| http://www.w3.org/ns/prov#value | - Apparatus according to claim 12 wherein said microphone is a condenser microphone which has a pair of diaphragms acting as a capacitor, housing means for sound isolating one of said diaphragms, low pass filter means in said housing means for equilibrating balloon pressure changes, and means for equalizing pressure on both sides of said one diaphragm.
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