Attenuation of sound waves in ducts

Details Attenuation of sound waves in ducts Attenuation of sound waves in ducts

1977-09-07

1978-08-22

Brown, Thomas W.

Acoustics

Anatomic or prosthetic relation

Ear and mouth

181206, E04B 199, G10K 1104

Patent

active

041091086

ABSTRACT:
Apparatus for attenuating a sound wave propagating in a given direction along a fluid-containing duct comprises two sound sources spaced along the duct in a given direction; a sound detector between the two sources at a null point at which sound emanating only from the two sources substantially cancels; and means for utilizing the output of the sound detector including a phase-shifter and a frequency-sensitive amplifier to control the operation of the sound sources so that they emit sound in relative antiphase and at equal amplitudes and at such phases relative to the phase of the detected sound that the resultant of the sound radiations emitted in the given direction substantially attenuates the sound wave propagating along the duct.

REFERENCES:
patent: 2043416 (1936-06-01), Lueg
patent: 4044203 (1977-08-01), Swinbanks
M. Swinbanks, "Active Control of Sound Propagation in Long Ducts", J. of Sound and Vib. (1973), 27(3), pp. 411-436.
M. Jessel and G. Mangiante, "Active Sound Absorbers in an Air Duct", J. of Sound and Vib. (1972), 23(3), 383-390.

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