"Jim Lesurf" wrote in message
...
In article , Serge Auckland
wrote:

You put everything into the 'sig' of the posting so I had to fiddle about
the rescue it for the following:


Ak! I can't have that I'm afraid. I think I understand what you're
saying, but what I'm saying is that loudspeakers are non-linear loads
and something


Loudspeakers are *not* in any way non-linear loads.

Erm... IIUC that isn't correct. 'Dynamic' (i.e. coil and magnet) speakers
have distinct nonlinearities. e.g. the inductance of the coil is affected
by its surroundings and the interaction varies with displacement. I have a
feeling there are JAES papers on this stemming from ideas about changing
from voltage drive to current drive. IIRC There is also a similar effect
in
terms of the back EMF varying with the changing field coupling. I think
this can be measured as current waveform effects.

However that does not change the basis of using the voltage input to the
speaker for setting levels when doing an amp comparison as any speaker
nonlinearity will be 'common mode'. If you are using the same speaker to
compare two amps, either they are (un)affected by the above in the
(audibly) same way, or not.

Jim, as befits an academic, is of course correct in saying that there are
non-linearities, but as far as I know these are secondary if not tertiary
effects which are swamped by the mechanical non-linearities of a
loudspeaker. The variation in load impedance with displacement is of such a
low level that, in engineering terms if not in academic terms, can be safely
ignored. Jim, if you have some figures that are at odds with this view, I
would be interested to know them.


S.

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