[Ian Iveson]

Nick Gorham wrote

Extending analysis in that direction, dynamic changes in
output impedance, and hence in DF, will lead to dynamic
variation in the amplitude of SPL variations with
frequency. Can that be called distortion? What about the
consequent IMD, arising from both the speaker and the
output stage? That would not be part of the usual
measured IMD of an amp with a sine wave and constant
load, I suppose.


A lot of work was done in the 1950s with regard to DF and
output impedance, there seems to have been a period where
amps were produced with variable DF, ie +ve, zero and -ve
output impedances. Maybe you should read some of the
papers from that period, they were far from groping in the
dark.

Actually they were pretty much groping, mostly, from my
memory.

Perhaps you could help Ian with a summary of what you
learned?

However, as I realised after I posted, *dynamic* variation
in damping factor, i.e. during the wave cycle, adds another
and quite different can of worms.

Ian