Using REW to adjust subwoofer phase. - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 18 Old 05-22-19, 10:14 PM Thread Starter
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Using REW to adjust subwoofer phase.

I was just thinking (scary...) it might be useful to be able to adjust sub integration in real time. What I mean is to have the mic at the listening position, your computer running REW near the sub, send 10-250hz pink noise through the appropriate channel(s) covering the speakers you are trying to match with the sub and the sub. REW would then have a real time graph, perhaps a bar chart with 24 bars per octave that you could monitor as you fiddled with the phase control on the sub.

Does something like this exist in REW and I am not aware of it?

Is it a reasonable idea?

I could do something similar with a sound analyzer app on a tablet, but the mic in the tablet isn't calibrated and I couldn't easily have the mic in the listening position while fiddling with the phase control. Perhaps I could cast the app to the TV, but still I have no idea how good the mic in the tablet is.

Right now I run a REW analysis pass, adjust the phase and run again, until I get tired of fiddling or it looks good.

One of my issues is I actually have a sub, and then my DIY mains each have an OB woofer cabinet with a "sub amp" driving the woofers so I have 3-8 times the fiddling depending on how pedantic I want to get.

Interested in what others think of my half baked idea.
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post #2 of 18 Old 05-23-19, 09:06 AM
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Re: Using REW to adjust subwoofer phase.

Sure, use pink periodic noise on the generator and monitor the response on the RTA with these settings:

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post #3 of 18 Old 06-02-19, 12:52 AM Thread Starter
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Re: Using REW to adjust subwoofer phase.

Thanks. It worked like a champ.

My mains use a GR Research OB powered woofer cabinet with two 12" drivers powered by a servo controlled plate amp. The mid & tweeter assemblies are of my own "design" which has an L-Pad for the tweeter, so there are a lot of controls which impact the sound. Using the twiddle - test - twiddle method really was not getting things dialed in very well. Using this method I spent about 20 minutes per speaker and voila, it was done.

Now I need to use the same methodology on the Rythmic Audio 15" Main sub dialed to dial it in with the rest of the system.

Thanks again.

Last edited by aceinc; 06-02-19 at 12:55 AM. Reason: grammar
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post #4 of 18 Old 06-05-19, 07:20 PM
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Re: Using REW to adjust subwoofer phase.

Sorry to ask a newbie question but what does a good RTA graph look like when doing this? When do I know my sub phase knob is in the right spot?


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post #5 of 18 Old 06-05-19, 09:19 PM Thread Starter
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Re: Using REW to adjust subwoofer phase.

Remember my use above is a little different than traditional sub integration.

I saw a dip in the frequencies in the 140-200 hz when the phase was "wrong" and as I changed the phase (rotated the phase knob) I was able to see the dip flatten out. I also used the gain control on the plate amp to bring the entire 15-140hz area up to the level of the rest of the "speaker."

When I use it for the actual sub in my system, I expect to see the same results but at lower frequencies. If I can get to it in the next few days, I'll "detune" one of my speakers, do some screen grabs of the graph before & after tuning.
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post #6 of 18 Old 06-05-19, 11:13 PM
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Re: Using REW to adjust subwoofer phase.

That makes sense. Feels too simple!

Would be fascinating to see the screen grabs.


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post #7 of 18 Old 06-06-19, 06:56 PM Thread Starter
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Re: Using REW to adjust subwoofer phase.

Here is an example the first image is out of phase, the second in phase.

https://www.hometheatershack.com/for...1&d=1559865243
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Using REW to adjust subwoofer phase.-wrongphase.jpg  

Using REW to adjust subwoofer phase.-rightphase.jpg  

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post #8 of 18 Old 06-06-19, 09:46 PM
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Re: Using REW to adjust subwoofer phase.

Awesome. Almost TOO easy to see. Thanks.


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post #9 of 18 Old 07-03-19, 10:40 AM
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Re: Using REW to adjust subwoofer phase.

When you are doing this test. Where do I set the mic at? Where I sit at when Iím watching a movie? I have two subs and one is next to the left speaker and the other one I want to place it next to the sofa as a end table or should I place it next to the right speaker?


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post #10 of 18 Old 07-03-19, 12:23 PM
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Re: Using REW to adjust subwoofer phase.

Quote:
aceinc wrote: View Post
I was just thinking (scary...) it might be useful to be able to adjust sub integration in real time. What I mean is to have the mic at the listening position, your computer running REW near the sub, send 10-250hz pink noise through the appropriate channel(s) covering the speakers you are trying to match with the sub and the sub. REW would then have a real time graph, perhaps a bar chart with 24 bars per octave that you could monitor as you fiddled with the phase control on the sub.

Does something like this exist in REW and I am not aware of it?

Is it a reasonable idea? .... .
FWIW, I did a sweep of the sub by itself and a sweep of each individual main.
I then went into the OVERLAY Phase window and placed the vertical cursor at the SUB/Mains XO point (my case 40HZ).
I then enabled FDW (Frequency Dependent Windowing) and removed smoothing.
I then wrapped and unwrapped all phase plots (mains and sub) so they would be replotted and aligned at the Sub/Main XO point.
I then read the phase of each speaker at the XO point and then used that information to adjust the phase on the sub.
I put the sub's phase half way between my left and right main's phase (split the difference).

This gave me more control than just +/- 180 degrees. The sub is now within @ +/- 8 degrees of each of the mains.

You can then verify the results with a combined sweep to see the summing/nulling/smearing at the XO point.

You can also repeat the procedure to make sure the sub's phase moved in the direction and amount you intended it to (since the sub's phase knobs are usually coarsely marked).

There maybe better ways of doing it, but this is the procedure I used.

HTH
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Last edited by ths61; 07-03-19 at 12:41 PM.
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