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.



On a tangent, I am interested in learning why my valve amplifier sounds
so good. Put simply, if all of this can be measured, why can't some
sort of (distortion?!) filter be used to recreate the sound? The
novelty of the glow has more or less worn off, and if such a thing
existed I'd give it a go.

There are plenty of valve simulators available on the pro market for DAW
plug-ins. They add level-dependent harmonic distortion, some low-level
noise and soft clipping. Some people pass their mix or part of it
through a reel-to-reel recorder to get a similar effect.

That does. however, omit the frequency response changes which arise when a
valve amp design has a high output impedance and the speaker has a load
impedance that varies a lot with frequency.

Some recent reviews I've seen list 'samping factors' down to about 2! I'd
be amazed if that didn't change the results quite audibly with many
speakers. Indeed, it seemed to me to make a subjective review worthless
unless you are going to use the same speakers as the reviewer. (Alas, they
sometimes don't bother to say what speakers they used, which doesn't help
much!)

The above point are examples of why I've personally always been a fan of
people taking o/p impedance measurements more seriously than is normal in
audio mags.

Slainte,

Jim

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