It's been asserted, basically as a truism, that demands on the amp go up as the frequency goes down. \n\nThis has been cited repeatedly as a reason to add a subwoofer to a given speaker setup (moving the most demanding loads to a dedicated amp). \n\nBut I can't seem to figure out where I can find that value. \n\nSpeaker sensativity is frequency independent (that is to say: the crossovers level it). So on, say, a 90db@1w speaker, the tweeter might be intrinsically more sensitive than the woofer; the crossover makes both 90db sensitive. \n\nSo [for a non-builder] where does this "extra demand" play out? 110db@40hz will require 100w, as will 110db@20khz. The only exception will be after roll-off starts; but doing custom EQ to compensate for that is really beyond the scope on my question. \n\nTo rephrase: does it really require any more power from the amp to generate Xdb at the bottom end of a speaker's flat-response than at the top? If so: what is the math? How is that draw expressed?