Basic question about impedance and watts

I just bought a pair of Thiel cs3.5's and am now looking for an amp. If the impedance is 4Ohms (i think this is the correct value, i didn't get the owners manual) and the recommended power is 50-150 watts (once again, a guess), how much power should the amp have? Do i need an amp that is 50-150 watts at 8ohms, or do i need an amp that is 25-75 watts at 8Ohms (assuming the amps watts double as the impedance halves)?
I guess the reason i had no luck searching for this is because its so basic.
if anyone knows the specs for these speakers, could you let me know? the owners manuals are available on Thiel's website for most, if not all, models except the 3.5s.
First of all, you can't assume that "the amps watts double as the impedance halves." Some do, most don't. Second, there's no standard technical meaning for "recommended power," so every manufacturer probably means somethng different. (If I were a speaker manufacturer, I'd assume that most consumers only look at 8-ohm power ratings, so I'd use 8-ohm power ratings for my power recommendation, even if they were 4-ohm speakers.)

I'd e-mail Thiel and ask them what they recommend in terms of amp power for that model, and whether they mean into 8 ohms or 4 ohms.
Ketchup, it's really not that critical, but I'd err towards the higher power side if you have a large room and like to crank it up now and then. If I recall, I think the 3.5s use active bass equalization, and if that's the case, the bass will tend to drain a lot of power from the amp...

Did they come with any kind of electronics that plug into an AC outlet?
they did come with the bass EQ that you mentioned, and it does plug into AC. when i hook it up, a hum/static comes out of both speakers. i got a little bit of a deal because of this, hoping that thiel could fix the unit at a reasonable cost. i've only heard great things about their service, even if the 10 year warranty is up. we'll see!
anyway, i will call them tomorrow and ask about the eq and their power recommendtion.
if amp produces 50W to 8Ohms than to 4 ohms it should double the output current or have a transformer's secondary coil stable to 4 Ohms.
Not neccessarily the wattage will double. The output power is rather dictated by peak capabilities of the output devices.
I've heard great things about Thiel's service as well. Good luck to you!
1-you should get as much wattage as you can afford. Thiels will suck your amp dry. Don't get me wrong, I love thiels. However, anyone buying that level of speaker must match it with an equal amp.
2-a little help with wattage:
Doubling the power will get you a 3db gain
Every 10db will double the perceived listening volume
Therefore, a 94db speaker, 8ohms, will produce about 110db at 50watts. An 87db speaker will require about 150 watts to get the same volume.
model CS3.5
Bandwidth (-3dB) 20Hz-22KHz
Amplitude Response 23Hz-20KHz +/- 2 dB
Phase Response minimum +/- 10 dgrees
Time Response minimum +/- 50uS
Sensitivity 89dB @ 1 watt-meter
Impedance 4 ohms
Recommended Power 50-250 watts
Size 33 X 33 X 107 cm
Weight 77 pounds

When I questioned Jim Thiel about the power recommendations he said that they were given with high quality (amps that could "double down") solid state (standard 8 Ohm) power ratings in mind, and that as such one should double those ratings if they chose to use tubes. Your power requirements will depend on your listening room and desired volume. Bottom line, the absolute minimum amp should be capable of providing 100 watts into 4 Ohms. IMHO you would be best served using a quality (quatliy is the operative word) amp capable of at least 200 watts into 4 Ohms. Plato is right on with regard to the equalizer!
BTW, Thiel recommended a least 1 foot from a rear wall, 3 feet from the side walls, and 8 feet from the listener, set up in an equilateral triangle as a start. Thiel also suggested that 3 feet from the back wall, 5 feet from the side walls, and 10 feet from the listener would be preferable.
Thiel also suggested quality cables tightly connected.
Thiel's customer service is second to none!
Good luck.
Thanks for all the info, guys!
I called Thiel today and spoke to some very nice people. They told me that if I send the EQ box back to them, Jim Thiel himself will test and repair it at no cost. They're also going to send me a copy of the original owner's manual, and they even offered to send me spikes if I didn't get them with the speakers. This made my day!
If anyone knows of any amp companies this helpful I will buy their stuff, but I doubt there are any with customer service this good.
All of the info that you guys provided above matches what Sherry (of Thiel) told me today, such as the amp needing to double down, the EQ box sucking up power, and needing quality cables.
I thought she said they needed 50-350 Watts, though, but I must not have heard correctly. Whatever she did say, (250 or 350) she added that they have used much more powerful amps with great results... so I guess 350W should work :)
Unsound, I'm assuming you have 3.5's? Can you offer any more advice on amps, such as what brands work well with them? I'm already going over my budget and was hoping to only spend about $500 on an amp (used), but if I absolutely have to spend more I guess I will.
Ketchup, no I don't own the 3.5's. Your Thiels deserve a real quality amp. When they were new they were often paired with amps in excess of $3K. Your budget is a'hem, challenging. Here on Audiogon there are a couple of Aragon 4004's for sale, an older Threshold, an older Classe' and what I would personaly recommend (albeit a bit more money) a brand new Sonographe. Good luck.
Can I ask one more question? Is a Bryston 3B considered quality, and could it work for me? I guess that was 2 questions. I'm not exactly sure how old it is, but hopefully the 20 year warranty is still good.

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.
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.

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

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.
Bombaywalla, you've got the idea. I think it was NAD, maybe 20 years ago, that was really pushing this concept. It does make some sense for budget gear. Of course there are no free rides and you rareley see more ambitious products touting this concept, even if they are capable of it.
Try Nad,clean, and very musical...the c370 is in your ballpark..more than enough power for Thiels...I use the c350 with 4 ohm loads...and believe is very loud in my 16 x 20 room...good luck...
I've found Aragon's customer service to be as good as Thiel's. Also, the laid back sound should take the "bite" off of the thiels nicely.
With all due respect to Elevick, I believe that Mondial the parent company for Aragon has recently been bought by Harmon. Judging by the previous comments posted here on Audiogon, I think it's fair to say that Harmon's reputation for customer service has been less than sterling. While Harmon may make a special case with these higher-end products, only time will tell and I think that untill further notice there may be more risk to owning Mondial products than previous owners may be accustomed to.
Sorry Unsound...Mondial Designs was purchased by Klipsch, not Harmon. How that has affected their customer service is a question I cannot answer.
Goinbroke, thanks for the correction. That might be better than being under the Harmon umbrella.