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Discussion Starter · #1 ·
Somewhat new to REW. Have the technical issues figured out but still struggle with interpreting things. First graph shows my subs (in green) and my subs plus mains. Thought the frequency dip between 70-80 may have been a phase issue so I adjusted phase on the subs. The second chart shows this. Obviously not a phase issue.

Any thoughts would be appreciated. Overall, I think I have fairly decent looking frequency response. Got lucky I guess because room has no treatment etc. All I have done so far is to have REQ auto eq with a house curve which I imported into the Minidsp.

BTW, I am running three subs. One Definitive Tech Prosub 1000 and two Polk DSW600. The DT is in the front right corner of room and the DSW600s are stacked in the left rear corner of room (plan on replacing these as time and $ permit). I mention this to explain why there is a big drop off below 30. Subs just don't have the oomph. Interestingly, my Polk RTiA9s (being run as large front with no crossover) appear to have some oomph below 30.
 

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What do you get with both subs and mains crossed over at 80Hz? 100Hz? What do the mains look like alone? How about separate phase plots for the subs and mains?
 

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Discussion Starter · #3 ·
Subs are run off LFE outs from Yamaha. Believe that is crossed over at 90 with no way to adjust. Mains are being run as Large from with no crossover at all.

I don't have a graph of just the mains, but don't recall any dips. Will run and post tonight.

Pardon my ignorance, but what is a phase plot?
 

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Subs are run off LFE outs from Yamaha. Believe that is crossed over at 90 with no way to adjust. Mains are being run as Large from with no crossover at all.

I don't have a graph of just the mains, but don't recall any dips. Will run and post tonight.

Pardon my ignorance, but what is a phase plot?
It's a plot of the phase response only, kind of hard to do accurately, so don't worry about it. But if you have smooth response from the mains and subs alone, but dips when they combine, it's obviously an interaction issue. You might consider running these:

With crossover and mains settings as you have them now:
Mains alone
Subs alone
Mains with front sub
Mains with rear subs
Mains with both subs

Then try mains with the same crossover point as the subs, and do all that again.
The results should lead you to the issue. Ideally you'd want to run these at several mic positions and combine them, but that's a lot of work. This should tell you what you need to know.

A phase plot would show you the phase response of something. The phase relationship most people identify with is when you flip speaker connections around, which results in a 180 degree change. The whole phase story is much more than that. Phase represents a timing relationship between a reference and a measured device, with zero degrees being identical to the reference. Phase measurements can show any relationship from zero to plus or minus any amount, though it gets tricky beyond 360 degrees because of the way REW displays phase, unless you use the unwrap function, which is more than you probably wanted to know. Speakers don't have a flat phase response, it's actually a curve caused by the crossover, the box, the driver, etc. And the room gets into the act as well.

What you're probably seeing is an unfortunate interaction between one or the other set of subs and the non-crossed over mains that is caused by the phase response of both fighting each other. There are probably ways around it, but you need more data, or need to experiment more.
 

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Discussion Starter · #5 ·
Ok, understand. I'll have to looking to those plots. It must be an interaction. I'm going to run the plots you suggested. That should help me narrow down what is causing the issue.
 

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Discussion Starter · #6 ·
Ok finally got around to re running all measurements and if it were not for REW I would never have been able to diagnose the problem.

Ended up that flattest frequency response came from setting single Def Tech sub at reverse phase (through Yamaha receiver as the sub doesn't have a phase control) and setting both Polk subs at 270 phase (adjustable at 0, 90, 270, and 360).

Final chart is below. Purple is after adjusting phase of Polks. Green already had phase of Def Tech set to reverse as it was obvious that it was out of phase when set to normal (chart was crazy).

Oh course I could also blame REW for causing me to spend more money as it is now obvious that I have an issue below 30-35Hz. Saving up for a Submersive. :D
 

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