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Author Topic: Diffusers and Room Size  (Read 3646 times)

ustompsteve

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Diffusers and Room Size
« on: August 23, 2006, 03:08:44 pm »

Can a room be too small for diffusers to work effectively? I am thinking of the QRD type diffusers in a small bedroom studio.

--steve
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franman

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Re: Diffusers and Room Size
« Reply #1 on: August 23, 2006, 03:20:21 pm »

This is a bigger question than it appears to be. You will get many opinions about this. The classic LEDE design (and the modified RFZ Designs that we use) are based on a certain amount of time passing after the direct sound from the speakers hits your ears, before any reflected or diffused sound returns to the listening position. Generally this ITG Initial Time Gap is accepted to be between 20 -25msec. This would call for a distance Delta of at least 22 feet (speed of sound x time).... In other words, you would want the ROUND TRIP to be at least 22 feet for the sound to travel past your ears, hit the diffusors (or other reflective/diffuse surfaces) and travel back to your ears... So, any diffusors much closer than 11 feet behind you can be too close...

Now, that's not to say we've never put diffusors into smaller time intervals. If I have a smallish (control) room and I want to put diffusors behind the listening position less that 10 feet from my head, I use a moderate amount of 2D diffusions, such as Omnifussors or Skylines, instead of the 1D QRD style. THe reason is you get more scattering with the 2D guys, and as such a little more attentuation (not as much level) coming back. AND, it Sound Good To Me (SGTM --- I'll use that a lot).

Hope this helps.
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Les Ismore

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Re: Diffusers and Room Size
« Reply #2 on: August 23, 2006, 04:55:46 pm »

Hi Fran, Welcome to the place!
I used to have a LEDE studio that I ran commercialy for 14 years. I closed down a few years ago and have recently soundproofed a room on the bottom floor of my house now to stuff my gear into.
I did not have enough room to build angles into it so I just built floating walls inside of the existing room. It is 20' x 9' x 7' high. It's pretty much all parallel walls unfortunately. It is absolutely packed with gear including a 2" machine and console and 15" Tannoys.
I feel that the best I can do with a tiny room like this is to absorb absorb absorb. The floors are carpeted and I am starting to think about 2" fiberglass board on the walls and maybe a few tube traps in the corners.
I don't think diffusion would be appropriate in an environment as small as this.
Would you agree with this? Do  you have any opinions on small square rooms like this?
I realize of course it will never be a great sounding room, but with house prices going the way they've been going recently I cannot justify building a proper room into the house and devaluing it that way in case we wanted to sell.
Thanks for your thoughts,
Les
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franman

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Re: Diffusers and Room Size
« Reply #3 on: August 23, 2006, 06:18:57 pm »

Les Ismore wrote on Wed, 23 August 2006 15:55

Hi Fran, Welcome to the place!
I used to have a LEDE studio that I ran commercialy for 14 years. I closed down a few years ago and have recently soundproofed a room on the bottom floor of my house now to stuff my gear into.
I did not have enough room to build angles into it so I just built floating walls inside of the existing room. It is 20' x 9' x 7' high. It's pretty much all parallel walls unfortunately. It is absolutely packed with gear including a 2" machine and console and 15" Tannoys.

Les


Les, when you are "fighting" with a small, rectangular room (which isn't necessarily a bad thing) the biggest battle is room modes and speaker boundary interference which will mess with you low end response at the listening position. It's beyond the scope of this reply, but a proper study of the room dimensions, and speaker position is required to ensure you will have decent bass response at the mix position.

Depending on your configuration and how far the mix position is away from the rear wall, diffusors may be helpful.
1. Avoid letting the mix position fall into the middle of the front-to-rear dimension. Usually we are in the middle of the side-to-side dimension, and this is correct for symmetry, but try to avoid being in the middle of the other two dimensions, as this is a spot where there will almost certainly be odd bass response.
2. What is the distance from your mix position to the rear wall?? If it's over 10 ft (in front of the mid point in the room) then QRD style diffusors can be helpful.
3. Cover the areas in the front of the room (side walls and ceiling) with at least 4" of rigid fiberglass absorption to control early first reflections.....

make sense??
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Les Ismore

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Re: Diffusers and Room Size
« Reply #4 on: August 24, 2006, 05:21:01 pm »

Yes it makes perfect sense. Unfortunately this is what my room kind of looks like (excuse the crappy drawing)index.php/fa/3309/0/
The dimensions are 9' wide x 20' long x 7'6" ceilings, carpet on floor. Try as I might this is the only functionable way to lay the gear out in the room. I would have much rather layed it out in the other direction and not had it up against the wall, but my console and speakers take up 10' of width and the rooms only 9' wide. It just don't fit any other way.
My big 15" Tannoys are on top of outboard gear racks and then I've got more outboard on top of them right up to the ceiling. the floor rack in the picture only goes up to about 3' high. My nearfeilds are on the console meter bridge, backing to the wall.
Any suggestions how to minimize the inherent problems? Right now it's all reflective so I am going to start treating with absoritive materials. Your suggestion of 4" fiberglass over 2" is greatly appreciated. Any other thoughts? What about acoustic foam intead of fiberglass?
Thanks very much for your responses.
Les
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franman

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Re: Diffusers and Room Size
« Reply #5 on: August 25, 2006, 04:08:21 pm »

Les,

I can't see your drawing... but what you have to do is try and find a spot to install some base trapping..broadband stuff... to tame the LF in the room. This can't hurt. This is almost another thread as we are off the diffusors and room size issue.

I will try and make a post soon with some generic ideas for broadband bass traps. keep your eyes out...
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fmdesign.com
griffinaudiousa.com

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