Ineed some help with a simple math equation

The difference in gain will not affect how much power can be supplied to the speakers.  It will just affect the positions of the volume control that you would find yourself using (and a 3 db difference is not a great deal), and the position of the volume control at which the amp reaches its power limit.

Regarding 500 watts vs. 400 watts, that is a difference of only 0.97 db, which corresponds to a volume difference that is barely perceivable.

Regards,
-- Al
 

Perceived loudness change can be calculated as:

k^(1/3.5)    where k is a ratio of powers.

(500/400)^(1/3.5) = 1.066  (6.6% increase).
I doubt that you can hear that.  

You want "better".  If you need more sensitivity you will be 2.03dB "better" with 29dB/400W

Better measurements IMHO are distortion and noise in the actual usable range. If you have spec sheets, look at the THD+N in the 30-100 W range.

However, inefficient speakers are less sensitive to noise, and many doubt we can hear anything below 0.5%, so absolute numbers below that may e meaningless.

Best,

E

Also important to understand how they eat power. Are they low impedance ? Difficult to drive due to high phase angle or low Z in the bass?

You may indeed need a very solid amp, but not necessarily need all those rated watts at 8 ohms.

Best,

E

As a Thiel 3.6 owner I wholeheartedly agree the more power the better (those speakers are excellent at high level transients, which is probably why they need power).

My suggestion: since the Thiels have an average impedance of less than three ohms from mid bass to 20khz, go with the amplifier that has the highest 4 ohm power rating at 1000 hz. (I assume those power specs are at 8 ohms).

bill10907 and gs5556

good to read that both of you guys enjoy Thiel speakers.
Please check out and join in the Thiel Owners Thread discussion
(under Speakers section). We all would enjoy reading about your Audio gear and musical journeys.

Happy Listening!

Your preamp will likely breath a little easier with the 400w/29dB gain amp if the amp's input impedance is equal on both amps. 

Almarg, Kijanki, eric_squires, gs5556, Jafant, bpoletti. Thanks for weighing in. I appreciate it, as I have a decent technical mind, but with sound and waves I'd say I'm out to lunch. Plus, I think the math just got harder. Here is some more info. The 400 and 500 is at 4 ohms. One is a classe amp CA-2200 (400 with 100K input impedance). The other amp is Pass Labs X250.5 (500 with 20K input impedance). My room is 20 x 24 and carpeted. I have the room set up with speakers at 5ft from the back wall and about 5ft from each side wall. The room has three windows, each covered with a matchstick blind as a difuser. Each side window is also protected by a 2x3 absorber hanging from the ceiling to block first reflection waves.
The pre is an ARC Ref 3. After the system and my ears are warmed up, I can take the "loudness" to 75%, after that, I think the sound starts to.... say, break apart a bit. So with the Pass, I'm hoping for 1. a slightly better amp and 2. just a little push in the "snap" (e.g., drumstick on drum skin), such as what you get with live music, at home when your stereo is loud enough, but without the distortion you get with live music (usually venue dependent).

Bill,

Re: your last paragraph, the source has a lot to do with those sound attributes. Usually a DAC or cartridge with superior resolution and detail (but not of the hashy sounding "false-resolution" variety) will deliver on that.  Also, I find that listening at lower volumes with such sources is equally, or more, satisfying and involving compared to lesser resolving sources at higher volumes, making the criticality of ultimate power (but not quality) from my amplifier to deliver eardrum-rattling SPLs less important.  

Dave

Dave,
I agree. I play vinyl using a Clearaudio Stradivari II cartridge on a their Performance SE via an ARC PH8. I want music from my main system is a physical in-your-chest experience.

I find this very interesting; although I have custom speakers, me and the crossover engineer used the sound of top of the line Thiel speakers mated with an ARC amp as a model for the sound.

I find this very interesting; although I have custom speakers, me and the crossover engineer used the sound of top of the line Thiel speakers mated with an ARC amp as a model for the sound.

I have no idea what went wrong twice .  That's supposed to read,   "we used the sound of top of the line Thiel speakers mated with ARC amp as a model for the sound.