Room size vs the absorber/diffuser debate.

[took-the-red-pill]

First, thanks for the site John, and all you who donate time to making sure our studios aren't complete disasters.

This will be a question about the back wall of my control room. I will post the dimensions of my room as well as acoustic treatment I've done so far, but first the questions.

I've heard it said several times that 'in a small room, use absorbers instead of diffusers. Fair enough, but I've yet to find some actual sizes to determine which would be better for my room.

1-What would you say is the 'cutoff point' where a room becomes too small to benefit from diffusion?

2-I've so far treated my room only with absorbtion, and plenty of it. The room is getting pretty dead and will only get more so as I set corner absorbers on the floor. Based on the following information on my room, would some diffusion work well on that back wall?

3-Are there any special considerations that might trip me up in this situation?

This is the diffuser I was considering building:

http://www.pmerecords.com/Diffusor.cfm

Room dimensions:
*16'L X 13'W X an average of 9 1/2' high(6/12 vaulted ceiling).
*The side walls are skewed, narrow at the front and wider at the back.
*The room is perfectly symmetrical.
*The monitors are soffit mounted.
*The front and back walls are parallel to each other.
*The front wall has a 4' X 4' window in the middle of it to the outside world.(I live way out in the sticks and have a soft spot for natural light. The view is incredible out here.)

My head at mix position will be about 6 feet from the front wall-since that is the distance between my monitors. This of course means I will be 10 feet from the back wall.

Acoustic treatment I've done so far:

Walls:

*There are 6-2' X 4' X 3" panels filled with Roxul AFB, 3 hung along each wall to cover first reflections. BTW I have mounted them about 3" away from the walls.

Corner absorbers:

*All ceiling to wall corners are treated with similar 2 X 4 panels. On these I stuffed the space BEHIND each corner panel with AFB as well.

*2-16" wide X 8' high panels vertically in the rear wall corners, also with AFB stuffed in the cavity behind them.

*There are 4 front corner absorbers, 18" high X 4' wide and about 2' deep stuffed with Roxul AFB. These are in the top and bottom corners of the walls I built to soffitt mount the speakers.

Ceiling:
The following are all stuffed with 3" Roxul AFB, are hung by chains, and have a 3-4" gap behind them.
*1- 4 X 4 panel over mix position.
*2- 16" X 8' long.
*1- 2' X 8'.

*I'll be building a 4 or 5 more panels, also stuffed with 3" roxul AFB to set along the bottom corners where the walls meet the floor. These will be movable.

So as you can see, I have only absorbers so far and would like to diffuse things a bit so the room doesn't become completely dead. Maybe dead is a good thing, but I don't think so from what I've read.

Thanks for your input.

Cheers
Keith

[carsten_d]

howdy keith,

I guess my answer won't help you much 'cause I can't tell you what is "true", "good", "bad" or "false".
I struggeled a lot on this topic, too and came to the conclusion that I must give it a try. regardless what
science, people or "common use" say.
my room has nearly the same size and it was like a miracle when I installed my selfbuilt diffuser
(though I can't tell if it's "good" 'cause I haven't listened and tested enough right now).

there's a really cool thread on gearslutz about diffusers

I used qrdude for the calculations
also some great tech infos on this site: go to technical overview. (sorry, no direct link)

when you think the diffuser sucks in your ctrl room than you have a really cool tool for your rec room.
so you can't go wrong in building one =)

my room felt a little too dead after all this tons of rockwool absorber stuff installations (about
3msec RT 60 measured with roomeqwizard) and it was like wearing battens all the time. although listening
to music was extremely great. I could hear all the different nuances in reverberations and rooms in songs
I listened to since ages but wasn't aware that they were there...anyhow...it was a little annoying and
exhausting over a longer listening session.
that's why I thought I should give it a try. and it feels good. but it still has to approve.

btw. I built a 7n+1 QRD diffuser with 5 periods. the fourth is inverted (look for Barker Code)

FYI some pics

greetings and good luck,
carsten

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[Ethan Winer]

I've heard it said several times that 'in a small room, use absorbers instead of diffusers. Fair enough, but I've yet to find some actual sizes to determine which would be better for my room.

The conventional wisdom is that diffusors need space for the diffused reflections to "develop." I think the general rule is you need one foot of distance for each inch of well depth. But my own experiments show that diffusion can be useful in small rooms and at much closer distances. Even when only a foot or two behind your head on the rear wall, diffusion sounds infinitely better to me than a bare wall. This video lets you hear what various diffusor types sound like very close:

All About Diffusion

And this video lets you hear a smallish room (11.5 by 16 feet) loaded up with diffusors all around:

Hearing is Believing

As I see it, the main problem with diffusors is they're expensive, whether you buy commercial products or DIY. If the cost or effort to DIY is not an issue, I say go for it.

--Ethan