Speaker relative efficiency/sensitivity when using a high pass filter

Most of the power in music is in the low frequencies. The speaker's "power requirements" don't change. How much power you need to drive the higher frequencies depends on where you cross-over. I'd guess that amps handling 100 Hz & up can be a quarter or half the power of whatever the speaker's "requirements" are. The speaker manufacturer's upper limit should be regarded as a safety spec. Exceeding that power could damage the speaker. There is no lower limit. You don''t lose sleep because you music system is turned off, do you? Happy listening.

@erik_squires --

"Truthfully, 100W is overkill for most speakers and your average or modest listening room." 

100W (depending on their specific iteration as an amp) may be deemed sufficient to quite a few, but as a blanket statement and going so far to call it "overkill" certainly holds no truth - not least with low to moderately efficient speakers as they're, by far, most commonly found.

To those for whom 80-85dB's max. at the listening position in a no more than moderately sized and -damped room is all they are ever going to need, and they may be plentiful, 100 quality watts or even less will do just fine. Setting the bar a little higher however with recorded material less compressed (typically classical music) and getting those peaks up to, say, 105dB's as something emulating a live event at the LP - reproduced cleanly, effortlessly and with impact, that is - 100W of most any kind with lower eff. speakers will come up short. 

A varying factor also for how those 100W will actually show themselves is the specific amp and its overall quality and PSU. I've heard below 50W Class-A amps handle difficult-to-drive speakers far better and sounding more powerful than with several hundred watts Class A/B or D variants.

Make the same speaker a far less difficult load by removing its (likely complex) passive filter and turn it into an active version, and the stated wattage of most any amp will sound fairly close to its specified nature. That's likely a scenario outside the reach and intention of this thread, but nonetheless it goes to show. 

If the approximation of clean sounding, live dynamics of acoustic or amplified events are a desired goal (and why shouldn't they be if a broader measure of Fidelity is regarded as important in this field of ours?), then 'overkill' could be seen as an expression where live-like SPL's are attained with headroom to spare, and thus "overkill" is not really overkill but rather what's necessitated to acquire sufficient, or at least some degree of headroom. For that to happen you need way more than the required output power to reach a given max. SPL, but many if not most operate with what's merely enough for a certain SPL ceiling, therefore failing to understand the importance of headroom. 

Of course it goes to show that more output power alone is not the only, let alone best way to attain headroom; we need efficiency as well to make the most of those wattages if thermal compression is to be taken seriously (which it must), but I guess that's for another discussion.  

+1 @phusis 

@tcutter what are you using to high pass your speakers at 80 hz? I’m interested in doing the same thing. I want to relieve my speakers of some of that bass and open up my amp options. Thanks.

I love how @phusis refutes my claim, and then in a couple of paragraphs refutes himself.  Hahahaha, have at it guys, I've said my peace.