Patent ID: 7408109

Claim:
Apparatus comprising a capacitive vibration-sensitive electrical transducer having, in combination: a. sensor means comprising a fixed variable capacitor plate further comprising an electrically conductive surface facing, placed inside, and separated from an electrically conductive cavity integrated into an acoustic musical instrument, where said electrically conductive cavity substantially comprises, in whole or in part, a vibrating surface on said acoustic musical instrument that, through its vibration, emits a substantial portion of the sound waves that characterize the sound of said musical instrument to an external listener, and where said electrically conductive cavity is free to vibrate in unison with said vibrating surface wherever said electrically conductive cavity and said vibrating surface make physical contact; b. input and output means comprising an electric circuit, to be placed inside said electrically conductive cavity to benefit from said cavity's electromagnetic shielding properties, where said electric circuit further comprises: an audio signal AC preamplifier circuit, means to connect said electric circuit to a source of electrical power, means to connect said electrically conducting cavity to a source of electrical grounding, and means to connect said fixed variable capacitor plate to a non-oscillating electrical voltage, differing from that of the electrically conducting cavity, through a source of electrical resistance great enough to permit substantial AC voltage fluctuations at audio frequencies to occur in said fixed variable capacitor plate when said electrically conducting cavity oscillates at said audio frequencies proportional to the voltage difference existing between said fixed variable capacitor plate and said electrically conducting cavity, where said AC voltage fluctuations comprise the signal input to said audio signal AC preamplifier circuit, and; c. means to filter the audio signal AC preamplifier output signal bandwidth and modify the output impedance of said audio signal AC preamplifier to make said audio signal AC preamplifier output signal compatible with the AC output signal of microphones or magnetic pickup devices, and further comprising means to make said audio signal AC preamplifier output available to microphone or instrument signal inputs found on audio recording and amplification equipment; whereby said apparatus is used to reproduce the sound of said acoustic musical instrument as an electrical signal compatible with the signals generated by microphones, magnetic pickups, and other sources of audio signals used for musical recording and amplification purposes.