Fixing a null at MLP

greg90 · Aug 8, 2024

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 · Aug 8, 2024

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.

greg90 · Aug 8, 2024

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.

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 · Aug 8, 2024

greg90 said:
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?

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

greg90 · Aug 8, 2024

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.

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

Todd Anderson · Aug 8, 2024

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)?

greg90 · Aug 8, 2024

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)?

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 · Aug 8, 2024

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.

greg90 · Aug 8, 2024

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.

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 · Aug 9, 2024

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?

greg90 · Aug 9, 2024

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?

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.

Todd Anderson · Aug 9, 2024

Just in looking at some room simulations... with your couch 14 ft off the front wall, you can get a pretty decent response with the sub placed here...

And if you add in a second sub, here, you get a nice lift and smoother predicted response...

Todd Anderson · Aug 9, 2024

Here's a sim of single sub with the couch 13ft off the front wall...

Todd Anderson · Aug 9, 2024

Try that placement in your room and see what kind of response you can measure. Microphone pointed toward the ceiling, placed at ear level at the middle listening position.

The simulation can't predict your room exactly, for obvious reasons... and perhaps you've already tried your sub there?

Travis Ballstadt · Aug 9, 2024

Todd Anderson said:
Just in looking at some room simulations... with your couch 14 ft off the front wall, you can get a pretty decent response with the sub placed here...

And if you add in a second sub, here, you get a nice lift and smoother predicted response...

Noting the first post, I do believe he has two subs already, both placed along the front wall. He's considered adding a 3rd smaller sub in the rear of the room.

greg90 · Aug 9, 2024

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

Sonnie Parker · Aug 9, 2024

Are the drivers firing up? I would try to fire one of them into the corner.

You can also try changing the distance on just one of the subs... make it 5ft (or 5ms) farther away.

I know that might sound a little wonky, but it can work and you'll never notice that small of a timing difference.

Todd Anderson · Aug 9, 2024

greg90 said:
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

Argh… my bad. I totally blew that one!

greg90 · Aug 10, 2024

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 · Aug 11, 2024

greg90 said:
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

Nice job there greg90

greg90 · Aug 11, 2024

Gerry Iaria said:
Nice job there greg90

Thank you!

Todd Anderson · Aug 12, 2024

Excellent. Glad you're getting some improvement!

Fixing a null at MLP

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