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R/E/P => R/E/P Archives => Acoustics in Motion => Topic started by: jetbase on August 23, 2006, 10:48:55 pm

Title: Advice on CR traps, absorbers, etc.
Post by: jetbase on August 23, 2006, 10:48:55 pm
Hi Francis, welcome & great to see your new forum.

I'm building a CR at the moment & would appreciate some input on the acoustics for an accurate listening environment. Basically, I've been given a room (which I've been soundproofing by building inner walls, insulating, etc) which is roughly 5m x 4m x 3.5m in dims.

My idea so far is to build some bass traps, Ethan Wyner style, on the ceiling & possibly on side walls. Maybe I'll build them at reflection points and cover them with absorbant material. I have thick curtains I can draw over the CR window when mixing. The floor is concrete, which I'm planning on putting a timber laminate flooring on.

I can't afford to do anything too elaborate, but would like to know if I'm heading in the right direction or not. Any tips or ideas?


P.S. Hopefully the picture below works - my good mate Greg Simmons helping to put gyprock up.
Title: Re: Advice on CR traps, absorbers, etc.
Post by: jetbase on August 23, 2006, 10:52:11 pm
Here's a picture towards the back of the room. You can see there is a corner cut out of the room for the outside hallway, & the ceiling is lower at the back due to a mezzanine level in the factory. Also, there is an office behind the control room. I might turn this into an amp booth at a later stage.
Title: Re: Advice on CR traps, absorbers, etc.
Post by: franman on August 24, 2006, 12:31:08 pm
The good news: Your room dimensions look respectable.. this should work out okay.

The bad news: we've had problems before with the "cutouts", closets, etc in one corner. They mess up the modal response in at least one dimension and make the room not behave as a rectangle. Same with the loft (possibly)...

I would run the numbers for the max size, min size and average size if you want to be thorough about it.

Yes to the bass traps! The more the better. Also, try loading the corners with porous absoption... as much as you can afford to give away (in space).. We usually "cut" the corners with a framed trap filled with fuzz and framing stuffed with 4" of rigid fiberglass, then cover the whole thing with fabric. There's a lot of bass energy (always) in the corners as you have all the modal activity working in a three way corner, right...

Then next order of business is covering the early first reflections off the front, side walls and ceiling!! After that, it's treat to taste with absorption and diffusion at the rear (assuming you are sitting at least 2.5-3M from the rear wall..

Make sense>>>>

You guys might start to see the pattern here (even after one day online)... we recommend the same things over and over. That's because THEY WORK!

1. Good Room Proportions.
2. Lots of Broadband bass trapping
3. Cover Early First reflections with at least 4" absorption
4. Tune trapping as required....
5. Diffusion where applicable...
Title: Re: Advice on CR traps, absorbers, etc.
Post by: jetbase on August 24, 2006, 07:21:01 pm
Thanks Francis. Interesting about the diffusers needing distance to take effect (which you mention in another thread). I never knew that. Do diffusers that are too close have any negative effects? The reason I ask is, what if I wanted to do any tracking in the control room behind the engineer's position? If I had diffusers on the back wall then this would put the recording area in closer proximity to the diffusers. Also, if the room is under control for monitoring, does this mean it will be under control for recording as well (I'm thinking vocals & acoustic instruments).

One final question. You mention corner trapping. One corner at the front is already a little cut off (you can see this in the first pic I put up). If I just put a trap in the other corner would this be bad in terms of symmetry? How about if I put traps in both corners, but one was thinner than the other?

Title: Re: Advice on CR traps, absorbers, etc.
Post by: franman on August 25, 2006, 04:45:10 pm
The diffusor comments are based on their application in a listening room (playback through monitors).. The application in recording spaces can be different. If you are really close to the diffusors and there is not enough of them, they can cause a wierd phasy return... not good...

BUT a small room that is full of diffuse surfaces can sound really cool!! It becomes very difficult for your brain to determine how big the room is (in the recording) because there aren't any distinct distance cues in the reflections. They are all time smeared and it's pretty neat. Not what I WOULD WANT for a control room, but we often do the small "Diffuse Booth" in a mutliple booth design.

Corner traps... symmetrical is better but put em wherever you can!! The room's LF symmetry is already messed up with the notches in the corners so yes, I would put a thinner trap in if necessary..okay?
Title: Re: Advice on CR traps, absorbers, etc.
Post by: jimmyjazz on August 26, 2006, 12:45:39 am
Fran, can you elaborate on how you might create corner traps in an existing room if major structural renovations aren't possible, and the ugliness of tube traps is intolerable?  I have a room I'm working on in which the most I can imagine doing would be to hang a floor-to-ceiling panel from ceiling-mounted eyehooks.  I could stuff the space behind with R13 or any other common insulation . . . what would you recommend for the panel?  

Would this make an effective trap, or am I tilting at windmills?

My other option would be 6" or more of OC 703 or 705.  Not quite a broadband bass trap, but the absorption would be pretty high, even down below 125 Hz.
Title: Re: Advice on CR traps, absorbers, etc.
Post by: franman on August 27, 2006, 04:22:07 pm
I am preparing a post outlining some of our favorite bass trap constructions.... stay tuned.