Basic question about impedance and watts

Ketchup,

IMHO, Elvick is the only one who seems to have gone thru a bit of number crunching to give you some idea of what kind of power you need for your Thiels. Suffice it to say that you need a *brute* of an amp that "doubles down"!

These days there is a large influx of Class-D power amps on the market. There was a thread called "Green Mountain owners please read" just a few days ago so it should be on the 1st page of the Amps/Preamp or Speaker forum. Therein they were discussing the new Panasonic $600 power amp (I think that I'm remembering this correctly) that many user's considered to be one heck of an amp. Do read that thread as this amp *could* work for you wattage-wise & budget-wise.

To give you an estimate of power required:-
89dB @ 1m using 1W input
implies 80dB SPL at 9.9 feet from speaker.
implies 90dB SPL at 9.9 feet needs 10W (10dB increase implies 10X the power)
implies 100dB SPL at 9.9 feet needs 100W
implies 103dB SPL at 9.9 feet needs 200W
implies 106dB SPL at 9.9 feet needs 400W
implies 109dB SPL at 9.9 feet needs 800W
This is using just 1 speaker. Using 2 speakers, just add 3dB to each of the above numbers.

If you are listening to a Chopin piece (for example), there are very quiet passages then suddenly the piano takes off easily creating transients that are 109dB SPL. Your amp would need to provide 400W/ch momentarily IFFFF you want to get a perception of reality/live-event.
At the min. you should have a high current 100W amp with a 3dB dynamic headroom (this is going to cost you!). However, it appears from the discussion from above mentioned thread that this Panasonic class-D amp is a killer amp.

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&

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.