Earlier this year I had the priviledge of helping some clients convert part of their home into a home studio. This was no ordinary conversion either- we vaulted ceilings, added lots of mineral wool insulation, and then built enough acoustical treatments to make a room inside the room. It was a blast. (See these posts).
Anyway, they called me again today to build a couple more baffles to stick in the corners to help absorb more of the low end frequencies in the control room downstairs.
The majority of the baffles were made out of a wood frame around mineral wool insulation that is covered with acoustical fabric. These are hung from the ceiling to absorb reflections and hopefully help the engineer get an accurate impression of the recording.
To fight those pesky low frequencies, I took 4″ thick mineral wool insulation and built a small frame with some 1×2 that would go on the back. This would offer some support, but mainly I needed a place to staple the fabric. At this thickness, the insulation will basically stand on it’s own in the corner.
I put these in each corner behind the baffles I had previously made. I’m not an acoustic engineer, but my client tells me that the lower frequencies should get trapped in the airspace behind the new thick insulation and hopefully reduce the boomy low end and make it clearer.
Right. I just built the baffles and installed them. He says it sounds better. That works for me! 
-Peter
