A periodic electroacoustic waveguide for passive sound absorption

Abstract

© 2020 Proceedings of ISMA 2020 - International Conference on Noise and Vibration Engineering and USD 2020 - International Conference on Uncertainty in Structural Dynamics. All rights reserved.Electrodynamic loudspeakers can be used to absorb sound energy in a narrow frequency band around the loudspeaker resonance. To increase the operational bandwidth, active and passive impedance control techniques have been described in the literature. In this work, we propose a passive technique that makes use of a periodic array of small loudspeakers mounted as side branches along a straight duct. A larger loudspeaker is mounted at one end of the duct, which acts as a conventional narrow-band absorber. This system aims at absorbing the sound energy flowing inside the duct, leading to a small reflection coefficient at the entry of the periodic waveguide. We investigate the sound absorption of such a device through numerical simulations based on the transfer matrix method. The unit cell is made up of a one-dimensional acoustic waveguide with a side-branch loudspeaker. It is shown that the proposed approach might increase the absorption bandwidth, even with 1-inch loudspeakers and a number of cells as small as five in the periodic structure.