The sound field at the mouth of a horn

Abstract

The nature of the sound fields at the mouths of two small axisymmetric horns was investigated experimentally. An automated traverse system was used to measure the pressure across the mouth of each horn, and the results were decomposed into amplitudes and phases of cylindrical mode solutions to the Helmholtz equation. The circumferential variation of the sound fields was examined, and the existence of plane waves above a certain limiting frequency was tested. The results of measurements at the horn mouths were then compared with numerical models of the horns using two alternative boundary element based techniques, a traditional direct Boundary Element Method (BEM) and a new source superposition technique. The source superposition method is more efficient than direct BEM, but provides only approximate solutions in the near field. The accuracy of the near field pressure solution was investigated and conclusions drawn as to the utility of the source superposition technique in modelling horn loaded loudspeakers.