. Assume that the volume?displacement is perhaps .1 %. Nominal air pressure is about 101,325 Pascals.If the woofer compresses the air by .1% then that change is 100 Pascals which is 134 dBSPL. That back of the envelope?calculation shows that the sound pressure level inside a woofer enclosure can reach extremely high levels. I've been using this technique for about fifty years and it works extremely well. But for omnis only. AN5-MicroMeasChamber-Rev4Eng.pdf
AN5-MicroMeasChamber-Rev4Eng.pdf
Acoustic coupler.pdf
Acoustic coupler.pdf
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