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Author Topic: phase cancellation  (Read 1133 times)

Randall Petty

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phase cancellation
« on: June 07, 2007, 12:38:07 am »

I have a question about the possibility of interference between a wedge monitor and a small guitar amp.  My wedge used to be slightly to my left/front with the small guitar amp on the right, pointed at my right ear.   Due to stage space constraints the wedge is now in front of me but to the right.  It seems that now the sound from one is interferring with the other -- or appears that way due to the left ear hardly participating.

I agree that an in-ear monitoring solution is better and hopefully we'll be able to move towards that.  For now, perhaps I should move the guitar amp behind  ( and slightly to left of me ).  I never intended for this 15 watt tube amp to point at the congregation, but there isn't room to put it on my left pointing at my left ear.       To clarify, my guitar signal makes it's way into both the wedge and the amp, with the wedge/PA portion having either some delay, chorus or both on it.
thanks
Randy Petty
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Tom Young

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Re: phase cancellation
« Reply #1 on: June 07, 2007, 06:45:22 am »

Phase cancellation does occur when the same signal is applied to more than one loudspeaker and these signals are combined (at your ears) at the same level but there is a timing difference. The timing difference is from physical distances plus any electronic delay that either signal is subjected to. This phase behavior is frequency dependent. As you move your head (in any direction) the cancellation frequencies shift. If you moved much closer to one source (wedge or guitar ldspkr) the phasing would be reduced significantly because the levels are no longer anywhere near equal and (to a lesser extent) the timing difference has increased.

Solution: stop using two monitor sources. It is most practical to move the guitar cabinet away from you (without turing it up) and use the stage monitor as the primary monitor reference. Or as you said: use IEM's.
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Tom Young, Church Sound section moderator
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Ira White

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Re: phase cancellation
« Reply #2 on: June 07, 2007, 08:30:49 am »

Though you might expect some phase cancellation, it shouldn't necessarily be that predominant. I don't hear many complaining about phase problems between monitors and stage instrumentation.

You might have a wedge amplifier hooked up out-of-phase that is compounding the problem. Check your amp and reverse phase if necessary to see if that helps with the interaction of the two.
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Ira White
Sanctuary Sound, Inc.

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