Helmholtz Resonators Revisited

Tremendous efforts are extended by ambitious acousticians to invent new means for attenuating airborne sound in one way or another, be it for noise control or room acoustic purposes. Relatively few of these, however, prove successful in technical realizations. Ever so often, in an attempt to make them fit practical requirements under real working conditions, they turn out to become awfully intricate and hence indisputably expensive. Stimulated by three recent publications in this journal, which all dealt with rather complicated reactive structures derived from the ancient Helmholtz resonator principle, two relatively simple sound attenuators (so-called membrane and micro perforated absorbers) are briefly recalled here which could be qualified for solving several specific noise control and room acoustic problems of practical relevance. These are two representative examples of a larger family of sound absorbing devices investigated by the Fraunhofer Institute in the past and developed for future applications in which fibrous or porous damping materials are unwanted or dispensable.