Mitigating low-frequency sound with tunable acoustic chimneys.

Abstract

A way to absorb and filter low-frequency sound that is generated by sound sources in one or more enclosures is described. A sound generating room is encapsulated within an outer acoustic absorbing room that contains various openings to several acoustic ducts. The acoustic ducts function as an acoustic waveguide to the open air. At each end of the acoustic duct is an impedance matching tapered acoustic horn. In the sound generating room the horn serves as an acoustic absorber that tapers sound into the acoustic duct. At the opposite end, the horn serves as an acoustic radiator of sound energy to the open air. Both radiator and absorbers may be tuned to transmit frequencies past a certain cutoff. The effect is similar to a pressure release valve. The acoustic waveguides may be coupled to tunable passive or active noise mitigation devices such as Helmholtz resonators and low-frequency noise sources that utilize phase information.