Factors influencing equal-loudness-level contours

Abstract

Data on equal-loudness-level contours taken from the literature show considerable differences between the results of different laboratories, even when using the recommended alternative forced-choice (AFC) method. Some of these differences can be attributed to free parameters in the procedures that the experimentator could change. This work investigates the influence of the experimental setup on the resulting curves obtained with an adaptive two-alternative forced-choice procedure for the 30- and 50-phon curves in the range from 200 Hz to 1 kHz. For the adaptive procedure, the amount of change in the resulting equal-loudness-level contours is measured for different free parameters (e.g., initial step size, starting level). It is shown that for a simple adaptive procedure the influence of the starting level is smaller than the range effect when using the method of constant stimuli. The effect of the starting level is reduced when using large initial step size in the adaptive procedure. However, the effect can still amount to 6 dB. This effect diminishes when using an interleaved procedure. The maximum measurement error for the different procedures is estimated. In addition, it is shown that interindividual variance is reduced when the individual threshold is taken into account.