Placement of Diffusors

[naethoven]

What is the rule for the distance you need to be away from your diffusors? I read on this site a good average rule of thumb was approx 1ft away for every 1 inch the diffusor is deep. That makes since for mix position and back wall placement, but what about wall placement in the studio proper? I you build a 16" deep dif to be wall mounted, are you required to play 16ft away from it to avoid comb filtering? Even if the room is 32ft long, you could only stand right in the center. That doesn't make much sense. Also, in Master Handbook of Acoustics, there are plenty of pics of high end studios with QRDs what looks to be only 3 or 4 feet away from the mix pos. What's the deal?
Thanks

Nathan Webb

[Jeffrey Hedback]

You want to have 8' min between mix chair and diffusors so that the return energy is coherent. Any shorter and you're much better off with thick absorption panels.

There's no "need" to have diffusion on rear wall and there are still competing theories if that surface should be diffused at all.

My preference is a hemisherical diffusor rather than QRD (like RPG Hemi & Auralex SpaceArray)...you really don't "hear" it as diffusion, but it does (referring to rear wall application) enhance mid detail (500Hz to 2KHz) and consistent response throughout room.

[Ethan Winer]

Originally Posted by Jeffrey Hedback

You want to have 8' min between mix chair and diffusors so that the return energy is coherent. Any shorter and you're much better off with thick absorption panels.

I used to agree with that conventional wisdom, but I've since changed my opinion after experimenting with QRD type diffusion very close. I don't like diffusors at reflection points, but almost anywhere else sounds very good to me. Even two or three feet behind the listening position. I think it'd be great for a bunch of us to get together in person to experiment further with this.

--Ethan

[Glenn Kuras]

Ethan,
I agree that it would still work but for best results you want 1' for every 1" of depth of the diffuser. Rules are made to be broken, but then again there are other things that can be used like absorption when close to the boundary.

[Jeffrey Hedback]

Hey Ethan,

I do not disagree at all that it is possible to use diffusion (QRD included certainly) with very short span to rear wall...just that the pitfalls can be deal breakers.

LEDE concept is certainly in development and the project studio world is an interesting front...where the walls are typically light-duty construction that allow greater LF to pass I too have been successful with diffusion on rear wall (meaning shorter distance). Per your findings, this is a very interesting frontier.

But when greater mass "studio" walls are at play and the LF & Lo-Mid energy is more pronouced, I would go with just absorption...UNLESS I can integrate the diffusion with proper trapping.

[Glenn Kuras]

BTW here is a great article written by Jeff on diffusion.
Diffusion is a Wonderful Tool by Jeff Hedback

[naethoven]

Originally Posted by Glenn Kuras

Ethan,
I agree that it would still work but for best results you want 1' for every 1" of depth of the diffuser. Rules are made to be broken, but then again there are other things that can be used like absorption when close to the boundary.

So, what's the case with a 16" deep diffuser in a 32' wide room Glen? It seems really illogical that you could only put the mic RIGHT in the center of the room. And can someone PLEASE explain the pics in MHofA showing QRDs very close to mix position??

I'm really looking for a mathematic answer here.

[Jeffrey Hedback]

Naethoven,

Back to your original question (and we've covered the mix room application)...I see that you're talking about the "studio proper" or tracking room.

The answer is more simple: there are no rules...the goal being an inspiring space to perform and accurately capture performance. Through that perspective diffusion can (and has) be used in every manner imaginable: 2-3 feet away on walls, on ceiling high above, on ceiling suspend lower, on one wall, on parallel walls (offset between walls).

You need to know: obviously how big the space is, the type of applications, the true performance spec/characteristic of your diffusor(s) & all surface finishes including absorptive panels.

Attached is space I did where diffusors are inches from ride cymbal...sounds beautiful. Client uses Royer Stereo Fig 8 mic...no phase concerns.

Does this help explain the pics you've seen in MHOA?

[Ethan Winer]

See Posts #16 and #17 here:

Can a room treated for mixing be a good drum room

I'd say the same applies for a mix room.

--Ethan

[naethoven]

I am in the process of constructing a small commercial studio, and I'm just trying to do treatment research before I get to the point of installing it. At this point I am almost finished with framing, and in the process of designing the HVAC. My previous thread was a sticky in the "Studio construction" forum, titled "Angles of CR Walls". If you scroll all the way to the last few posts, you can see my floor plan and room sizes. (I'd post it here but I don't have it with me right now.) My walls are double walls, each with 2 layers of 5/8" drywall w/ Green Glue btwn. I plan to diffuse to the lowest frequency I can, I have about 18" max depth to work with.

My main concerns are:
1) If I put an 18" diffusor on the back wall of my CR and put the client seating about 2ft from the back wall (6" from diffusor), it may sound great at mix position, but will it sound distorted at the client seat?

2) If I put 9" deep (or greater) diffusors on all walls/ ceiling of live room, will the sound be distorted due to the closeness of the musicians?

I appreciate all your input. I see what you guys are saying in the pics you posted about the diffusers being close and sounding great, but Jeff why the rule about 8' away that you mentioned? Glen, why the 1' to 1" rule if these placements sound good?

Are there any BBC reports that explain this?

[Glenn Kuras]

See the following to see if it answers your question.

GIK Acoustics presents "How Diffusion Works!"