A microcomputer-controlled system for laboratory reverberation measurements

In the Lord Corporation 423 cubic meter reverberation room, a microcomputer-controlled instrumentation system has been implemented to measure sound absorption and to determine sound power. The kernel of the system is a Cromemco Z-2D microcomputer (Z-80 microprocessor) with dual disk drives and a seven-channel A/D converter. Amplified and filtered microphone signals are taken directly from the parallel outputs of a General Radio 1/3-octave multifilter and fed to an in-house built interface. The interface consists of 28 parallel true rms detectors (Analog Devices ♯536) and seven 4X-multiplexers (RCA ♯CD4151). An important feature of the AD536 converter is the availability of a decibel output with a useful dynamic range of 60 dB. Separate averaging time constants can be selected for each channel. The overall system is quite inexpensive yet extremely flexible and powerful; both Fortran IV and 16K Extended Basic software are available. A description of the system and its performance are given.