Optimisation of a controllable Helmholtz resonator to achieve high frequency reconfigurability with large absorption values

Abstract

Helmholtz resonators (HR) are effective acoustic absorbers in the low frequency regime, where the performance of conventional porous absorbers is limited. This is evident by their widespread applications, from controlling room modes to reducing noise transmission in ducts and fan noise radiated by aero-engines. However, HR-based sound absorbers only achieve significant sound absorption within a narrow frequency range. Thus, HR can become ineffective as soon as the acoustic environment changes (e.g., when increasing the occupancy of a room) and the problematic frequency falls outside the HR’s target frequency range. In response to the dynamically changing acoustic environment, a controllable HR with a large frequency reconfigurability range would be required. Recent research efforts have focused on reconfigurable HR that enable resonance frequency tuning over a large frequency range, but the sound absorption levels of the HR were not considered. In this contribution, a numerical optimisation study of a controllable HR to achieve a high frequency reconfigurability with simultaneously large sound absorption values throughout the reconfiguration range is presented. To achieve reconfigurability, a cylindrical HR with a controllable neck radius is considered and its geometry as well as added layers of porous material in the HR cavity are optimised.

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ORCID for Felix Langfeldt: orcid.org/0000-0003-2380-2746

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