Apparatus for measuring the absorption of sound by noise in one dimension.

Abstract

A travelling wave tube for the study of high intensity acoustics has been constructed. The tube has inner diameter two inches and length 70 feet, and consists of seven 10 foot long sections smoothly joined by collars and flanges. Attached to one end is a housing that contains two JBL horn drivers connected to the tube by a "Y" adapter. An anechoic end termination spans the length of the last section. The termination is made of steel wool of tapered density distribution. Pulse reflection measurements yielded an absorption of 40 dB or greater for frequencies of 500 Hz and higher. Reflected signals of the junctions were typically 40 dB down. Linear attenuation measurements indicated no appreciable acoustic losses at the junctions. Sum, difference and second harmonic generation measurements revealed that interactions were occurring in the medium of interest (air) and were not the result of the drivers or intermodulations of the two drivers. The performance under these preliminary tests indicates that the apparatus is suitable for nonlinear acoustics investigations.