Left/ right: Daniel Casado (PNW committee), Mark DeArman (Cascade Acoustic Research), and Steve Malott (PNW chair) at March 2015 PNW meeting on audio measurements.
The March PNW Section March meeting welcomed Mark DeArman of Cascade Acoustic Research (Puyallup, WA) who spoke about audio band test and measurement systems, with an acoustic focus. A broad overview of essential types and configurations of such systems, as well as theory of operation and software analysis was given. Mark formed the business to address the needs of regional pro audio speaker manufacturing. 27 AES members were among the 41 total attendees.
As a broad overview of what's around for acoustic test and measurement, Mark described three general categories - single channel devices (like a sound level meter or RTA); dual channel systems (synched analysis channels allow any test signal); and single/multichannel with coherent clocking. Some details of operation and advantages/disadvantages of each were given.
Next, Mark spoke of measurement methods in more detail, including reviews of sampling theory, Fourier analysis, and filtering. One port devices included the sound level meter, oscilloscope, spectrum analyzer/RTA (Real Time Analyzer). Some time was spent reviewing windowing for data acquisition.
Two-port tests were then described, which use an input, device under test (DUT) and output to obtain a transfer function. After a review of mathematical modeling, Mark spoke about the direct form used by many test systems such as dual channel FFT and MLS, and matched filtering, including Richard Heyser's Time Domain Spectrometry (TDS).
Finally, some relationships to speaker testing were given, and there was a demo of a compression driver testing apparatus Mark developed, suitable for production line testing for problems like rub/buzz and distortion.
