Here’s how I built a pair of simple broadband absorbers to cut down the room sound in my studio. These work as good as specialized acoustic treatments, but cost far less, and their absorption is good down to the 500Hz region, and it’s fairly flat across the spectrum. Note that absorbers don’t stop outside sounds from getting into the studio… they do shorten the reverb time of instruments as they are played in the room.
It’s really nothing more than a simple wooden frame with fiberglass fill, covered with cloth. Mine measured about 5’6″ by 30″. I used cheap 1×3 lumber (which is really about 5/8″ x 2 1/2″), but a true 1×4 would be better. If you use cheap wood, count on spending more time building them… I had to pre-drill all the nail holes to prevent the weak wood from splitting. I also used construction adhesive on all the joints.
Once the frame is built and the fiberglass positioned, all you have to do is attach the cloth. I used a staple gun. They are fairly light, so they can hang on the wall with a simple screw. There may be times when I’ll want more room sound… then it’s a simple matter to move these somewhere else. Or stack them around a guitar amp, for example… they’re very handy to have around.