I had been using a warehouse/studio space with an artist and the acoustics were very bad. It was even hard to carry on a conversation across the room. The room was large, 25′ x 55′ x 13′. There were concrete ceilings and floors and insulated sheetrock walls. I had divided the space about in the middle with some 8′ high cabinets perpendicular to one wall and out 16′ leaving a 9′ walkway.
I started reading about acoustics in “The Master Handbook of Acoustics” and on Ethan Winer’s “RealTraps” site and the RPG site. Online can be found references to the Helmholtz resonator, QRD and skyline diffusers. RPG makes an absorber/diffuser based on binary numbers that looked like it would be tedious to build but not to difficult to achieve something similar.
I had a dozen pieces of 1/4″ HDF and material to build the frame so I laid out a 3/4″ grid on a 2′ x 4′ piece of the HDF. I marked the squares that matched the binary pattern I found online. Then I put that piece on top of a stack of six other 2′ x 4′ pieces and drilled a 1/2″ hole at the center of each marked 3/4″ square through all 7 pieces. These sheets were mounted onto a 5″ deep frame. I filled the frames with some bonded polyester fiber and others with open cell foam. These are all materials I had on hand, I just wanted to experiment to see how they would perform. I figured ifthe diffuser/absorbers worked at all with these materials they should work very well with rigid fiberglass or mineral wool.
Well, I made seven, hung them up and listened to some music. I had placed 2 on side at the first reflection point and 3 on the back wall opposite the speakers. It is difficult to describe what I heard. Definitely they made a positive difference but to correct a room like this one i would need much more. Unfortunately we left the space before I had time to take any measurements or do any more. They made enough of an impression though, that in my next listening room I am going to put in the time to get the acoustics as right as I can. That day is coming soon.