Helmholtz Resonators in Open Office Acoustics

Abstract

Acoustics is the only category in which a LEED-rated office building performs worse than a conventional office building. Exposed hard surfaces and lack of partitions cause easy propagation of conversational sounds between the workstations in an open office. Research has shown that excess speech levels in the office cause disturbance to its occupants, and it can affect their work performance. Sound absorbers are relied upon to remove the excess sound energy from the office space. But, to address the absorption of speech sounds, porous absorbers are not efficient. Resonant absorbers, particularly Helmholtz Resonators, are effective at low-frequency sounds and are applied to tackle the frequencies important for speech intelligibility in open offices. This research discusses the basics of Helmholtz resonators and their working principles. The classical lumped approach is used for evaluating the absorption performance of a resonator. Modifications to the basic geometry of a resonator, as explored by Selamet, S.K.Tang, Y.H.Kim, and a few others, are discussed along with their analytical formulations. Models, as given by Van der Aa and Y.H.Kim to predict the performance behavior of an array of resonators are presented, since such a system of resonators can overcome the narrow performance quality of a single resonator. Differential evolution is implemented for designing the array. The application of this array or panel in an open office improves its acoustic quality. Open office acoustic parameters like Distraction distance, Spatial decay rate, Sound Pressure Level at 4m, and the background noise level are used for evaluating the acoustic comfort. Pareto front optimization is applied to analyze the trade-offs for an optimal acoustic environment.