The extension of digital acoustics measuring techniques to higher frequencies

Abstract

The majority of acoustic measurement criteria are derived from the integral of the squared sound pressure. This work shows the development of an instrument capable of measuring any of the Integral Square (IS) criteria l.n acoustic scale models of rooms using an impulse sound source. The variety of measurements is made possible through the use of a computer-based instrument. The microphone signal is filtered and then digitised. All further signal processing is done digitally in the computer. The results are either displayed numerically or plotted directly on an X-Y plotter. The instrument uses logarithmic quantisation of the signal and an algorithm developed by Hanrahan (103-105) which greatly simplifies the IS calculations to a process of table look-up and summation. The decay curves are calculated using Schroeders Method (27). This study shows the design and testing of the logarithmic converter having 54dB dynamic range and 3dB quantising intervals and interfaced to a NOVA 1200 minicomputer. The software to calculate RT, EDT and IRT was developed and tested on a 1/8th scale model of a reverberation room with known characteristics.