System and method of microphone placement for noise attenuation
A method and system for attenuating noise comprises identifying a location in an area at which sound emitted from one or more speakers has acoustic characteristics that are substantially similar in measure to corresponding acoustic characteristics of the emitted sound at a location approximated to be near an ear of an occupant of the area. A microphone, which may be a virtual microphone, is disposed at the identified location. The microphone detects sound at the identified location. In response to the sound detected by the microphone, the one or more speakers emit a noise-canceling audio signal adapted to attenuate one or more frequencies in the sound detected by the microphone.
1. A method of attenuating noise comprising:
identifying a location in an area at which sound emitted from one or more speakers has acoustic characteristics that are matched in measure to corresponding acoustic characteristics of the emitted sound at a location near an ear of an occupant of the area, the identifying comprising:
computing a first transfer function for the sound emitted from the one or more speakers at the location near the ear of an occupant of the area;
computing a second transfer function for the sound emitted from the one or more speakers at a second location in the area spatially separated from the location near the ear;
comparing the first transfer function to the second transfer function; and
identifying the second location as a candidate for the identified location at which to place a microphone if the second transfer function is matched in measure to the first transfer function;
placing the microphone at the identified location; and
generating, in response to sound detected by the microphone, a noise-canceling audio signal adapted to attenuate one or more frequencies in the sound detected by the microphone.
2. The method of claim 1 , wherein the microphone is a virtual microphone comprised of multiple microphones placed in the area.
3. The method of claim 2 , further comprising combining signals produced by the multiple microphones to produce a composite response with acoustic characteristics that are matched in measure to the acoustic characteristics of the emitted sound at the location near an ear of the occupant of the environment.
4. The method of claim 1 , wherein the acoustic characteristics include phase and magnitude of the sound emitted from the one or more speakers.
5. The method of claim 1 , further comprising determining the second transfer function is matched in measure to the first transfer function if a phase component of the second transfer function is within 35 degrees of a phase component of the first transfer function, and if a magnitude component of the second transfer function is within −8.5 dB or +4.5 dB of a magnitude component of the first transfer function.
6. The method of claim 1 , wherein the area is a passenger compartment of a vehicle.
7. A vehicle comprising:
a passenger compartment;
a noise-cancellation system comprising:
one or more speakers disposed within the passenger compartment, the one or more speakers emitting sound; and
a microphone disposed within the passenger compartment at a location where the sound emitted by the one or more speakers has a transfer function from the one or more speakers to the microphone that is matched in measure to a transfer function of the sound emitted from the one or more speakers to a location at an ear of an occupant of the passenger compartment, the microphone producing a signal in response to detecting sound; and
a controller receiving the signal produced by the microphone and, in response to the signal, generating an output signal,
wherein, in response to the output signal, the one or more speakers emit a noise-canceling audio signal adapted to attenuate one or more frequencies in the sound detected by the microphone.
8. The vehicle of claim 7 , wherein the microphone is a virtual microphone comprised of multiple microphones placed within the environment.
9. The vehicle of claim 8 , further comprising a controller receiving the signals produced by the multiple microphones, combining these signals to produce a composite signal with acoustic characteristics substantially equivalent to the acoustic characteristics of the emitted sound at the location near an ear of an occupant of the environment.
10. The vehicle of claim 7 , wherein each transfer function has a magnitude component and a phase component.
11. The vehicle of claim 7 , wherein the transfer functions are matched in measure to each other if a phase component of one of the transfer functions is within 35 degrees of a phase component of the other of the transfer functions, and if a magnitude component of one of the transfer functions is within −8.5 dB or +4.5 dB of a magnitude component of the other of the transfer functions.
12. The vehicle of claim 7 , further comprising an amplifier receiving and amplifying the output signal produced by the controller and sending the amplified output signal to the one or more speakers for emission.