Browse Prior Art Database

Audible Noise Suppression

IP.com Disclosure Number: IPCOM000034221D
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 3 page(s) / 29K

Publishing Venue

IBM

Related People

Pattnaik, P: AUTHOR [+3]

Abstract

A technique is described whereby the audible noise produced from noisy devices, such as fans and disk drives as used in personal computers, is suppressed. The concept incorporates out-of-phase waveform technology for the cancellation of the audible noise. Generally, audible noise produced from noisy devices, such as fans and disk drives, is present at a relatively constant low frequency for a defined period of time. As a result, the periodicity of the dominant component of the noise can be used to produce an out-of-phase signal so as to cancel out most of the noise. The concept described herein incorporates a self-calibrating assembly of electrical components so as to produce the cancelling out signal.

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Audible Noise Suppression

A technique is described whereby the audible noise produced from noisy devices, such as fans and disk drives as used in personal computers, is suppressed. The concept incorporates out-of-phase waveform technology for the cancellation of the audible noise. Generally, audible noise produced from noisy devices, such as fans and disk drives, is present at a relatively constant low frequency for a defined period of time. As a result, the periodicity of the dominant component of the noise can be used to produce an out-of-phase signal so as to cancel out most of the noise. The concept described herein incorporates a self-calibrating assembly of electrical components so as to produce the cancelling out signal. The assembly, as shown in the figure, consists of signal generator 10, two microphones 11 and 12, controller 13, delay unit 14 and speaker 15. Signal generator 10 generates a waveform whose amplitude and frequency is controlled by the voltage levels at the input pins from controller
13. Condenser type microphones 11 and 12 are positioned so that microphone 11 is close to the noisy device to collect samples of the noise generated. Microphone 12 is positioned either outside of the personal computer or far from the noise and speaker. It functions as the feedback of information for controller
13. The feedback information is used to control the amount of delay generated by delay unit 14 which introduces a delay of from zero to fifty milliseconds through the line from controller 13. Controller 13 interfaces to microphones 11 and 12 through low-pass filters which remove signals above 70 Hz. As a result, the signals seen by the rest of the controller are only the dominant components of the noise. The RMS value of the input signal from microphone 11 is used for the input to the first input pin of signal generator 10 and the frequency of the signal from this microphone is used to control the second input pin of signal generator 10. The signal from microphone 12, after passing through the low- pass filter, is used for controlling delay unit 14 by means of a feedback loop so as to minimize the signal. The noise suppression functions when microphone 11, near the noisy device, picks up the noise signal. After amplifying the signal, it is broadcast back through noise cancelling speaker 15 in reverse phase. Typically, noise-cancelling speaker 15 is positioned above the device which is producing the noise, generally above the loudest component in the enclosure. The intent is to cancel out this sound so that a large percentage of it never leaves the unit. The intensity and frequency of the air movement caused by a fan, or other periodic sound producers, is reduced to a minimum by introducing the speaker sound waves, which oscillate in exact opposition to the audible sound waves, so as to cancel out the magnitude of the oscillations. Since most personal computers are equipped with a small speaker, this speaker could be used f...