building diffusors. ... out of wood?

[dynomike]

Hey.

I'm just starting into a control room reno project and I'm looking at some diffusion options.

I was thinking about building a bunch of diffusors for the rear ceiling / mid-rear side walls and was thinking of how to make some out of wood. A million cuts of different thicknesses and depths could work with a tablesaw, no? I've seen at joao's studio (www.joaocarvalhomastering.com) they have a bunch of cool diffusors made of large wood dowels and others out of various 1-2" thick rectangular boards sticking out of the back wall. Any ideas how to make these easy / cheap?

-Mike

[Professor]

Boy the one you check out is boring compared to this George Massenburg masterpiece...



There's a nice little article about it in the last Digizine (with Bjork on the cover) or just check it out here.
The idea is that with enough diffusion there is no need for absorption.
Pretty cool.

-Jeremy

[Rigsby]

Holy fuck.

[Professor]

Yep, that was about how I responded too.

And then I felt bad for the guy who has to do the dusting.

-J

[mjau]

And then I felt bad for the guy who has to do the dusting.

-J

Just had the same thought. That's insane.

[dynomike]

And then I felt bad for the guy who has to do the dusting.

Oh intern!? Man thats nuts.. no I only mention Joaos diffusors because it looks like something borderline attainable... thats a martin pilchner studio.

-mike

[Professor]

Funny, I thought this looked like a pretty straight-forward design.
Time-consuming to be sure, and probably heavy, and all sorts of other issues.
But most other diffusors rely on formulaic math while this relies on randomness. Other diffusors also plan on bouncing sound waves into absorbers while the intent there is to diffuse into diffusion into more diffusion.

I kind of figure that you could scale the concept to simpler designs to suit your needs.
For example, if you take 2" x 2" tines instead of 1x1, and just use pressure treated wood with the slightly rounded corners instead of cutting sharp corners of cabinet grade stuff then that would be a good start. Then choose a shallower depth like ranges of length from 4" to 12" deep at 1/4" intervals, you just need to cut enough for each panel.
If you cut 12" x 12" squares of 3/4" plywood then you need 36 tines per square foot. You could mount them with a single countersunk screw through the ply into the tine, and then if necessary build a small frame around the base of the square. (No, I haven't built one, I'm just trying to think through how I'd do a simpler version.)
I think that if you had a table saw, a power drill, and a weekend then you could probably put together a lot panels. Of course, if you figure on covering the 500-600 square feet of wall space they have done, it might take longer.

I don't know, I guess I'd just really like to see how people interpret that design into home-brew varieties.

-Jeremy

[Rod Gervais]

And then I felt bad for the guy who has to do the dusting.

-J

Just had the same thought. That's insane.

J,

isn't it though?

Actually - one of the reasons it works is the rooms sheer size - you figure it's 24,300 c.f in volume..... and that helps a lot.

George Massenburg is a pretty shaprp fellow - has a great mind to work out that room.

By the way - room size does matter with a strictly diffusive approach -

Mike- just hw big is this room of yours?

Sincerely,

Rod

[dynomike]

I'm definately not looking at straight up diffusion.. the room isn't that big. 9.5 feet x 22 feet.. less than ideal, but I have my console and speakers set up at one end of the room (not at the walls, but you know, speakers 4 feet out from front wall.. it works well) , so I'll need to do a bunch of absorbtion on the front wall and whatnot. But as I said, I'd like to add some diffusion further back to overcome the deadness which encourages me to mix a tad bright.

[Rod Gervais]

I'm definately not looking at straight up diffusion.. the room isn't that big. 9.5 feet x 22 feet.. less than ideal, but I have my console and speakers set up at one end of the room (not at the walls, but you know, speakers 4 feet out from front wall.. it works well) , so I'll need to do a bunch of absorbtion on the front wall and whatnot. But as I said, I'd like to add some diffusion further back to overcome the deadness which encourages me to mix a tad bright.

Mike,

with a room 22' deep, your ears should be around 8'-4" from the front wall - (38%) which places you far enough from the rear wall that diffusion would be a nice benifit.

I would hesitate (however) placing these on the mid-side walls - they are going to end up right in your ears - just think about it for a minute-

The center of your head is sitting 4' - 7 1/2" fromthe side wall - if your diffusor is only 12" deep- then you only have roughly 3'- 2" from the face of the diffusor to your ears......... that is really much closer than I would ever reccomend.......

Sincerely,

Rod

[dynomike]

Thanks Rod.. Yeah I wasn't thinking of putting them that close. Or having them a foot deep except perhaps on the back wall. More like, back 1/3 of the side walls.

But really, has anyone built their own diffusors? Cheap ideas? I realize I *could* chop up a shitload of 2x2s and screw them into a piece of plywood (for mounting) but it would probably look awful.

[Scodiddly]

Supposedly you can find some good plans at the BBC's website, but it's been a while since I've seen any reference to it. It's possible to scale stuff differently, but in general it's supposed to work a lot better if you do the "Quadratic Residue" approach to the actual length ratios and layout.

Bear in mind that it's probably going to be heavy, and you need a good way to mount it.

[Professor]

Agreed, for a room so narrow you're not going to want thick diffusors on the side walls, but you wouldn't want just 2-4" of absorption at the sides either since that would only clamp down on highs, while your lows would still be giving you standing waves. In particular you would have a standing wave at about 60Hz and each linear multiple upward - 120, 180, etc. And of course, those are too low for absorption without maybe a foot worth of material or more.
You may want to look into the design of Helmholtz resonant absorbers to see if you can do those along the side walls. Or you could go with an angled diffusor that reflects the side walls head of or behind your listening position as much as possible. Obviously audio coming from some directions would be bounced back at you, but your main concern would be first reflections and those potential standing waves.

-Jeremy

[lg]

that's gotta be one of the slickest uses of a horrible material i've ever seen.

[klangtone]

You may want to look into the design of Helmholtz resonant absorbers to see if you can do those along the side walls.

I just came from AES and attended a couple panels on acoustic design for small rooms. Helmholtz resonators were getting a bad rep because they are rather inefficient (they take up a lot of space and you need a lot of them to be effective). Also, you may tune them for a particular frequency, but then the temperature and humidity changes and the frequency changes too! And to make matters even worse, by the time you put the resonators in the room, you've sufficiently changed the dimensions of the room to change the standing wave frequency you designed the thing for in the first place! Ugh! So, unless you really know what you're doing, you probably don't want to build a helmoholtz resonator.

Roy