Subwoofer setup with REW

[Fredd3]

Hi,
I got myself a pair of subwoofers that I'm trying to setup together with my main speakers. B&W 804d2. Subwoofers are B&W db3d and db4s.

I have started out with just 1 subwoofer the one I got first db4s and try to find proper phase and volume together with my mains.

The orange line is with Main speakers only (sub off)
The green line has phase 270 on subwoofer and is very similar to the measure of mains only, Is that good or bad? Does that suggest it cancels out more than amplifies?

The other traces with 0-180 degrees all seem to add a few db at the lower frequencies. but then drop out some at around 50 Hz.

Overall the 0 degree phase measure seem to have the highest overall SPL. Is that the best one then?

The subwoofer is setup with low pass filter at 120 Hz

 

[Fredd3]

Hi again,
Maybe I figured it out.
Looking at the phase diagram and comparing "no sub" with the 270 phase I see that the lines trace pretty close to each other, which I assume is good. That should mean that the sub and main speakers are in phase?

By comparison the other phases seem far away from the 270 degrees version:

 

[nathan]

That should mean that the sub and main speakers are in phase?

My experience so far has been that looking at the complete sweep (sub and one main speaker) will tell you about phase better. Basically, if the transition region ( from one octave below to one octave above the crossover) looks linear, you've got the phases in agreement.

(That means for an 80 hz crossover, I focus on the 80hz area, but things from 40hz to 160hz are in play because that the outermost audible overlap usually.)

This is however an iterative process...because the crossover selected will also come into play. You might achieve the best linear response not by adjusting phase, but by adjusting the crossover. I once had speakers that could play down to 60 but the most linear interaction with the sub was at 90hz so that is the crossover I selected.

Finally, phase adjustment is sort of a proxy for distance, but they don't always act the same.

So you've got at least three levers to work with (I'm ignoring room placement, but of course that is another, as is listening position).

TLDR: I'd look for a smooth transition region as measured by REW from your listening position, of the sub and a main, as an indication you got it right.

 

[nathan]

I have started out with just 1 subwoofer the one I got first db4s and try to find proper phase and volume together with my mains.

I guess I should note that this is the wrong way to start. The best practice is to get the two subs aligned with one another first, then acting as a single sub, get that single sub integrated with the mains.

 

[Fredd3]

Thanks for you feedback @nathan. I found a very helpful video that explained how to use the phase diagram in REW to figure out if you have the proper phase set on your subwoofer.

At 18 mins they start talking about subwoofer integration. I tried following that and it's sounds pretty good now.

I am however waiting on some new longer cable and when I get them I should be able to move my speakers a little bit and also one subwoofer into a slightly different position. Will redo the messurements then and see what comes out of it.

Any good suggestion on what Hz I should limit my sub at? Currently I set it at 120 Hz.

I have a stereo preamp and no subwoofer outputs there, so cannot set any sub settings or delays in the preamp.

 

[nathan]

At 18 mins they start talking about subwoofer integration. I tried following that and it's sounds pretty good now.

That should be fine. I cannot tell for sure but it appears their demo sub has only two phase options (0, 180) which is very limiting. If you have variable phase as an option on your sub, you can do better.

Any good suggestion on what Hz I should limit my sub at? Currently I set it at 120 Hz.

You mean the low pass filter (might be called "crossover") on the subwoofer itself? Measurements will be the best way to determine this but since you are playing your main speakers full range, I would do a sweep of the subwoofer alone, and your mains alone, and then choose the -3 db point of the mains.

Then, run a sweep with the sub and mains running, and see how smooth that looks. It will probably have a bump up.

So then set the low pass filter on the sub 3hz lower, and try again.

And repeat that until you don't see a bump at the place where the sub and speaker is playing together.

I have a stereo preamp and no subwoofer outputs there, so cannot set any sub settings or delays in the preamp.

This is not horrible. It limits your options a lot, especially with this sub since this sub doesn't have a bass managed line level output. Of course the manual may not be complete (like it doesn't even show a phase button let along knob) so I may be missing or misunderstanding some features of the sub.

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Personally, I'd probably get a MiniDSP 2x4 HD and run the line out from the pre-amp into the miniDSP, which can act as a crossover (sending just high pass filtered audio to your amp + mains, and low pass filtered audio to your sub) and can also set delays (distance) for each sub, aligning them to one another, and then a separate delay (distance setting) for the combine response of the two subs, and then could also tame some room modes with its built in EQ.

But I'm not saying you should or need to go down that rabbit hole for now, simply that in my own person journey, I started with something like what you are describing and ended up with the miniDSP as a solution

 

[Fredygump]

It looks like your main speakers (Orange) extend down close to 20hz, but there is a massive dip at ~65hz. So your mission is to fix that dip.

The region where optimization has the most affect is from 50-120hz. Below that, a typical house's structure acts as an absorber. You can see you have very flat response with your main speakers from 25hz to 45hz.

Without a miniDSP, you will need to experiment. Try all the combinations of phase adjustment on the subs to see what measures best (measurement of all subs at the same time). You should see changes in the combined frequency response measurement as you manipulate the phase settings on the subs. And maybe try crossing the mains at 80 or 100hz. See what affect that has.

Looking at phase is the wrong theory to apply to subwoofers.