Method and apparatus for attentuating external origin noise reaching the eardrum, and for improving intelligibility of electro-acoustic communications
DCFirst Claim
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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Abstract
The invention relates to a method and to apparatus for attenuating externally originating noise reaching the eardrum while still enabling communication via an electro-acoustic path. Apparatus according to the invention comprises passive attenuation means disposed about each ear and delimiting a cavity (10). In addition it includes active attenuation means comprising a loudspeaker (6) placed inside the cavity (10) and a microphone (8) placed in the external ear duct or at the inlet thereto, said loudspeaker and microphone being interconnected by a constant gain amplifier (11) and an active analog filter (12) of the polynomial type, with the passive components thereof being designed to provide a given transfer function. One application lies in the construction of protective headsets fitted with incorporated loudspeakers enabling electro-acoustic communication.
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Citations
19 Claims
- 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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7. A method of attenuating external origin noise reaching the eardrum, comprising the following steps:
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placing around each ear a passive soundproofing means which, together with the ear, delimits a cavity; placing in each of said cavities an electro-acoustic transducer and a microphone; electrically interconnecting said microphone and said transducer by an electronic feedback loop comprising a constant gain amplifier and a filter having a transfer function which is a complex polynomial function; measuring the open loop transfer function H(w) of the assembly constituted by the transducer, the microphone and said cavity; and calculating the coefficients of said polynomial function so that the product of the constant gain of said amplifier multiplied by the modulus of said open loop transfer function and by the modulus of the transfer function of said filter is much greater than unity over the range of low frequencies where said passive soundproofing means is of low effectiveness. - View Dependent Claims (8, 9, 10)
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11. A method of attenuating external origin noise reaching the eardrum, comprising the following steps:
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placing around each ear passive soundproofing means which, together with the ear, delimits a cavity; placing in each of said cavities an electro-acoustic transducer and a microphone; electrically interconnecting said microphone and said transducer by an electronic feedback loop comprising a constant gain amplifier and a filter having a transfer function which is a complex polynomial function; temporarily disconnecting said microphone from said transducer, applying an electric signal corresponding to white noise to the input of said transducer and measuring the open loop transfer function H(w) of the assembly constituted by said transducer, said microphone and said cavity by means of a spectrum analyzer which simultaneously receives said electrical signal and the electric signal emitted by said microphone; and calculating the coefficients of said polynomial function so that the product of the constant gain of said amplifier multiplied by the modulus of said open loop transfer function and by the modulus of the transfer function of said filter is much greater than unity over the range of low frequencies where said passive soundproofing means is of low effectiveness. - View Dependent Claims (12, 13, 14, 15)
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16. Apparatus for attenuating external origin noise reaching the eardrum comprising passive soundproofing means surrounding each ear which delimits with each ear a cavity, and further comprising an electro-acoustic transducer and a microphone which are disposed in each of said cavities and which are electrically interconnected via an electronic feedback loop including a constant gain amplifier and filter means having a complex polynomial transfer function wherein the product of the constant gain of said amplifier multiplied by the modulus of said transfer function of said filter means and by the modulus of the open loop transfer function measured between the input electric signal to said transducer and the output electric signal from said microphone is much greater than unity over the range of low audio frequencies and wherein said filter means comprises a plurality of analog filters of the low pass, band-pass and high pass types which are connected in parallel and have the same cut-off frequency and the same Q factor.
- 17. Apparatus for attenuating external origin noise reaching the eardrum comprising passive soundproofing means surrounding each ear which delimits with each ear a cavity, and further comprising an electro-acoustic transducer and a microphone which are disposed in each of said cavities and which are electrically interconnected via an electronic feedback loop including a constant gain amplifier and filter means having a complex polynomial transfer function wherein the product of the constant gain of said amplifier multiplied by the modulus of said transfer function of said filter means and by the modulus of the open loop transfer function measured between the input electric signal to said transducer and the output electric signal from said microphone is much greater than unity over the range of low audio frequencies, and wherein said filter means comprises one or more analog filters of the band-pass type or of the band-pass and low pass type which are connected in parallel, which have a transfer function suitable for avoiding instabilities in the zone where the modulus is greatest.
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19. Apparatus for attenuating external origin noise reaching the eardrum comprising passive soundproofing means surrounding each ear which delimits with each ear a cavity, and further comprising an electro-acoustic transducer and a microphone which are disposed in each of said cavities and which are electrically interconnected via an electronic feedback loop including a constant gain amplifier and filter means having a complex polynomial transfer function wherein the product of the constant gain of said amplifier multiplied by the modulus of said transfer function of said filter means and by the modulus of the open loop transfer function measured between the input electric signal to said transducer and the output electric signal from said microphone is much greater than unity over the range of low audio frequencies and wherein the gain of said amplifier is positive and the transfer function of said filter means is determined such that the phase of said transfer function does not pass through the value zero in the pass-band of said filter means.
Specification