Experiments on sound-absorbing Shaw-type horns with spatially varying effective density

Abstract

An experimental investigation of Shaw’s theory of sound propagation in acoustic horns with spatially varying density and elasticity is reported. The density-variation technique was used to simulate a conical horn in a tube of uniform cross section using perforated sheet metal plates. The performances of the density variation horn and the equivalent conical horn were evaluated by comparison of the acoustic impedance and the acoustic pressure within the horns. It was observed that the density-variation conical horn had sound-absorbing properties as a result of the use of the perforated plates. Due to the absorption properties of the density-variation cone it can be used as a muffler. A muffler was designed and its performance evaluated using both a loudspeaker and an internal combustion engine as sound sources.