Thanks Ott,
from johnlsayers...
I've revised my design a bit and invite your comments.
Internal dimensions are: H:3030mm W: 4230mm L: 5750mm
Ratios are: H: 1: W: 1.40: L: 1.90
(which is approx. H:10ft, W:14ft, L: 19ft)

Q: Did you angle the ceiling or 3030mm all around?
I'm also interested in this design I found.

Ott responded on 05/27/2013

They are pretty much the same dimensions as my control room. It works great with a nice even spread of modes. The bass response is very predictable.

I built Rockwool bass-traps into each corner - floor to ceiling triangular-section [60mm along the two right-angled sides] and faced off with wooden frames covered in hessian.

I elected not to go for pitched walls and/or ceiling as it made ratios very difficult to calculate and threw all kinds of 'oblique mode' complications into the mix. As this was my first build I wanted to keep things as simple as possible and that paid off, in terms of time, budget and acoustics.

I did build a large flat 'ceiling cloud', 50mm x 25mm timber framed and in-filled with 50mm Rockwool slabs and covered with cloth which appears to make the ceiling slope down from the middle of the room to the front. It is suspended on hooks above the mix position and stops floor-ceiling reflections building up and disrupts standing waves.

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