| 摘要 |
Active noise control systems that heretofore have had at least a microphone which responds to ambient acoustic noise waves and a speaker which transmits an altered version of the ambient noise waves over a frequency range to provide a measure of noise cancellation in the region of the microphone are improved by using a bilateral transducer circuit in place of a separate microphone and speaker. Two embodiments of such ANC systems are disclosed. Three embodiments of a bilateral transducer circuit are disclosed, and in each a bilateral transducer both senses ambient noise and produces acoustic waves to cancel the noise. The electrical interface for each bilateral transducer circuit consists of a speaker input drive signal as an input and a simulated microphone signal as an output. In a first embodiment the drive to the bilateral transducer is periodically turned off at a rate above the hearing frequency limit, and in the "off period" the transducer's drive element is sensed to produce a reverse output signal from which is subtracted a synthesized signal representing the speaker velocity response to the drive signal to produce the simulated microphone signal which is then processed in further active noise circuitry in a known way. In further embodiments the reverse output signal is derived by sensing the energy being sent to the transducer to produce the acoustic waves, or by a separate sensing coil in a coil driven transducer. |
