Noise loudness is level-independent until bandwidth exceeds the critical bandwidth.

Evidence

The data show that band-pass noise of small bandwidths is as loud as the I-kHz tone of the same level. This simple relationship holds only up to a certain bandwidth. This bandwidth at 1 klh is about 160 Hz, and corresponds to the critical bandwidth. For bandwidths above the critical bandwidth, the loudness of the band-pass noise increases, i.e. the level of the equally loud I-kHz tone given as the ordinate increases. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1203

Categorization

• QUESTION: How exactly does loudness integrate across critical bands above the critical bandwidth — is it a sum-of-parts model? This is likely developed in the next chapter on loudness summation.