Hybrid membrane resonators for multiple frequency asymmetric absorption and reflection in large waveguide

TL;DR

This paper introduces hybrid membrane resonators (HMRs) that function as Helmholtz resonators for asymmetric sound absorption and reflection in waveguides, demonstrating high efficiency at multiple frequencies with potential for duct noise reduction.

Contribution

It presents a novel design of hybrid membrane resonators capable of multi-frequency asymmetric absorption and reflection, outperforming traditional Helmholtz resonators in size and frequency coverage.

Findings

Achieved over 97% absorption at 286.7 Hz with two single-frequency HMRs.

Observed 60-80% absorption at multiple frequencies with multiple-frequency HMRs.

Experimental results closely match theoretical predictions.

Abstract

We report that Hybrid membrane resonators (HMRs) made of a decorated membrane resonator backed by a shallow cavity can function as Helmholtz resonators (HRs) when mounted on the sidewall of a clear waveguide for air ventilation. When two single-frequency HMRs are used in the same scheme as two frequency-detuned HRs, asymmetric total absorption/reflection is demonstrated at 286.7 Hz with absorption coefficient over 97 % in a waveguide 9 cm x 9 cm in cross section. When two multiple-frequency HMRs are used, absorption in the range of near 60 % to above 80 % is observed at 403 Hz, 450 Hz, 688 Hz, 863 Hz and 945 Hz. Theoretical predictions agree well with the experimental data. The HMRs may replace HRs in duct noise reduction applications in that at a single operation frequency they have stronger strength to cover a much larger cross section area than that of HRs with similar cavity volume, and they can be designed to provide multiple frequency absorption band.