Newton,
The decline in LF hearing sensitivity as level is reduced is usually portrayed by a set of hearing sensitivity curves published by Fletcher and Munson, of Bell Labs IIRC. Preamps and receivers with a knob or switch labeled "loudness" usually try to implement an inverse of these (or newer) curves. I suppose it's conceivable that the distortion of a tube amp could to some extent give a greater sense of fullness to which Rhljazz alludes, but I wouldn't imagine that would match the loss in sensitivity as level is reduced.
db
The decline in LF hearing sensitivity as level is reduced is usually portrayed by a set of hearing sensitivity curves published by Fletcher and Munson, of Bell Labs IIRC. Preamps and receivers with a knob or switch labeled "loudness" usually try to implement an inverse of these (or newer) curves. I suppose it's conceivable that the distortion of a tube amp could to some extent give a greater sense of fullness to which Rhljazz alludes, but I wouldn't imagine that would match the loss in sensitivity as level is reduced.
db