Simplified exponential horns

Abstract

The exponential horn is known as the shape realizing the best matching between a source and the external field for frequencies higher than its cut-off frequency. In practice, the horn being of finite length the effective cut-off is significantly higher and resonances appear as waves are reflected at the end of the horn. So, the response of the horn is far from being flat. Then, a question arises: in what extend the shape of an exponential horn has to be strictly respected in order to keep its main acoustical properties. The present paper intend to answer this question. First, a review of the different ways to calculate the input impedance of a horn and their accuracy is made. Comparison with input impedance measurements show that plane wave approximation is often sufficient even when the horn is strongly bended. Second, some criteria are proposed to characterize horns ability to match with the external field. These criteria are finally used to compare the performances of some simplified geometries of horn...