초록 ▼

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. Loud

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.

대표청구항 ▼

[ What is claimed is:] [1.] Apparatus for reducing acoustic energy in a gaseous acoustic medium traversing a duct passage, said apparatus comprising:a porous resistive member having a first side defining a wall of said duct passage;a chamber on a second side of said porous resistive member opposite

[ What is claimed is:] [1.] Apparatus for reducing acoustic energy in a gaseous acoustic medium traversing a duct passage, said apparatus comprising:a porous resistive member having a first side defining a wall of said duct passage;a chamber on a second side of said porous resistive member opposite said duct passage;a partition dividing said chamber into a first volume adjacent said porous resistive member and second volume separated from said porous resistive member, said partition comprising at least one aperture;at least one acoustic driver transducer mounted in said at least one aperture in said partition;at least one sensing transducer responsive to acoustic pressure, said at least one sensing transducer located in said first volume of said chamber;a controller responsive to said sensing transducer for actuating said at least one acoustic driver transducer so as to reduce acoustic pressure variation in said first volume of said chamber and thereby increase acoustic flow from said duct passage through said porous resistive member and increase the dissipation of acoustic energy propagating in said duct passage.