Active muffler

In the active muffler disclosed herein, a porous flow resistive member defines a wall of a duct carrying a noisy flow, e.g., a jet exhaust. The flow resistive member is characterized by having a flow resistance substantially less than rho c, the characteristic impedance of the acoustic medium. Louds...

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Bibliographic Details
Main Author VER; ISTVAN L
Format Patent
LanguageEnglish
Published 12.12.2000
Edition7
Subjects
ACOUSTICS
ACOUSTICS NOT OTHERWISE PROVIDED FOR
BLASTING
COMBUSTION ENGINES
ENGINE PLANTS IN GENERAL
GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNALCOMBUSTION ENGINES
GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES ORENGINES IN GENERAL
HEATING
HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
JET-PROPULSION PLANTS
LIGHTING
MACHINES OR ENGINES IN GENERAL
MECHANICAL ENGINEERING
METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING,NOISE OR OTHER ACOUSTIC WAVES IN GENERAL
MUSICAL INSTRUMENTS
PHYSICS
SOUND-PRODUCING DEVICES
STEAM ENGINES
WEAPONS
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Summary:In the active muffler disclosed herein, a porous flow resistive member defines a wall of a duct carrying a noisy flow, e.g., a jet exhaust. The flow resistive member is characterized by having a flow resistance substantially less than rho c, the characteristic impedance of the acoustic medium. Loudspeakers in a chamber on the side of said porous member opposite the duct are actuated to reduce acoustic pressure in the region between the porous member and the loudspeaker, thereby increasing the acoustic flow through the porous member which in turn increases the dissipation of acoustic energy in the duct. The apparatus is particularly effective at low frequencies where a passive dissipative muffler would be of impractical size.
Bibliography:Application Number: US19970850036