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Hersh Acoustical Engineering, Inc.

Alan S Hersh

Bruce E Walker

Murray S Welkowsky

Edward J Rice

Larry Heidelberg

Jin Tso

The present invention is an active-control system for attenuating noise in a duct having a fluid flow. An array of stators having a longitudinal length is positioned axially within the duct. A first array of sound sources capable of generating spinning mode sound and is positioned a distance upstream of a first plane defined by the upstream-most portion of the stators, relative to the fluid flow. The upstream distance is less than the longitudinal length of the stators. A second array of sound sources capable of generating spinning mode sound and is positioned a distance downstream of a second plane defined by the downstream-most portion of the stators, relative to the fluid flow. The downstream distance is less than the longitudinal length of the stators. A controller causes the first and second arrays of sound sources to generate sound including spinning mode sound such that it cancels a portion of the noise within the fluid flow that passes through the stators.

Active control source cancellation and active control Helmholtz resonator absorption of axial fan rotor-stator interaction noise

A hybrid mode-scattering/sound-absorbing segmented liner system and method in which an initial sound field within a duct is steered or scattered into higher-order modes in a first mode-scattering segment such that it is more readily and effectively absorbed in a second sound-absorbing segment. The mode-scattering segment is preferably a series of active control components positioned along the annulus of the duct, each of which includes a controller and a resonator into which a piezoelectric transducer generates the steering noise. The sound-absorbing segment is positioned acoustically downstream of the mode-scattering segment, and preferably comprises a honeycomb-backed passive acoustic liner. The invention is particularly adapted for use in turbofan engines, both in the inlet and exhaust.

Hybrid mode-scattering/sound-absorbing segmented liner system and method

A sound generator that has a plurality of acoustic piezoelectric transducers coupled to a single Helmholtz resonator. The resonant frequency of the Helmholtz resonator and each transducer can be intentionally chosen to be different so as to be stagger tuned so that the sound generator can create intense sound waves over a broad frequency range.

Piezoelectric sound sources

Extended frequency range Helmholtz resonators particularly useful for sound absorption over a relatively wide frequency range are disclosed. The resonators are conventional Helmholtz resonators with the addition of an active acoustic driver in the resonator cavity driven at appropriate amplitudes, frequencies and phases to provide a high degree of absorption of sound not only at the resonant frequency of the resonator, but for substantial frequency bands above and below the resonant frequency. To provide the active drive to the acoustic driver in the resonant cavity, one or more microphones are used to detect the sound to be absorbed, which signal is processed and amplified to provide a drive to the acoustic driver to best absorb the incoming sound. Various embodiments are disclosed.

Extended frequency range Helmholtz resonators

A hand-held hair dryer with a high level of sound and vibration suppression. The hair dryer includes sound absorbing material attached to the inner surface of the hair dryer housing and having a selected density to provide maximum sound absorption in a relatively thin layer of material. A motor with integral fan is mounted on the hair dryer handle by an elastomeric vibration isolator so as to be isolated from the dryer housing. The fan blade noise, in part absorbed by the sound absorbing material on the inner surface of the hair dryer housing, is further grossly suppressed by special sound absorbing structures located at the extreme inlet and outlet of the housing, such as a structure functioning as a Helmholtz resonator, with that structure itself being vibration isolated from the hair dryer housing. Preferably an aerodynamically designed heater is used downstream of the fan to minimize the vortex noise. Also, vibration isolation between the handle and the main housing assembly provides good low frequency vibration absorption, particularly with the motor being supported through the handle rather than through the main housing itself. Various embodiments and other features of the invention are also disclosed.

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Calabasas, CA, United States of America

Alan S Hersh