Ineed some help with a simple math equation

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!