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US 5,473,684 AGranted
Noise-canceling differential microphone assembly
AssigneeAT&T Corp.
InventorsCharles S. Bartlett, Michael A. Zuniga
Life of this patent
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Abstract
Improved microphone performance is achieved by configuring a second-order derivative microphone assembly in such a way that radially divergent near-field input produces a microphone response proportional to a first-order spatial derivative of the acoustic pressure field.
Claims20
Apparatus comprising a transducer for converting acoustic signals, emitted by a source, to electrical output signals in the presence of acoustic noise;
- and further comprising a platform for maintaining the transducer at a substantially constant distance from the source;
- wherein the transducer is adapted to respond to a second-order spatial derivative of the pressure field associated with at least some acoustic fields, CHARACTERIZED IN THAT the transducer comprises:
- a) two first-order differential microphones separated by a distance d, the microphones so situated within the platform that in use, they are on the same side of the source and approximately equidistant therefrom, and each microphone including a membrane having a substantially perpendicular orientation relative to a straight line drawn between the two microphones;
- and
- b) differencing means for receiving an electrical output signal from each of the two microphones, and for producing, in response thereto, an electrical difference signal proportional to the difference between the respective microphone output signals.
2 more elements
Apparatus comprising a transducer for converting acoustic signals, emitted by a source, to electrical output signals in the presence of acoustic noise;
- and further comprising a platform for maintaining the transducer at a substantially constant distance from the source along an axis to be referred to as the major axis;
- wherein the transducer is adapted to respond to a second-order spatial derivative of the pressure field associated with at least some acoustic fields, CHARACTERIZED IN THAT
- a) the transducer comprises means for sensing the pressure field at respective first and second locations separated at least along a minor axis perpendicular to the major axis;
- b) the sensing means are adapted to produce first and second output signals proportional to the first spatial derivative of the pressure field, along the minor axis, at the first and second locations, respectively;
- c) the transducer further comprises means for combining the first and second output signals into a net output signal representing the difference between the first and second output signals;
- and
- d) the first and second locations are so chosen that radially divergent acoustic signals emitted by the source contribute, to the net output signal, mutually reinforcing first and second output signals that are proportional to the first spatial derivative of the pressure field along the minor axis.
4 more elements
A method for converting acoustic signals, emitted by a source, to electrical output signals in the presence of far-field acoustic noise, the method comprising the steps of:
- a) sensing an acoustic pressure field at respective first and second locations;
- b) producing first and second electrical output signals, each said output signal proportional to a first spatial derivative of the pressure field at a respective one of said locations;
- and
- c) combining the first and second output signals into a net output signal representing the difference between the first and second output signals, such that the net output signal is approximately proportional to a second-order spatial derivative of the pressure field at a point intermediate the first and second locations, said point separated from said source along an axis to be referred to as the major axis;
- CHARACTERIZED IN THAT:
- d) the first and second locations are separated at least along a minor axis perpendicular to the major axis;
- e) the sensing step is carried out such that each of the resulting first and second output signals is proportional to the first derivative of the pressure field along the minor axis, and the net output signal is approximately proportional to the second spatial derivative of the pressure field along the minor axis;
- and
- f) the first and second locations are so chosen that radially divergent acoustic signals emitted by the source contribute, to the net output signal, mutually reinforcing first and second output signals that are proportional to the first spatial derivative of the pressure field along the minor axis.
6 more elements
Dependencies are inferred from the claim text.