Damping factor or watts?

It's interesting to note that the highly regarded Pass X350, X600 and X1000 all have damping factors well below 100. Thanks, Duke, for your insight.

Audikinesis

DF=1 is a little extreme. On the other hand Atma-Spere design does not have transformers and capacitors in the signal path !!!. I would stay away from amps with DF>500. Icepower, I use, is a different beast and has inherently high DF (speaker always connected to V+ and GND - only direction changes). In addition TIM is a result of the charge traped on the junction of output transistors when overdiven momentarily - does not happen in Icepower.

Some amps with high DF (suggesting deep feedback) don't sound harsh or bright but make you tired after a while. It is because our brain fills the gaps when amp is choked-up after transitions (TIM). I would stay away from very good spects - something has to give. TIM was uknown 40 years ago!

As I remember, long long time ago 16 Ohm or even 32 Ohm speakers were typical and damping was easier. Lower impedance came with solid state's (I suspect) desire for higher power. Also, underhung speakers (narrow coil in wide gap) are rare inspite of their lower distortions - is it cost?

I agree with Duke - amplifier damping is secondary to box and woofer selection...by a long way...it does not surprise me that pro drivers with underhung coils would sound tight as the woofer is always fully in control of the amp as Atmasphere describes (sees full force of the drive signal throughout its excursion and therefore behaves in a very linear fashion). Poorly controlled woofers with long coils in narrow gaps will be less well controlled no matter what amp they are connected to (as the coil moves in and out of the linear portion of the magnetic field they see less drive signal).

An under damped speaker may gain from a higher damping factor (10 or so), however a critically damped or over damped speaker is unlikely to benefit much from damping factor (it becomes a moot point as the mechanical behavior dominates).

However, a low damping factor (or high output impedance) coupled with a speaker with a large swing in impedance will certainly tend to emphasize the "peaks" in the speaker impedance response (often resonance for a woofer but a port can change this).

When under damped speakers have a typical bass hump in frequency and also have a high impedance at their resonance then a low damping factor amp will almost certainly give you bass bloom as both factors discussed above may combine to give much stronger bass.