chung wrote in messag ...

How accurately do you model the skin
effect and resistive losses? How about the loss tangents of the
dielectric? How close to an ideal transmission line is a pair of wires
side by side?

An S-parameter based cable model, would include all of the above factors and
more.





In the end, you are making many approximations in such calculations.
Whether to approximate the cable with a lumped model or a transmission
line model is a small difference, compared to the large uncertainties in
the rest of the system.

You say that the uncentaninties in the rest of the system are greater
than the differences between a transmission line model, and a crude
components cable model. That is true, in the application you suggested, but
that is not the only possible application for a cable model.





It will be like trying to find an answer to 5 significant digits, when
all your inputs only have 2 significant digits. You are chasing 4th
order effects when you don't even have second order effects under control.
...
Besides, looking at transmission line loading is the wrong way to
analyze such amps.


It was *you*, who in a previous message, suggested using a cable model,
for testing amplifier stability.


Much better to vary the output loading and make sure
that the amp is stable for all possible loads. And you would model that
with resistive, capacitve and inductive loads.

Trust me, no one analyzes the stability of an audio amp by using
transmission line models of cables.


You are the one who suggested using a cable model for testing amplifier
stability.




Why bother?


Because you can't think of any application that requires an accurate cable
model, you think one is not needed. You are being like the man in the
1880's, who suggested closing the US Patent Office, because "all possible
inventions" had already been made.





Suppose you were to write a circuit analysis program based
on quantum mechanics?

It is not necessary. An S-parameter based cable model, already takes into
account *all the factors* that cause cable loss, including quantum effects,
if any.





This
model could be useful for educational perposes, and also would have
some pratical applications.

Not for audio cables or audio amps.

Again, you are being very short sighted.






Would you write a speaker cable model that was "dead on" accurate, or
write a (close approximation) component type model?

See all the approximations above.

The "approximations above" are only for a limited case. They does not prove
there will never be a need for an accurate cable model.

Bob Stantone news:c0439$40143681$c247604