Active sound control on boundary layers

Abstract

Active control of sound reflection on a boundary of acoustic medium is studied based on the electro-acoustic multilayer model and the feedback control. The acoustic medium boundary is made of multiple layers of elastic materials and two electro-acoustic transducer layers that can transform acoustic signal to electric signal and vice versa. When acoustic waves are incident on the boundary, the external control circuit receives the electric signal from the transducer that measures acoustic pressure level on the boundary surface, properly filters the signal band and actuates the other transducer so that actuated acoustic waves can suppress the reflection waves. Advantage of this active approach is in the small thickness of the boundary layer configuration over passive absorption layers and in wider frequency band control over other control algorithms. This paper discusses the controllability of the active boundary layers from the view of time delay caused from the thickness of transducers layers, and its affect on the reflection control performance and stability.

Development of Multilayer Transducer and Omnidirectional Reflection Model for Active Reflection Control

“…The transducer of the above structure was fabricated, and the performance test was conducted using a pulse tube. When it was uncontrolled, it showed a decrease of 2–3 dB, and when it was controlled, the sound absorption performance was around 20 dB [ 15 ]. Among the studies of analytic active sound absorbers, 1–3 composites were used.…”