Abstract:

Using an IBM compatible PC, an inexpensive and simple method was developed to conduct acoustic absorption measurements in a reverberant chamber. The technique provided random noise distributed around 1/3 octave band center frequencies from 200 to 1000 Hz, through a D/A converter, to speakers within the chamber. Turbo-Pascal software was written to create a random noise file for each of the 1/3 octave bands. As a consequence, while a random noise signal was sent by the computer, that signal was identical for each experiment, for a specific 1/3 octave band. The noise signal, of 3-s duration, was programmed to increase to maximum intensity, and decrease to zero over a period of 25 (mu)s, eliminating a steplike transient to the dynamic system at termination. The decaying noise was sampled 1000 times per second using an A/D converter, and the decay rate calculated. This technique was initiated with a keystroke and produced a sound-pressure level versus time plot file, allowing determination of the reverberation time and absorption coefficient of the chamber.