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Critical subwoofer tip

I assume that everyone already knows the importance of phase matching a sub to the main speakers but it’s a little more complicated than simple 90 degrees or 180. The B&W sub that I have has four choices. In every case there has been a definite correct position that can be non standard. My current setup shined at 270 degrees vs the std positions. It’s completely obvious and the other choices would not have been satisfying. 
From my lengthy experience I would want a subwoofer with several phase choices. I personally don’t see how one could seamlessly integrate the mains and the sub without this flexibility. No one asked but i thought this info might be useful to anyone purchasing a subwoofer. YMMV
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ieales's avatar
ieales
1,201 posts
 
Not unless the slope of the cutoffs for both are the same.
Not true. One can achieve near perfect integration with a main 1st and 3rd order sub with polarity inverted.

Slopes must be adjustable. Ideally on both the main and the sub. They do not have to match.

Subwoofer phase adjustments are simply (very small) timing delays applied to ONE of two speakers attempting to producing the SAME frequencies.
Not unless phase adjustment is done with a delay or by physically moving the speaker.

Lastly, one cannot "invert the phase." This makes no sense. Adjusting the phase 90 degrees, 180 or 270 of a subwoofer is adding a small delay in the timing of the sound wave. There is no way to do the opposite and speed the sound wave up, hence no such thing as, "inverted phase."
A typical phase control does not add delay. It shifts the phase relationship in the speaker range. If one inverts polarity, the phase shifts. The timing remains the same.
erik_squires
16,237 posts
 
Adding a sub perfectly to an existing system involves all of the challenges that crossover design has, with perhaps the only exception that you are involved in line level vs. speaker level settings. This is why I say it is far too much for the average audiophile, and best left to ARC systems like built into JL Audio subs or top notch digital preamps or integrateds like from Anthem.

Even if you do all the filtering right, the matter of the room remains.  To paraphrase the Bard:

Aye, and there is the rub, for in that room what sounds may come must give us pause and make cowards of us all.



Best,

Erik
sj00884's avatar
sj00884
80 posts
 
The YouTube test was really useful. Flushed out a level issue but phase was in sync.  The localization of low frequencies as suggested by MC was quite profound in its absence IMO.
mapman's avatar
mapman
22,341 posts
 
Yes doing anything perfectly is always very hard but with the right sub to fit your system, a sound meter app on a smartphone and streamed white noise, doing it very well is not hard at all.

If you do that versus merely doing it by ear you might be surprised about the difference. 

also the more subs to integrate the harder it will be to get it perfect. That’s basic math. Well enough is always much less difficult.
rwbadley's avatar
rwbadley
143 posts
 
In my experience adjusting subwoofer phase matching to the mains using a fixed sine wave/null points was vexing. 
It was much too room and location dependent. 
I found a better result in my system by playing a repetitive kick drum and trying to match the beat sharper than softer. It seems more likely to result in a phase structure that is consistent from ‘the other room’. If you have inaccurate phasing, when you go elsewhere in the house it seems much more apparent. 
If you get this kick drum right, it seems more correct. Not just from the listening position that has room issues effecting it, but from a broader area of the structure. 
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