초록 ▼

A lined duct is divided into two parallel branches by means of a rigid partition. The phase speed of the fundamental mode in each branch depends on the liner configuration and can differ markedly from the free-space phase speed. When the liners in the two branches are not the same, the corresponding

A lined duct is divided into two parallel branches by means of a rigid partition. The phase speed of the fundamental mode in each branch depends on the liner configuration and can differ markedly from the free-space phase speed. When the liners in the two branches are not the same, the corresponding phase speeds will be different and a relative phase lag between the waves in the two branches results. This, in turn, leads to interference between these wave components (and their reflections) both at the exit and entrance of the parallel branch pair. This interference can be exploited for the purpose of obtaining a low-frequency attenuation which is substantially larger than the attenuation of the unpartitioned duct.

대표청구항 ▼

An acoustical filter for attenuating acoustic energy in a duct comprising, in combination, a duct having at least one rigid and continuous splitter plate extending longitudinally within said duct to divide the acoustic energy in said duct into at least two branched ducts of equal length; said splitt

An acoustical filter for attenuating acoustic energy in a duct comprising, in combination, a duct having at least one rigid and continuous splitter plate extending longitudinally within said duct to divide the acoustic energy in said duct into at least two branched ducts of equal length; said splitter plate preventing substantially any acoustic energy in each branched duct from coupling to the other branched duct through said plate by reflection of acoustic energy incident upon the plate back into the branched duct from whence the incident acoustic energy originated; the branched ducts having their input ends and their output ends acoustically coupled to each other, respectively; at least one of said branched ducts containing a means to alter the phase speed of the sound wave therein to define a flow path through said one branched duct having an acoustical length different from the acoustical length of the flow path through the other of said branched ducts to produce destructive wave interference at the output ends of said branched ducts and/or constructive wave interference at the input ends of said branched ducts thereby resulting in strong reflection of acoustic energy at the input ends of said branched ducts by which effects a reduced level of acoustic energy in said duct adjoing the outputs of said branched ducts is obtained.