GB2091064A - Noise reduction - Google Patents

Abstract

A microphone - amplifier - speaker combination is used to derive anti-phase sound to destructively interfere with noise. When noise is generated outside a building most of the noise sound energy is transmitted through the window areas, and a means of converting the windows themselves into electrostatic speakers is described. These speakers are arranged to transmit the noise sound energy in anti-phase so as to nullify it. Apparatus of a portable type capable of suppressing unwanted noise generated inside a building, by anti-phase re-transmission is also described.

Description

SPECIFICATION Suppression of unwanted noise by reversed phase energy injection Noise emitted by vehicles and aircraft can be an unacceptable source of disturbance to the inhabitants of residences close to main roads and/or airports. A means of alleviating or eliminating such disturbance is described below.

It is known that sound waves are longitudinal waves consisting of alternate compressions and decompressions in the transmitting medium. If sound waves of similar energy level and frequency are propagated in the same medium and in the same direction of travel but in complete anti-phase, then the original unwanted sound will be nullified and silence will be experienced.

One form of device for producing this silence effect consists of a directional microphone having its activated side facing towards the incoming noise wave front, said microphone activating an amplifier which, in turn, activates a loud speaker arranged to project its sound output in the same direction as the incoming noise wave front but so connected that a compression portion of the noise sound wave is projected by the speaker as a decompression and viceversa. The microphone must be shrouded and the incoming wave side of the speaker lagged with sound absorbing material to prevent feed back between microphone and speaker. The microphone must be sited preferably in the same plane as the activated member or diaphragm of the speaker but not more than 30 centimeters from this member on the incoming noise wave side.It should be adjusted so that its directional reception is substantially normal to the incoming noise wave front.

Experiments have shown that in well constructed buildings nearly all disturbing exterior noise is transmitted into the building through the window areas. Exterior noise silencing effect can, therefore, be most efficiently exploited if the windows themselves are constructed as electrostatic loudspeakers, by treating the indoor side of the existing glass with a transparent conducting material and fitting a flexible pane of transparent plastic, similarly treated on its outdoor facing surface, on the indoor side of the existing treated window. This flexible member will then act as the diaphragm of the speaker. When this device is adopted it is essential that the micorphone be mounted outside the window and be lagged with sound absorbing material on its non activated side.

For large window areas more than one microphone may be necessary.

The device will normally be produced as a portable unit, mounted on an adjustalbe stand and embodying the microphone, speaker and amplifier.

This unit can then be sited in front of the window area of a room which is inhabited at the time. This portable arrangement can also be used when objectionable noise is generated inside a building and transmitted through partition walls, doors or ceilings, or directly generated in a crowded area, such as an open plan office or a hospital ward. The stand on which the microphone - cum - speaker and amplifier is mounted should be capable of generaous adjustment for height and direction to arrive at optimum performance.

In order to avoid interference zones, this portable type of unit should be fitted with either a loud speaker of the electrostatic type, having a diaphragm of iarge area, or a plurality of conventional speakers, each shrouded so that the sound waves emitted by one does not cause interference zones between itself and another adjacent speaker.

When the device is operating it is, of course, necessary to adjust the volume of the speakers sound output to match the volume of the received disturbing noise.

1. A means of eliminating or alleviating unwanted noise which is generated inside or outside a building by the reception and re-transmission of the noise wave system in absolute anti-phase and with sound energy substantially equal to the offending noise sound waves, the transmission of the anti-phase sound being in the same direction of travel as the received noise wave and said transmission being accomplished by the use of a microphone, amplifier and speaker combination, either fixed or portable as described.

2. A means of noise suppression inside a building when the offending noise is generated outside the building by the use of apparatus as described in Claim 1, but, by suitable adaption, causing the windows of the builidng to act as an electrostatic speaker or speakers.

3. A portable noise suppression unit as described in Claim 1 having generous means of adjustment of the microphone - cum - speaker unit, so that it can be used inside a building to alleviate or eliminate unwanted noise generated in the building and transmitted either direct or through walls, doors, floors or ceilings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Suppression of unwanted noise by reversed phase energy injection Noise emitted by vehicles and aircraft can be an unacceptable source of disturbance to the inhabitants of residences close to main roads and/or airports. A means of alleviating or eliminating such disturbance is described below. It is known that sound waves are longitudinal waves consisting of alternate compressions and decompressions in the transmitting medium. If sound waves of similar energy level and frequency are propagated in the same medium and in the same direction of travel but in complete anti-phase, then the original unwanted sound will be nullified and silence will be experienced. One form of device for producing this silence effect consists of a directional microphone having its activated side facing towards the incoming noise wave front, said microphone activating an amplifier which, in turn, activates a loud speaker arranged to project its sound output in the same direction as the incoming noise wave front but so connected that a compression portion of the noise sound wave is projected by the speaker as a decompression and viceversa. The microphone must be shrouded and the incoming wave side of the speaker lagged with sound absorbing material to prevent feed back between microphone and speaker. The microphone must be sited preferably in the same plane as the activated member or diaphragm of the speaker but not more than 30 centimeters from this member on the incoming noise wave side.It should be adjusted so that its directional reception is substantially normal to the incoming noise wave front. Experiments have shown that in well constructed buildings nearly all disturbing exterior noise is transmitted into the building through the window areas. Exterior noise silencing effect can, therefore, be most efficiently exploited if the windows themselves are constructed as electrostatic loudspeakers, by treating the indoor side of the existing glass with a transparent conducting material and fitting a flexible pane of transparent plastic, similarly treated on its outdoor facing surface, on the indoor side of the existing treated window. This flexible member will then act as the diaphragm of the speaker. When this device is adopted it is essential that the micorphone be mounted outside the window and be lagged with sound absorbing material on its non activated side. For large window areas more than one microphone may be necessary. The device will normally be produced as a portable unit, mounted on an adjustalbe stand and embodying the microphone, speaker and amplifier. This unit can then be sited in front of the window area of a room which is inhabited at the time. This portable arrangement can also be used when objectionable noise is generated inside a building and transmitted through partition walls, doors or ceilings, or directly generated in a crowded area, such as an open plan office or a hospital ward. The stand on which the microphone - cum - speaker and amplifier is mounted should be capable of generaous adjustment for height and direction to arrive at optimum performance. In order to avoid interference zones, this portable type of unit should be fitted with either a loud speaker of the electrostatic type, having a diaphragm of iarge area, or a plurality of conventional speakers, each shrouded so that the sound waves emitted by one does not cause interference zones between itself and another adjacent speaker. When the device is operating it is, of course, necessary to adjust the volume of the speakers sound output to match the volume of the received disturbing noise. CLAIMS

1. A means of eliminating or alleviating unwanted noise which is generated inside or outside a building by the reception and re-transmission of the noise wave system in absolute anti-phase and with sound energy substantially equal to the offending noise sound waves, the transmission of the anti-phase sound being in the same direction of travel as the received noise wave and said transmission being accomplished by the use of a microphone, amplifier and speaker combination, either fixed or portable as described.

2. A means of noise suppression inside a building when the offending noise is generated outside the building by the use of apparatus as described in Claim 1, but, by suitable adaption, causing the windows of the builidng to act as an electrostatic speaker or speakers.

3. A portable noise suppression unit as described in Claim 1 having generous means of adjustment of the microphone - cum - speaker unit, so that it can be used inside a building to alleviate or eliminate unwanted noise generated in the building and transmitted either direct or through walls, doors, floors or ceilings.