Low frequency sound attenuation in a flow duct using a thin slow sound material

TL;DR

This paper introduces a thin, subwavelength slow sound material for duct attenuation that effectively reduces low-frequency noise in airflow channels by slowing sound with folded side branch tubes, showing promising broadband performance.

Contribution

The study presents a novel thin slow sound material with folded side branches that achieves wide-band low-frequency attenuation in airflow ducts, with detailed impedance analysis and flow effects.

Findings

Large broadband attenuation at low frequencies in air ducts.

Flow increases interface losses, enhancing attenuation.

Impedance tuning is crucial for optimal performance.

Abstract

We present a thin subwavelength material that can be flush mounted to a duct and which gives a large wide band attenuation at remarkably low frequencies in air flow channels. To decrease the material thickness, the sound is slowed in the material using folded side branch tubes. The impedance of the material is compared to the optimal value, which differs greatly from the characteristic impedance. In particular, the viscous and thermal effects have to be very small to have high transmission losses. Grazing flow on this material increases the losses at the interface between the flow and the material.