Effects of attenuation, dispersion, and high sound-pressure levels on acoustic wave distortion in horns

Abstract

High-power sound sources have received a lot of attention in the past few years due to renewed interest in industrial applications of high-intensity sounds such as the acoustic agglomeration of aerosols or combustion enhancement. Most high-power sound sources require a horn to match the source impedance to the medium where the sound is radiated. Such horns introduce distortion in the initial waveform, which can be detrimental to the agglomeration or combustion enhancement process. Boundary-layer attenuation smooths the wave shape while dispersion breaks up the symmetry of the waveform. Horn-induced dispersion is usually the dominant dispersion mechanism, resulting in strong peaks in the waveform. Finally, due to the very high acoustic levels at the horn throat, finite-amplitude effects are responsible for a significant amount of distortion at high frequencies. Simple examples of waveform distortion due to these various mechanisms are shown. The effects of sound-pressure level, horn design, and frequency on distortion are illustrated for an exponential horn and several initial wave shapes. Experimental results are presented that compare very well with theory.