You can prove that it's not about long wavelengths if you think about set of good headphones or earphones. They have no problem producing fundamental tones way down to the limit of hearing, and yet there is virtually no room for the long wavelengths to propagate.I moved from talking about amps to talking about basses there, maybe it was unclear. How come it's not about long wavelengths?
Where long wavelengths do become a factor is when you go about eq'ing a room and you have deal with nodes, modes, and standing waves.