[Bob Reynolds]

Stumbled across this recently and thought it might be of interest:

http://www.stereophile.com/reference/810/index.html

The thing I found most interesting was that an amplifier with an output impedance of 3 ohms (and higher I assume) will have a frequency response that mirrors the impedance curve of the attached speaker.

[dado5]

it's cool to see all that graphed out.  The deviations are not large (except on the high end of the ML speaker) though, so I doubt they would be audible.

Still, this supports those who say tubes work best with single drivers as these speakers tend to have very tame impedance curves. Triode SE and PP amps are not to difficult to design with an output impedance of less than 3 ohms, but OTL, UL and pentode amps generally need feedback to get their numbers this low.

[Bob Reynolds]

I've read that level differences as small as 0.1dB can be detected, but are not perceived as a level change. Regardless of that being true or not, 1.0dB is audible and all the speakers exhibited deviations of at least that amount. In fact, if we believe the Toole & Olive listening studies, the all the speakers driven by the Sonic Frontiers amp appear to be poorly designed.

I thought the article would be of interest to the many tube fans here. Knowing this information gives you a better handle on speaker selection.

My take on the article is that it is a strong argument for active speakers where the amp/speaker is designed as a system.