BEM computations of a finite-length acoustic horn ann comparison with experiment

摘要

Classical horn theory calculates the throat impedance to predict the performance of a finite length horn by using the exit boundary condition that the impedance there is that of a rigid pistion in an infinite baffie. Historically such calculations have not seemed to produce good correlation between the radiated pressure response in the far-field and the caluclated throat impedance. In this re-examination of horn theory, the throat impedance is calculated for a finite three-dimensional exponentially-flared horn by the Boundary Element Method representing the horn boundaries by planar elements. Teh calculated impedance, for the wtihout and with finite-baffle cases, is compared with the classical theory and computed far-field response. The computed results are also compared with the classical theory and computed far-filed response. The computed results are also compared with a novel measurement technique for measuring the throat acoustic impedance using a fiber-optic probe for determining the loudspeaker driver motion. It is shown that there is excellent correlation between the frequency peaks in the far-field pressure and the throat impedance both for the BEM calculations and for the experimental measurements.