Conical Apertures in Panels; Sound Transmission and Enhanced Absorption in Resonator Systems

The sound transmission loss and the input impedance of conical apertures in walls are calculated extending the classical work of Wilson and Soroka [1] on cylindrical apertures and the work of Mechel [2] on slit shaped apertures. The input impedance is used to design distributed Helmholtz resonator type of absorbents; a perforated panel placed at a given distance in front of a hard wall or ceiling. Calculations, corroborated by measurements both in a standing wave tube and in a reverberation room, show that using conical shaped apertures as opposed to normal holes or slits may greatly enhance the capability of absorbers of thick panels as gypsum, wooden chipboard, plywood etc.