Bass Null and phase? - Home Theater Forum and Systems -

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post #1 of 10 Old 01-08-12, 07:52 PM Thread Starter
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Bass Null and phase?

Hi all,

I'm having an issue with my sub bass. Today was the first time I fired up my subs and I noticed a really bad null in the exact spot I will be sitting (figures!). My subs are in a fixed location (powered by one plate amp) and cannot be moved. I have two 10" subs per side (each pair shares air space). I do have and will continue to add acoustic treatments. My question is, will wiring one set of subs out of phase have an effect on this null?

I would normally just do the test, but it's a lot of work to pull the subs out of the wall and wanted to know if the work is worth the trouble.


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post #2 of 10 Old 01-09-12, 12:28 AM
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Re: Bass Null and phase?

A sketch of your room including distances to seating position/Sub location and room lengths will give a better starting point to decide what can be done to improve your setup..


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post #3 of 10 Old 01-09-12, 09:08 AM
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Re: Bass Null and phase?

I would not recommend wiring them out of phase. I would first recommend moving your seating position since the speakers cannot be moved.


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post #4 of 10 Old 01-09-12, 01:02 PM
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Re: Bass Null and phase?

Chances are reversing the phase on one set of subs would make things even worse. You really need to post up a set of response graphs showing how things are in your room.
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post #5 of 10 Old 01-09-12, 05:17 PM
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Re: Bass Null and phase?

So let me see if I have this correct. You have 2 separate subs, both in different locations. Both separate subs have a pair of dual 10" woofers.

You should never wire subs out of phase when they are in the same enclosure, I don't think that was your question but just in case. There could be phase cancellation issues, I had that problem with 1 sub located on the front wall and the other on the back wall. When measuring I had a big null so I reversed polarity on the back sub and immediately I could feel the difference in bass using test signals.

If your running full range speakers your subs could both be out of phase with your mains as well. I was listening at a friends house with full range speakers to music without his subs. The bass was nice but when he added in the subs the bass was noticeably less so I knew right away there was a phase issue. We reversed phase on both of his subs and the difference was huge.
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post #6 of 10 Old 01-09-12, 05:40 PM Thread Starter
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Re: Bass Null and phase?

My seats are fixed. They were purchased from a closing Cineplex and are bolted to the floor. So I really have no adjustments other than treatments, equalization and wiring.

My room is rectangular. The dimensions are 15ft long, 11ft wide and just under 7 ft high. My listening position is 4ft back from the rear wall. The null effects all of the front row.

I do plan on doing measurements once I get a PC.

I am going to try to run one set of subs out of phase, just to see what happens. Nothing to lose right!

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post #7 of 10 Old 01-09-12, 06:39 PM Thread Starter
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Re: Bass Null and phase?

I just switched the phase on one subwoofer. No change. The null extends to both side walls and is about 3ft wide. In this area, almost no bass is heard or felt.

Last edited by f0zz; 01-09-12 at 06:47 PM.
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post #8 of 10 Old 01-11-12, 01:26 PM
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Re: Bass Null and phase?

Hey fozz,

The fact is that most square or rectangular rooms have the same problem, a bass “hole” in the center of the room, that decreases the closer you move towards any boundary.

Unfortunately there is no easy solution. Traps will certainly help, if you get enough of them. Another option would be to load up with enough additional subs to “overwhelm” the “ hole” and get adequate bass for those seats in it. But of course, in your situation that will mean the bass for your back row(s) will probably be too strong.


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post #9 of 10 Old 01-11-12, 04:15 PM Thread Starter
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Re: Bass Null and phase?

The funny thing about this null is it is from wall to wall. The entire front row is getting pretty much the same bass response. Even with you head against the side wall bass is substantially reduced when compared to the rest of the room.

I am doing my best to get some measurement of my room. The REW software looks complicated, and I'm not particularly computer savvy.

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post #10 of 10 Old 01-12-12, 06:30 PM Thread Starter
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Re: Bass Null and phase?

Would a possible fix be to move two of the subwoofers to the opposite wall of the room? The subs would be facing each other.
Not sure if this would solve the problem or cause more. I would still have only one amp. So I would not be able to manipulate their responses.

Also not sure what it would be like to have a set of 10" woofers behind me (above the listeners heads)?

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