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Re: [all] stereo to mono phase problems



Hi Paul,

> I've experienced the phase problem with a variety of sources and isolated
it
> to a problem  between the mixer and the amp + speakers. The mixer is an
> Alesis32. Monitoring through the mixers headphone output does not exhibit
> the same muddy result when panning to center.

If you're convinced it's your mixer-to-speakers connections you can
certainly check them for correct phasing.  Depending on your amp and
speakers, it's relatively simple to check them.

First, get a ohmmeter or continuity checker (or something that functions
like one).

Next, confirm that the left and right mixer-to-amp cables are wired
identically.  For example, for 1/4" phone plugs confirm that if the left
cable goes tip-to-tip and shield-to-shield, then the right cable does also.
Note that for correct phasing, the absolute pin-to-pin connections do not
matter, but the cables must be identical.  That is, the left cable could be
tip-to-shield so long as the right cable does too.

Third, perform the same check on the speaker cables.

If the cables check out, you might want to check for improperly wired
speakers.  The cheapest way to do this is with a battery and a resistor (to
limit the current).  I usually use my ohmmeter.  It's possible to zap your
speakers so be careful.  Remove the speaker grill so you can see or feel 
the
cone or tweeter.  BRIEFLY tap the speaker connections with the
battery/resistor and note the direction of cone/tweeter travel (in or out).
Repeat with the same polarity on the other speaker.  The travel direction
must be the same.

If everything checks out, that leaves phase reversal in the amp.  This is
not very likely in a commercial amp.  However, some amps have phase
inversions switches for bridging and other purposes.  Check for such
switches.

> I have ruled out the source as the problem. The source is fine when
patched
> directly to the amp (hence no panning to center). Is panning to center
> inherently going ot cause a phase problem. Could it be the room or 
>speaker
> position causing a problem? The source is either mono tracks from a
digital
> multitrack deck, CDs, DJ-600 mixer output or mic input.

If I'm understanding you correctly, you patched a stereo source directly to
the amp.  This will not show up the phasing problems you described.  If you
have a source-to-mixer phasing problem (by far the likeliest culprit) the
problem will show up when you electrically combine the left and right
channels.  I would not expect to hear it when the stereo source is patched
directly to the amp inputs.

Also, if the signal goes through an effect loop, that can mess with the
phase as well.

Hope this helps.

Dennis Leas
-------------------
dennis@mdbs.com