Don Pearce wrote:
You need to think this through a bit.

Perhaps a bit but I would expect you to put in most of the work to
develop your procedure. I am just chatting on usenet and have no
interest in getting directly involved in experiments which have the
objective of convincing audiophiles they are wrong about the sound of
cables and the like.

Do you know how unflat the response of a room is -

Why is it relevant? The objective is to check two sounds are the same.
This is something you can test for in any room.

and how much it varies with even a couple of millimetres of movement?

Again I cannot see the relevance.

Likewise for a microphone.

Why do you need to move the microphone?

What you are
suggesting here could not be done, even in the best anechoic chamber
with the best microphone.

I can see no particular need for an anechoic chamber or a particularly
linear microphone.

And what do you do about the fact (to 99.9999999% certainty) that
there IS no audible difference between the cables to factor out

What has audibility got to do with it? The difference between the
cables is easy to calculate given a few basic measurements.

- what is it that you are actually adding to the signal here?

One way to proceed might be something like this:
* Analyse the two cables for the given amplifier and loudspeaker
impedances.
* Program filter using analysis so that, say, signal via cable B is
transformed to signal via cable A.
* Create sweeps directly and via filter.
* Play unprocessed sweep via A and measure. Play processed sweep via B
and measure. Check an order of magnitude or two closer than difference
between A and B playing unprocessed sweep.
* If not, modify filter parameters guided by difference and repeat.
* Use filter to generate processed music source.
* Switch cables A B, A B, A B,... but play a random sequence of A B and
A B* where B* is the processed source that produces the same signal as
A.
* Ask the subject if the sound is the same or different and analyse for
significance as usual.

Again, I am sure there are a few variations and improvements but the
above is hopefully the gist. Obviously this involves more messing about
than a blind test but it allows the subject to hear both cables in a
fully sighted and "natural" manner. The thing hidden is which source is
being used for one of the cables.