Method and apparatus for attentuating external origin noise reaching the eardrum, and for improving intelligibility of electro-acoustic communications

  • US 4,833,719 A
  • Filed: 09/23/1987
  • Issued: 05/23/1989
  • Est. Priority Date: 03/07/1986
  • Status: Expired due to Term
First Claim
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1. Apparatus for attenuating externally originating noise reaching the eardrum, the apparatus being of the type including passive soundproofing means which together with each ear delimits a respective cavity, and also including an electro-acoustic transducer and a microphone disposed inside each said cavity and interconnected via a feedback loop including a constant gain amplifier and a filter with which they constitute an active sound attenuator, the apparatus being characterized in that the transfer function C(w) of said filter is a complex polynomial function and in that the product of the constant gain K of said amplifier multiplied by the modulus |C(w)| of the transfer function of said filter and by the modulus |H(w)| of the open loop transfer function as measured at the input to said transducer and at the output from said microphone is considerably greater than unity throughout the range of low audio frequencies which are to be attenuated and satisfies the stability criterion for all audible frequencies.

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