What do you look for in damping factor?

Around two or three is good. No, I'm not kidding!

Like others suggested, I suspect a high or low damping factor is likely neither good nor it is bad, rather it may render an amplifier more or less suited for a given speaker. For example, while Sean has commented elsewhere on this forums that he found the Vienna Mahlers always to display a sloppy bass, I listened repeatedly to these speakers at the recent Denver AudioFest, and found them to have an extremely deep tight and tuneful bass while being driven by a Rowland 312. I then checked the damping factor of this amp and found it to be a wapping 1000. One possible explanation of the apparent 312/Mahler high synergy is that the Mahlers have a fairly low impedance of 6Ohms, dipping to 3 Ohms in the bass. This relative low and uneven impedance likely requires a high damping factor, which is found in the 312.

Damping factor plays a role in system performance, just not a large one.

Damping factors above about 15 or 20 to 1 will result in no audible improvement, but such amplifiers that do have such damping factors have proven themselves incapable of playing definition and body in bass instruments, and for that matter punch is a problem too. IOW things get worse.

This is because such amplifiers employ large amounts of feedback to this effect. Feedback, while lowering output impedance, simultaneously restricts dynamic peaks and impact. Additionally as Duke mentioned above, odd-ordered harmonics that the ear uses as loudness cues are actually enhanced, causing an amp with feedback to be harsher.

The solution is less feedback.

We do perceive a different phenomena as the output impedance of the power amplifier is raised, and approaches that of the speaker- the amplifier will make more distortion.

We have words for this type of distortion (in order of increasing distortion): warmth, bloom, fatness, turgid and finally, muddy.

So the trick is to have an amplifier that ideally has at least 4:1 over the speaker in use. For a 4 ohm speaker this puts the amplifier output impedance at about 1 ohm, 0.5 ohms is likely to be near ideal.

Note that the output power of the amplifier is what places the diaphragm of the speaker at any position in space that it is capable of. The idea that the speaker diaphragm 'falls' back to zero and can ring really does not happen- the speaker diaphragm is powered to full excursion and then powered back to zero- power is on the driver at all times.

Due to this reality, damping plays a minor role.

Ralph, I am slightly confused. Are you trying to say that:

A. The perceivable synergy of the Rowland 312 and the Mahlers exists in spite of the amps high damping factor?

B. The 312's damping factor is immaterial to its synergy with speakers in general.

C. The perceived extreme degree of synergy between the two devices cannot be, and is likely a case of self delusion on my part?

By the way, if I recall correctly, the output impedance of the 312 is 100K Ohms.

The numbers Paulfolbrecht quotes are typical of many good tube amps; if (as others say) you just chase a high DF spec. you are going to eliminate quite a few good amps. I'm using VTL's with my Maggies and the DF is certainly under 5 (they sound great.)