Loudness of subcritical sounds as a function of bandwidth, center frequency, and level

Level differences at equal loudness between band-pass noise and pure tones with a frequency equal to the center frequency of the noise were measured in normal-hearing listeners using a loudness matching procedure. The center frequencies were 750, 1500, and 3000 Hz and noise bandwidths from 5 to 1620 Hz were used. The level of the reference pure tone was 30, 50, or 70 dB. For all center frequencies and reference levels, the level at equal loudness was close to 0 dB for the narrowest bandwidth, increased with bandwidth for bandwidths smaller than the critical bandwidth, and decreased for bandwidths larger than the critical bandwidth. For bandwidths considerably larger than the critical bandwidth, the level difference was negative. The maximum positive level difference was measured for a bandwidth close to the critical bandwidth. This maximum level difference decreased with increasing reference level. A similar effect was found when the level differences were derived from data of an additional categorical loudness scaling experiment. The results indicate that the decrease of loudness at equal level with increasing subcritical bandwidth is a common property of the auditory system which is not taken into account in current loudness models.