# Phase Cancellation at Crossover Frequency



## mdalehts (Mar 22, 2013)

Please help, and please re-direct me if this question as been already been addressed.

The setup: 3.2 ht/audio system with L/C/R speakers and two sealed subwoofers (no presence or surrounds). The L/C/R speakers match each other, and the subs match each other. The auto-calibration program sets all speakers to "large" and confirmed that all speakers are in phase. I visually inspected and tested each speaker to verify their positive polarity. The mains are connected to a two-channel power amp; the center via the AVR's center channel port; and the subs via the AVR's dual mono LFE ports.

The problem: When the mains are set to "large," and the subwoofer phase in the AVR is set to normal, the SPL is great! However, when the mains are set to "small," the room loses a lot of SPL unless the subwoofer phase in the AVR is reversed – which then improves the SPL but not to the extent of the original large/normal setting. Also, at the small/reverse setting, the SPL gets worse as the crossover in the AVR is raised. At the large/normal setting, the SPL improves at the higher crossover setting.

The question: I want to set the mains to "small," as recommended on this and other forums, but the system seems to fight itself at this setting. What might be the problem? Thank you for your consideration.


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## robbo266317 (Sep 22, 2008)

It sounds like a typical phase issue with between the sub and the amp. 
If you can only do the sub in phase or out of phase, ie no phase knob on the sub, then I would try connecting the sub up out of phase and run auto calibration again.
If you have the equipment it would be good to run REW to get a better picture of what is happening. 
http://www.hometheatershack.com/roomeq/


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## mdalehts (Mar 22, 2013)

Thank you, Robbo. The phase adjustment on the subs is variable. I will run the auto-calibration with the phase adjustment on the subs in reverse and see what happens. I don't yet have REW, though that might be my next venture!


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