goldenpiggy
Member
This is how I answered this question for myself (please correct me if I'm wrong):
The dynamic range in music varies greatly, but a rule of thumb I've seen is ~10LU with 1LU ~ 1.3db soooo - lets just say 12db of padding to be really safe.
I enjoy listening with average DB around 80-85... add to that the head room and it equals 92 - 97db.
Next we examine efficiency of the speakers - mine are 85db at 1W at 1m.
Next we figure out what it would take to get to 97db with my speakers (keeping in mind that we need double the power for every 3db) 88db = 2W, 91db = 4W, 94 = 8W, 97db = 16W ...... at 1 meter, but I don't listen at 1 meter...
So next we need to add the listening distance (wich I believe quadruples the power for double the distance) so at 2M = 64W and at 4M = 256W...
And all of that assumes into 8ohm speakers... (some amps produce 2x power into 4ohm speakers, and some AV receivers actually lose power into 4 ohm speakers).... yadayadayada
Annnnnyyyways - you can see by the quick calculation - to be confident of not having clipping - it's not unreasonable to have a 200W amp or bigger.
I think you nailed it. Most of us crank the volume either for more bass or because the recording has such extreme dynamic range (e.g. classical music.) It obviously takes more power to boogie the LF drivers. Our hearing sensitivity is not linear, and is not nearly as sensitive in the lower octaves, so crank it up even more. As one operates at or below a driver's resonant frequency, it sucks a lot more power -- you're just heating up the voice coil at that point. As much as I don't like to brick wall things, when I do live sound, I'll always use 48dB/oct slope on the sub's high pass for exactly this reason. Go just a few Hz below Fs and it can easily draw 2-3x the power, and before you know it, you're clipping or bottoming out the drivers. But most people usually won't see this in a home environment.
The loading on the speaker enclosure also comes into play. If you're at 1/4 space (in a corner), it'll be louder in the lower octaves than half space (just a back wall in a very wide room), which is like doubling the power in some freq.
Finally, not every speaker behaves like a point source or abides by the -6dB SPL loss with doubling of distance. Line columns (not to be mistaken with line array) work on cylindrical wavefront and (theoretically over certain freq range) only loose half as much over distance. You don't see many line columns in the home though.