Technical Q - Power vs. Frequency

If a cone isn't being moved, then power isn't being drawn from capacitors. So, if you set your crossover to 80hz, and have that <80hz powered externally by a sub's internal amp, then the receiver isn't spending power to move a cone at 0-80hz.

The receiver can not spend energy if it is not creating motion.

Related: If you are sending all sub-80hz info somewhere else for amplification, then you have to try really hard to spend more than 1w per channel on amplification at the receiver level.

It does not really work like you think, but it's kind of hard to explain. Power is strictly a function of voltage and current.

The signal coming from the receivers processor section is amplified via a voltage amplified stage. The signal is then sent to the power stage which can deliver the needed current. The current needed is dependent on the voltage and impedance. The imoedance is constantly changing because the speaker and the signal interact in a way to present a constantly changing impedance. Removing some of the frequencies of the signal reduces power for reasons I won't go into ( as I'm likely to not get the science quite right.)

Just think of amp power as Potential power, like the powr avail in your engine. You usually only need a fraction of it.

"And, in a related question, say the amp is set to output full range, but the speakers connected to it only go down to 60Hz. Is the amp still putting out 100w, but it just becomes wasted because the speaker can't respond effectively to it? Or is it more a case that the full power goes to the speaker, but it is just has such a poor efficiency below that 'cutoff' frequency, that the power doesn't produce any usable sound?"

I missed this the first time around.

Spitting out a full range 20hz-20khz signal to speakers that are crap below 60 hz saves nothing in terms of power, to an extent. The cone is still moving at 20-60hz, it just isn't large enough or designed well enough to produce usable sound, or at least sound loud enough to be in line with the volume of the rest of the audio. Since motion is still being produced, energy is being spent.

Now, a smaller lighter speaker that sucks at sub-80hz is easier to move than a big, heavy speaker that is great at -80hz. So, wasting motion on say a 3" cone to move it at 40hz while producing non-usable sound doesn't cost nearly as much energy as moving a much heavier 12" cone that does a much better job at 40hz. Newton's three laws of motion and all that.

Basic physics then, for the most part ). IMO, theres no waste with standard bass mangement. You filter out the bass freqs because the sub is going to handle them. The receivers amps work a bit less hard. The front speakers may sound a bit clearer when not trying to do what they don't do well...etc