Equal-loudness contour measurement evolved from anechoic pure tones to reflective-space noise bands

Evidence

Several more recent studies, notably the work of Robinson and Dadson (1956), used pure tones presented to listeners in an anechoic chamber; their results were the ISO standard for several years. Even then, errors were identified in the contours at low frequencies. Pollack (1952) evaluated a set of equal-loudness contours for bands of noise, but the circumstances of the listening were not well specified. Stevens (1957) moved closer to typical listening conditions by employing fractional-octave bands of steady-state sounds in reflective spaces, which he used as a basis for calculating the loudness of complex sounds (Stevens, 1961). — Toole, Floyd E, Sound reproduction- the acoustics and…, 905