Headphone calibration shifted from subjective listeners to probe mics and HATS

Evidence

In the early 1980s a similar subjective loudness procedure as described above was employed but alternative methods were also explored. In one method, a probe microphone was placed in the ear canals of the listener to measure and then match the transfer function of the headphone to that of the sound field (Theile, 1986). A more repeatable and safer approach was to substitute the listener with a head and torso simulator (HATS). A third option was to use a headphone known to be DF calibrated and compare its performance with the headphone under test. — Toole, Floyd E, Sound reproduction- the acoustics and…, 1766