What is wrong with negative feedback?

I'm not sure if DF>100 makes much sense since inductor in series with the woofer has resistance in order of 0.08ohm.

8/0.08=100

Ralph, this is the wrong place to ask, but would you care to answer the math as proposed by:

http://www.transcendentsound.com/amplifier_output_impedance.htm

Just trying to get a grasp on the "how". The other controversial article is not related to this thread.

Fascinating relating electronics to chaos theory. Maybe we can use it to predict long term digital format forecasts.

The math is fine right up the 2nd to last paragraph where an assumption is made that is incorrect. It matters a lot what the output section topology is. An excellent example is the difference between a triode gain stage and a cathode follower using the same triode. The CF will be found to have a lower output impedance, according to Rp/1+mu where Rp is the plate resistance and mu is the 'voltage gain' of the tube.

So if we take the example given we get 17.5/3 = 5.767 (the mu of a 6AS7G is 2), which is for a simple CF circuit. For a Circlotron, which is a CF variant, the formula is similar, the 1 is replaced by a 2 as above so we get 17.5/4 = 4.375

In these cases it is assumed there is no feedback.

It is like a boob job. Too much and you are all over the place.

I don't believe it is fair to talk about damping factor without mention of speaker 'Q'.
A hi DF and a 'Q' of over say....1.3 will still produce sloppy bass as will a very low DF and a critically damped 'Q' of .707
Also, no mention has been made of Voltage source vs Current source amplification, and the speakers which are best suited for each.