In article .com,
wrote:

Jim,

Obviously a 'zero width sound stage' would be impossible except in an
anechoic chamber, all other rooms would have some resonance. The fact my
ESL63s are less than two feet from a hard rear wall is probably the
culprit but there is really no other place to put them.

Indeed. With the ESL63s I use for the main hifi the 'width' for real mono
is equivalent to much less than the width of my head at the plane between
the speakers for most source material. Speakers about 1.5m apart (distance
between their closest corners) and a similar distance from the wall behind
them.

The ESL988s in the AV system give a less well defined image. But there are
various room/layout reasons for that. Different room acoustic, closer to
the far wall, etc, etc. Also dependent on precise location of my head.

FWIW I just did a check and found that a mono DVD of piano music made
a good check for this. Has the advantage that the sound is LPCM 1.0
so should ensure that exactly the same sample series is being used for
left and right.

I guess what I'm really curious about is whether this apparent widening
is a 'fault' or a 'feature' (real improvement) because it is similar to
the effect on stereo recordings that I hear as an improvement. After
listening to the X-DAC for a time then switching back to the Quad, the
sound seems a little compressed and slightly muffled. I just wonder if I
am I being fooled by some artefact that the X-DAC is introducing to make
it sound 'better' or is the fact that instruments are more clearly
defined making the perceived sound stage wider.

Hard to say. It could be an imperfection whose effect you like, or a sign
that the X-DAC is 'better' in some way. I doubt reading up on how DACs work
in principle will help as what you hear probably stems from something else.

For example: It might be that the two DACs have different output impedances
and/or coupling caps. These then might give subtly different responses when
loaded by the amplifier input. Perhaps different for the two channels with
the X-DAC. It only takes a small departure from symmetry to alter the
apparent image for double-mono if you are comparing with a very 'narrow'
symmetric case with a less symmetric one.

I've no idea of the above specific example is relevant in your case, but it
shows that an item that might be 'fine' in some circumstances could be
'different' in others. Thought of it because IIRC MF also produced a
'buffer' stage to follow a source and drive the amp. Some modern amps
seem to have input impedances I'd regard as 'low', thus possibly making any
variations in source output impedance more significant.


Slainte,

Jim

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