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Can hardware change speaker phasing over time??

After years of great listening, I suddenly noticed I wasn't getting the sharp center image with vocals.  I spent hours moving the speakers and even did Room EQ on my Denon receiver (which normally would tell me if speakers are out of phase). The vocals sounded diffuse.  Finally, I switched the wires on one speaker.  BOOM!  Right back to crystal clear center imaging on vocals, on all of my favorite tracks.  I've checked all the wires.  Everything is hooked up right, though now red is hooked to black on one speaker.

Could something have changed the phasing in the hardware?  There is no other place in the set up the wires could have been reversed.  I have triple-checked that the ++++ cable is connected to the red output on the amp.  

Signal goes from Mac Mini by USB to Bryston DAC, by two single channel cables to Denon receiver, by two single channel cables to Parasound A21 Halo amp, by speaker wires (one wire marked ++++) to B&W CM10s.
stroud27612
rixthetrick's avatar
rixthetrick
1,060 posts
 
try another amplifier?
stroud27612 OP
39 posts
 
The mystery deepens! At lunch I hauled up my father’s old Mirage speakers and hooked them up to the full system, wired "in phase", and they sounded and tested as "in phase." So it has to be the B&W speakers.  I put the B&Ws back in the system, and they still only sound "in phase" if wired "out of phase."

Tonight I will hook them up to a different amp and see what happens.

And I have now created a special curse for B&W because you cannot use banana clips on them.
stroud27612 OP
39 posts
 
Listening to the CM10s wired "out of phase" was pleasant and produced good imaging with vocals and the Stereophile test tracks for phase.  But then I noticed I had lost a lot of bass on some songs.  Loss of bass is a side effect of being out of phase.  Wiring the speakers back in phase brought back the bass but lost the great vocal imaging.

So the only logical conclusion is that it's the tweeter or midrange driver on the one speaker that is out of phase from its counterpart.  I plan to test this hypothesis tonight with a bunch of test tones and see which ones sound focused and which ones sound diffused.
stroud27612 OP
39 posts
 
Here we are, six months later, and last night I noticed I could hear and "see" each speaker again.  The vocals were not centered.

I wired the speakers back to "in phase" and the world was right again.  I have a wandering phase issue, either with one of the speakers or the electronics in the receiver or amp.
imhififan's avatar
imhififan
2,108 posts
 
I wired the speakers back to "in phase" and the world was right again. I have a wandering phase issue, either with one of the speakers or the electronics in the receiver or amp.
I suggest you test your B&W CM10s polarity with a 1.5V battery, + to speaker positive and - to negative terminal and see if the woofers "pop" forward. But this test only determine the woofers polarity, in some cases, tweeter or/and mid-range driver could be wired out of phase to its woofers, due to some capacitors in series you need to check the tweeter and mid-range driver at its quick-connect terminals on the crossover.
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