That explains a lot, Chojin, in terms that the average person can understand. I had no idea that the response of the ear to the frequencies of sound, and the SPL too I suppose, has such an affect on the sound we perceive; as opposed, I guess to the actual sound wave pattern generated by the amp and speaker and pushed thru the air. It sounds like what we hear is regulated by our human condition; and this seems to me to suggest why dogs, for instance, can hear things we cannot hear and can also hear things way "before" we hear them. The condition of being a dog bears with it an ability to perceive sound, as it moves thru the air, differently from us because their ears respond to sound differently from our ears do. Is this why dogs will often howl in response to a fire siren, while we respond to it passively?

Our sensory perception as humans, in this case the perception of sound waves, is seemingly limitted to only part of the full spectrum of sound wave frequencies and wavelengths in nature or the physical world. I am aware somewhat of that, just like our eyes perceive only a fraction of the electromagnetic spectrum - visible light. But the graphic representation of what our ears actually perceive as the volume of sound waves must form a curve on an x/y graph where the steadily increasing volume of a frequency is a straight line on the graph. And furthermore, from your description, the curve on the graph representing the volume our ears perceive must be a differently shaped curve for all frequencies as the volume of that frequency is increased.

Or something like this if represented in a graph where the volume of a frequency increases linearly on a graph and is represented on the graph as a straight line.

This phenomenon must have been a great mystery to early sound engineers or the predecesors of sound engineers, and must have been difficult to explain until the science of human hearing had been developed. Experts in the arts and science of sound must have been aware of this phenomonon long before it could be definitively explained and their theories validated.

A lot of us are still unaware of these principles, but dudes playing in bands, especially loud bands, figured out quite unscientifically that more powerful amps produced bass sounds more satisfying to the ear.

Is this similar, in a sense, to why deep bass woodwind instruments tend to be huge; such as in huge bass or baritone saxiphones? And in the case of drums, the need for a large bass drum instead of just tuning down a smaller tom for instance?

Why someone would need a 100 watt amp has turned out to have a lot more to it than I would have casually thought. Excellent thread.