Sensory pleasantness stays flat up to 20 sone then declines with loudness

Evidence

Sensory pleasantness, however, depends also on loudness in such a way that up to about 20 sone, there is little influence. For values larger than 20 sone, sensory pleasantness decreases. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1372