Sound Radoation From a Housing Containing an Acoustic Source

Abstract

To study acoustic transmission path from the inside to the outside of rectangular enclosures, a simple gear box model made of 1.1mm, 2.3mm and 9.0mm steel plates, has been examined by means of acoustical holography. The behavior of sound radiation depends on the relation between the bending wave length in plate (λ_pl) and the sound wave length in air (λ_air). The high frequency sound (λ_pl/λ_ajr>1.5) is radiated from all over the plate according to its resonant mode. However, the sound in the lower frequency range (λ_pl/λ_air>1.5) is apparently radiated only from the edges with less power than that of the former condition. This is attributed to the radiation in the tangential directions of side plates. The result would be applicable to designing a gear system for noise attenuation.