Individuals who subject themselves to excessively loud levels almost immediately begin to suffer an effect known as listening fatigue, wherein the ear’s sensitivity to the onslaught decreases and the listener tries to compensate by continually increasing the volume. After the volume pot reaches a certain rotation, they begin to hear excessive clipping and breakup as the amp tries to keep up with their loudness demands and runs out of power leading the listener to conclude they need a bigger amp.
IME this typically happens for one of four reasons: the speakers are non-linear in response, the amp is too low in power to really control the woofers, the speakers are poorly placed in the room creating significant bass nulls, and/or they have poor distortion performance to begin with. The bass null problem is especially common.

