Nulls at centerline - a physics fact. how to address?

[Watchmaker]

So, I'm pretty slow when it comes to the physics of sound, but it's eventually dawned on me that there will always be a null at the center line of every plane in a room. (*edit: I'm only discussing 1st and 2nd axial modes, way too complicated to think about O&T modes)

Paradoxically, it seems that stereo imaging "requires" symmetry, which is to say, in order to get sharp stereo imaging, one must necessarily also be in the first mode null of the width dimension, at a minimum. Assuming height and depth offsets are possible, one can limit the effect to the null of the width.

Open question: How is this effectively dealt with?

Based on my highly suspect math*, at the mix position I have width nulls at 57Hz and 172Hz and depth nulls at 24 and 72Hz. I can get a good height without significant nulls due to a 9' peak.

* I used Carl Tatz's mode calculator which came up with slightly different results than the algebra of dimension/velocity so I'm going with his formulas though I do not know exactly what they are.

Below is a diagram of my room as it is. My mixes are coming out boomy for fairly obvious reasons and I'd like to improve clarity in the low mids. I have fairly extensive bass trapping and pretty good absorption in the mix space. I could always reference though cans, which I do anyway, but it'd be nice to get the room sounding better.

I am open to reorganizing too, I could put the drums where the mix space is for example...

Anyway, thanks for reading.

[Hugh Robjohns]

...it's eventually dawned on me that there will always be a null at the center line of every plane in a room.

Only if the boundaries are reflective!

Paradoxically, it seems that stereo imaging "requires" symmetry...

It's not a requirement — I've worked in plenty of asymmetrical rooms which had good imaging — but symmetry certainly makes life easier, especially in rooms with little acoustic treatment.

Open question: How is this effectively dealt with?

With broadband acoustic absorbers and bass traps placed intelligently to minimise strong modal reflections at the frequencies of interest. Diffusion can also help for higher frequencies.

Based on my highly suspect math*, at the mix position I have width nulls at 57Hz and 172Hz and depth nulls at 24 and 72Hz.

Sounds plausible...

I have fairly extensive bass trapping and pretty good absorption in the mix space....

They all say that.... but it's rarely true!

[RichardT]

I'm not an expert, my only experience is with treating my own space, but I would try putting a significant amount of trapping directly behind the listening position.

The idea is to reduce the sound getting into and back out of the rest of the room.

And you definitely need more trapping in general.

[Drew Stephenson]

Where you currently have bookcases I would experiment with some broadband trapping. And add a ceiling cloud.
Also more bass trapping - you can say this about almost any home studio.
Except Hugh's

[Watchmaker]

Treatment has been a priority. The bookcases are 80% broadband absorption and 20% SOS magazines providing diffusion.

No doubt there's room for improvement. The Neumann MA-1 app shows a dead zone at ~114Hz, not horrible after that. I probably have a screen capture somewhere but as my studio Mac rarely goes on the web I can't post it for you.

I don't really crank it though so I wonder if I'm really exciting the room dreadfully anyway.

I much appreciate the thoughts.

[Watchmaker]

Open question: How is this effectively dealt with?

With broadband acoustic absorbers and bass traps placed intelligently to minimise strong modal reflections at the frequencies of interest. Diffusion can also help for higher frequencies.

This is exactly it. I'll have to research a bit more to target a bit lower. I will be moving the desk back a bit and pull the monitors in a bit too...

Thanks again!

[Drew Stephenson]

Yeah, 114Hz would fit with the distance across your listening area. Anything you can do with the ceiling peak to get some deeper bass trapping up there?

[RichardT]

What you say makes me think it's even more likely the boom is coming from the other parts of the room.

A barrier to separate your mixing area from it could make a difference.

[Watchmaker]

Drew - I have a ceiling cloud that's about a 1.2 square meters with 2" Corning 713 and a layer of 1lb/sf limp mass (MLV) floating on top of that. I could easily increase that as I have mad carpentry skills.

Under the monitors (KH80's and HS5's) is a 3/4" plywood case, 15" deep x 100" wide that is layered with 713, a 2" air gap, 713 again, another air gap and MLV stapled along the top edge to a frame. Side walls of the bookcase are 9" with a 1" airgap, 713, air gap, suspended MLV and 713 again.

The "live end" has ~ 30% clouds of differing build design and the back corners have corner traps and another ~30% broadband absorption panels with some diffusion on the side walls. The back wall is 60% windows so not much I can do there. I've been thinking of putting up a beadboard wainscotting to liven up the drywall a bit and maybe some irregular stone veneer to break things up a bit.

Richard - yes, I'm wondering if that's the case. I can certainly hear where reinforcement is occuring as I roll back from the desk... I'm not so good at hearing the null.

Trial and error to find the sweet spot. I'm lucky with this room all in all so I'll tweak it as best I can. I am designing a desk which will move the listening positions back from the front wall from ~48" to 80" which should help with the long dimension.

Cheers!