SU836653A1 - Device for suppressing noise in air duct - Google Patents

Description

(54) DEVICE FOR THE ANNOUNCEMENT OF NOISE IN THE AIR DUCT

J.;

The invention relates to the field. instrumentation and can be used in the manufacture of devices for suppressing noise in the air.

A device for suppressing noise in an air duct is known, comprising a microphone, an amplifier and a loudspeaker. The phase response of this device is adjusted according to the output of the microphone, creating anti-phase oscillations of the noise signal flj.

However, this device does not effectively suppress noise due to the instability of the oscillation phase of the noise signal.

It is also known to have a noise suppression device in air consisting of a loudspeaker connected to the output of the loudspeaker and an amplifier connected to the microphone connected to three identical electrical circuits, each of which contains an IT-J filter.

However, this device also does not provide effective noise suppression due to a change in temperature, the speed of sound.

The aim of the invention is to increase the efficiency of suppressing the noise in the duct.

The goal is achieved due to the fact that the device is equipped with serially connected second microphone and automatic gain control unit, and each of these chains are connected in series with a second filter, phase detector and adjustable phase shifter loaded on a separate input of the adder, while the first filter is connected to the second inputs of the adjustable phase shifter and the phase detector, and the output of the automatic gain control unit with the inputs of the second filters of all ble chains.

The drawing shows a structural diagram of a device for suppressing noise in an air duct.

The device contains microphones I and 2, amplifier 3j filters 4, 5 and 6, adjustable phase shifters, 8 and 9, phase detectors 10, P and 12, adder 13, additional filters 14, 15 and 16, automatic gain control unit 17, loudspeaker 18 and duct 19,

A device for reducing sound transmission over an acoustic channel operates as follows.

Microphone 1 is installed in duct 19. The audio signal is amplified by amplifier 3 and goes further to the filters 4, 5, 6. Signals from the outputs of filters 4-6 are fed to adjustable phase shifters 7, B and 9 and to the first inputs of phase detectors 10, 11 and 12. Signals from additional filters 14, 15, and 16, which are tuned to the same frequencies, filters and filters 4, 5, and 6, are fed to the second inputs of the phase detectors.

Voltages from the outputs of phase detectors 10, II and 12, proportional to the phase difference between the signals, from the outputs of filters 4, 5 and 6 and additional filters 14, 15 and 16 are fed to the controlled inputs of adjustable phase shifters 7, 8 and 9. Signals from the outputs adjustable phase shifters are fed to the adder 13 and dapee to the loudspeaker 18. An additional microphone 2 is installed next to the loudspeaker 18. The signal from microphone 2 goes to the automatic gain control unit 17 and further to the inputs of additional filters 14, 15 and 16, the signal perceived microphone 2, varies in size over large limits, and the automatic gain control unit 17 keeps it on par

I

In the case of a change in the external conditions, the phase picture of the sound is disturbed and at the outputs of the phase detectors 10, 11

and 12 is a voltage that is proportional to the phase difference of the signals perceived by microphones 1 and 2. The adjustable phase shifters will be adjusted until the phases of the input signals of the microphones are matched.

Thus, the presence of an additional microphone, an automatic gain control unit for additional filters, phase detectors and adjustable phase shifters increases the noise reduction efficiency.

Claims (1)

1. Published in Japan No. 51-46401, Cl. G 10 K 11/02, 1977. 2, Published in the UK. No. 1492963, cl. G 10 K 11/00 1978 (prototype). ,