Fixing a null at MLP

Ran REW on my subs (on front wall) last night and I have a huge null at 34hz or so. Tried moving subs a little but moving them isn’t really an option. Tried to eq it on rew then on my minidsp 2x4hd. I was able to bring it up some but would have to boost the frequency way too high so I don't want to do that. Used a room mode calculator and have an axial mode around that frequency (not sure if that’s the way to phrase it). Do I try adding a sub to the back wall or more acoustic treatment and bass traps on corners or something else? Currently have panels on my first reflection points for mains and then two on the back wall and two on the front

Travis Ballstadt said:

The best placement for dual subs is in opposing corners. I'm unable to do that, so I have one in the front corner and one about 70% of the way back on the opposite wall. Does a pretty solid job. Unfortunately the best placement for the second sub would be right on top of my desk.

Moving your subs or moving your seating are really the only good ways to get ride of a null. You can use the MiniDSP to improve upon it, first with time and phase alignment, but then with a little EQ. You're right in not wanting to overcorrect with EQ. Unfortunately you're also looking at needing to rearrange the room for best results.

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I can’t move the room much. I have all my seating set up for atmos with in ceiling speakers. Hmm thoughts on adding a couple smaller subs on the back wall and time aligning? Also started looking at hemholtz resonators for that frequency?

Travis Ballstadt said:

Room diagram/dimensions would help, but adding subs at the rear would most definitely be the fastest way to fixing your problem.

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I don’t have any updated pictures with me but it’s rectangle 22L 15.5W 8ft ceilings

Todd Anderson said:

Agree with Travis... your only options are move seating, or add a sub. Pretty much zero chance you can add any sort of treatments to effect any change.

Do you have room in the rear to add a second sub (that matches the sub in the front)?

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i don’t think I’ll able to fit one of them in the back because they are very large and I have to fit an air hockey table back there (for the kids) but I can do some measurements when I get home and see if it will fit underneath. My sub set up is a little different I have them ran in series together and then to one input on the amp. I was kind of hoping I could maybe get a smaller one and put it on the back wall. I will go home and measure my seating as well. I just don’t know how far forward I can go before my front Atmos speakers end up to close to me and my rears too far away.

Travis Ballstadt said:

It might not seem easy, but I'd recommend moving one of your existing subs into the location and take some measurements, make sure that it's going to work before buying anything. It should unless there's something else working against you.

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So I made the move and moved my seating back a foot or so still playing around with sub position. There’s still a null but more gradual and not so deep.

Todd Anderson said:

I would definitely recommend *not* going with a smaller sub to match. That's going to introduce different issues and I think you'll ultimately end up more frustrated.

how far is seating off the front wall?

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I got things moved around last night and ended up getting a lot better response and edited a fairly decent curve in REW(I’m really new to REW) but I need to get my levels higher and do it again. Right now my MLP is 14 feet off the front wall. I moved seating back about a foot for my measurements last night. I also tried measuring a couple feet in front of my original MLP and got a terrible response, but I might try a little closer tonight because I hate pushing my seating so far back.

So I have two subs currently. Right now they are both placed in the center of the front and back wall. I don’t know if I’ll be able to go in the corner because it’s going push my main really far in just because of the enclosure size. Here’s my enclosure for my subs. Two of the same. I have it rear port and downward firing a few inches off the ground

Update. Got a better response. Subs are placed. Middle of front and middle of back about 6” off the wall. Have 1 EQ setting done for my minidsp. Not perfect but huge improvement so far

Gerry Iaria said:

Nice job there greg90

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Thank you!