Actually, our ears have 3 different mechanisms for dealing with how loud the ambient sound level is and adjusting to them. One is nerves inhibiting neighbors, which helps bring signal above noise regardless of the sound level. Another is the set of muscles that tighten our eardrums during loud noises (ever notice how your often hear and feel a scrunching thing going on in your ears when the loud noise stops, or the damn guitarist turns down? That’s the muscles relaxing.) There’s a third which I can’t remember at present but is probably covered nicely in wikipedia.
Our ears can handle an amazing 100 decibels or more in range from the quietest to the loudest sounds. That’s 10 orders of magnitude, in terms of sound pressure! (Square that, to get it in terms of energy levels.) It’s astonishing.
So, you want yet another adaptation to handle an even wider range? For what? What evolutionary environment would require an even higher range? 100dB SPL (what they used to call the “pain threshold” but what we now call a “not terribly loud band”, reserving that for 110 dB SPL) is really quite loud. Unless we’re all living underneath 747’s constantly taking off, it’s really quite enough.