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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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Showing 2 responses by rwbadley

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. 
rwbadley's avatar
rwbadley
143 posts
 
I wouldn’t advocate against the use of REW or other methods of DSP available if you have them. 
If you are attempting to dial in your sub to a system, phasing does have some importance, maybe especially for odd room acoustics or multi sub environments. 

I found the utilization of a sub/main sound wave null measurement at the listening position for a particular set of frequencies near crossover point,  then reversing polarity of the main speakers didn’t achieve the anticipated result. I used two identical dB meters, and varied the locations taking notes. I don’t have a perfect listening room, that was quite obvious. 
I found at the lowest apparent dB a general agreement, then main speaker phase reversal  would indeed show an approximate ‘highest output’  but the ‘walk around’ test still felt somewhat disjointed. 
After retrying this with an ear also to the timing of impact, I found an interesting thing that slightly shorter sub delay (I’d have to guess of several msec) built a more cohesive setup- both at the listening position and from various parts of the room and in the adjacent areas. 
This was using several types of recordings with dynamic sharp impact at an appropriate low Hz level output as called for in the situation. 
One would think it not to be so critical maybe especially using several subs. But this was the way I approached setup after finding the other methods to not quite nail it. 
It’s obviously only a suggestion to those trying to dial in using the sub/speaker bass null method that they may also find a slightly shorter (or maybe longer, depending) delay to attain the desired result. Cheers,
RW
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