Basic question about impedance and watts

thanks, Bombaywalla.
what do you mean by a 3dB dynamic headroom? are you referring to a particular amps ability to double its wattage going from 8 to 4 ohms?

Ketchup, while its not my first choice, I do like the Bryston 3B ST. As I said before, while the Thiels appreciate as much power as they can get, depending on your room and desired listening levels, I think a really top quality solid state amp rated at 100 watts into 8 Ohms that can double down is the place to start. The Thiel 3.5's are not very forgiving of abberations in the upper registers and can be a touch soft in the upper bass/lower mid range and a bit on the forward side.
They require the proverbial iron fist in a velvet glove.

Ketchup,

Dynamic Headroom of an amp is the amp's ability to double it's power output wattage while KEEPING THE SPEAKER IMP. CONSTANT!
i.e. 100W into 8 Ohms can become 200W into 8 Ohms momentarily (a few milli seconds).
This requires a honking power supply in the amp (or a new paradigm for a power supply as evidenced by the new class-D power amps).

Do check out the possibility of use of the Panasonic SA-XR25/45 receivers, which are 5-ch amps. The SA-XR10 is another possibility & $100 cheaper.

http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1072721930&read&3&4&

Bombaywalla, I thought dynamic headroom was in reference to an amps ability to increse its typical steady state power output for brief moments.

Unsound,

I *think* that I know where you are coming from: if we have a 100W amp then 100W is the max. output power whereas the user usually never uses 100W. This is your line of thinking. Am I right?

ASSUMING I understood your line of reasoning: if we have a 100W amp & we want 90dB SPL @ 9.9 ft then we need 10W. We are using 10% of the total power. If we need to put out 100dB SPL, the amp has the reserve (as it is a 100W amp) so we are not yet tapping into its dynamic headroom. We are simply using the amp within its power rating.

Now what happens if we need to create 103dB SPL? We will need 200W! Where's that going to come from? The amp is already operating at max output power of 100W to create 100dB SPL.
Well, if this amp has 3dB dynamic headroom then it'll be able to put out 200W momentarily.
Dynamic Headroom always refers to an amp's max. power rating because within the amp's power rating there is no need to tap into the dynamic headroom i.e. you can use the amp within its rated spec.
The concept of "headroom" always refers to going beyond the max. rated spec (& NOT the steady-state power UNLESS your steady-state power consumption is at the amp's limit! Very rarely! However, we do have some head-bangers amongst us). You'll see the same for tape decks (atleast my Denon tape-deck does).
Hope this clarifies some.