Foam is pretty much useless. Actually it becomes counterproductive in that it muffles the high frequencies while doing absolutely nothing to anything below 200 Hz.

Broadband absorption is what you need, and that's provided only by a handful of materials (none of them "environmentally friendly", unfortunately...) There's a way to make super-effective corner traps on the cheap, and that's by buying Dow Corning 703 sheets (you don't need the thicker 705's because you're going to stack them anyway and 705's are considerably more expensive), cut them in large triangles and stack them one on top of another, floor to ceiling. Do that to every corner in your room. Then you can use extra 703 panels to treat early reflections and critical spots (a so called "cloud" --basically a 703 panel suspended 1 ft from the ceiling and placed right above your head-- is also of great help.) Don't forget to cover all the panels with non-porous fabric (yes, you need to surround the panels with wood frames and use a staple gun to seal the fabric) as fiberglass is not exactly healthy if it gets in your lungs...
If you think it's too much work and you don't feel confident enough to do it yourself, contact the guys at realtraps.com and they'll do it for you at reasonable prices.

Possibly everything in your room should be symmetrical, in order to preserve an accurate stereo image.

Damn, that won't be cheap. I'll see what i come up with.. I'll post my progress, but first a little vacation.
Thanks for al the advice you guy's :)

You bought $3,000 monitors and NOW you're cheaping out? :D

I believe they cost about 1450 euro a pair wich is not even $2000. But you're right indeed. The only problem I have is paying hundereds of euro for a few pieces of foam.

I calculated complete kit for about 650 euro on a dutch accoustics site. All I see is a foto of some foam pieces. I just don't understand why that as to be so expensive.

Rigid fiberglass is a lot cheaper than foam and a lot more effective. I don't know about Europe, but here in the US you can get a case of six 703 sheets for $74.

http://www.atsacoustics.com/item--Ow...f-6--1004.html

Just sent all the information to an accoustics expert. Lets see what he comes up with, really hope there is a solution..

But first a little vacation :)

More soon..

this is a very good thread with excellent points. bump.

There is a little irony seeing this topic popup today. I would have been building basstraps with a friend today, but since I had to see soccer (i'm from holland), I didn't go for it.
Another thing is that I wouldn't be building them for myself, cause there's just not enough room for basstraps in my tiny studio room wich doubles as CAD station.
If the traps work at my friends place, maybe I can find a way like hanging my speakers from the ceiling..
The commersial traps where a bit too expensive for me

www.acoustics101.com

This website is fantastic. I work with acousticians on studios and this is exactly what the big boys are doing. I'm working on one project out in NJ and the client is paying a fair amount for this same information (and a project mgr!). When I built my studio this page was my bible.

Also, you always want to reference as many systems as possible. Become familiar with your monitors. Listen to commercially done music that you know very very well and listen to how the bass sounds compared to the low mids compared to the mids to the highs. How are the dynamics? Familiarizing yourself with your monitors in the acoustic environment they're in is the most important thing you can do. You can have great monitors in a crap space and end up with a mix that doesn't translate very well at all.