Loudness of sounds with a subcritical bandwidth: A challenge to current loudness models?

Level differences at equal loudness were measured for bandpass noises centered at 1.5 kHz with bandwidths from 5 to 405 Hz and a 1.5-kHz pure tone. Irrespective of the reference (tone or 135-Hz wide noise), the data indicate a decrease in loudness with increasing bandwidth. This is at odds with the assumption of stationary loudness models that loudness for sounds with a subcritical bandwidth is determined by the intensity and center frequency only. It is also not in agreement with dynamic loudness models, which predict higher levels for a tone than for equally loud noises, i.e., the opposite effect.