Wall treatment: bass traps, diffusers, etc.

[jeronimo]

The back wall where is the couch have 4.4m x 3.7m.
I'm thinking about puting bass traps in the corner w/ MDF boards of 1.2 x 2.4 w/ rock wool glued to the back and fixed into a "sealed box".
Leaving this traps from the floor up, will leave 1.3m of untreated wall 'till the ceiling.
What should I do? Put corner traps on the wall / ceiling corner? Hang drapes w/ rockwool?
What should be a good idea?
The wall area btw the corner bass traps will get a mid/absorber done w/ a perforated MDF board also w. 1" rockwool.
I'm thinking about making one of those wood blocks diffusers also.
Any ideas?

[knightfly]

If you don't have at least 3 meters distance between the back of your head and the rear wall, it's not generally recommended to use diffusion but to stay with absorption. Otherwise, there is a good chance your stereo imaging will suffer due to phase cancellations caused by early reflections... Steve

[spicyitaliano]

A quick question. (Hope you don't mind me buttin' in here )

My control room is 14 feet from front to back. The prime listening position (right behind console) is about 6 feet from the front wall. What should I use for the rear wall? Absorbtion or diffusion?

Thanks.

[knightfly]

If your room is 14 feet, your head is 6 feet from the front, that puts only about 7-1/2 to 8 feet between your head and the rear wall. This is the distance that matters. Sound travels at approximately 1130 feet per second, which means it will travel 1.13 feet per millisecond. Your brain tends to integrate any sounds that occur within about 20-25 milliseconds of an original sound with that sound, considering it all part of the same sound - if parts of the total sound envelope your ear gets are phase-delayed, such as would come from a speaker, bounce off the rear wall, and return to your ear, then there will be frequencies that are canceled out in varying degree depending on their wavelength.

If you keep that rear reflection path, which would be the time from when your ear first hears a sound until that sound reaches the rear wall and returns to your ears, if that path is longer than about 25 feet, then those reflected sounds will be at least 20 milliseconds later than the original sound. to do that, you need more than 10 feet from your head to the rear wall.

Even 10 feet is in the marginal range, so it's not really a good idea to use diffusion if you have less than maybe 12 to 15 feet behind you. Same thing with side walls - in a typical sized home studio control room, the side walls should be splayed - if they aren't splayed enough to reflect sounds to the rear of the room, they should also be absorbed... Steve

[dymaxian]

I don't know how much room you would have in the back if you did this, but it bears at least a mention...

With the layouts I've been designing and the basic 'manual' raytracing studies I've done, it seems to be pretty efficient to have the back wall angled to a point instead of concave, and having a valley. Reflections off the back wall (if there are any that arent absorbed) will head out toward the side walls instead of converging on your ears. It doesnt' have to be too sharp a point there, either... angling the walls 10deg against each other will probably be enough to make sure that there isn't a 1st reflection path from either speaker to the listening position. Obviously this depends on the overall room layout, but if you've got the room to do it this might help you out. If you have a hard back wall, you could probably angle the room treatment in this way.

Make any sense? The board's elders may correct me on this, if it creates more problems than it solves...

Good luck!

Kase
www.minemusic.net