In 1967, Richard C. Heyser, a research engineer at the Jet Propulsion Laboratory of the California Institute of Technology published a paper in the AES Journal titled “Acoustical Measurements by Time Delay Spectrometry.” It described a technique whereby loudspeakers and other electro-acoustical systems could be measured in real-world spaces—without an anechoic chamber. Unfortunately, the horsepower to perform such computations using 1960s technology was impossible, but Heyser’s TDS concept drew wide acceptance.
TEF System 12, the second-generation TDS analyzer
Later, educator Don Davis organized a seminar for 20 leading audio researchers, with California Institute of Technology offering them licenses to build and operate TDS devices created by combining off-the-shelf products with a custom Heyser-designed interface.
TDS went big time in 1983, when Crown’s Techron division unveiled the TEF System 10, the first portable TDS analyzer/acoustical measurement system. Encompassing the gamut of TDS measurements, TEF (Time-Energy-Frequency) included energy time curves and the ability to show waterfall displays of audio spectra. The 40-pound suitcase unit included 96 kilobytes of RAM and a 9-inch green-phosphor screen, and it cost $14,500. However, acoustical research would never be the same, as for the first time, complex on-site measurements of systems and spaces were possible from a commercially available unit.