I've been directed here by you from the music player forum, where I was looking for info on "bass trap pit". I do not know if it is called like that, I only recall reading about something like that many years ago. It was a pit or trench in the floor in front of the back and/or front studio wall, and this cavity would be filled with sound absorbing material.
That's a neat idea! If your floor is easy to dig out, I would imagine that would work great. Only problem is if you fell in : ( Other than than that and taking up otherwise useable floor space it's great. I suppose, a grate could be installed over the pit or you could build something of wood but with narrow enough slots that you could not trip on or get your foot stuck in. (no stiletto heels!)
Acoustically, follow the same "formula" as other porous absorbers: Deeper (thicker )= lower effective frequency. More area coverage=more percentage of overall absorption. Kraft paper or thin plastic membrane over the front surface increases low frequency effectiveness at the expense of mid and high freq absorption.
Hi Rock, I suppose that there has to be a metal grid placed over the opening, indeed. And...stiletto heels would only be a distraction in the studio anyway, so I'd rather receive those somewhere else, LOL.
I imagine that such idea would be an integral part of the design and construction of the studio. Should it really be of added value acoustically, then one could think of doing it in the ceiling instead, or both, or what about in all the other corners of the room?
That is why I'm interested in finding reading material on this topic; the theory behind it, how the waves would behave, reflect/deflect differently than in a normal corner, etc.
I really don't think there is anything different about it. To me, it's a porous absorber like the ones mounted on the wall, it's just recessed in the wall, ceiling or floor. The one thing that is different though is the boundary of the room is now behind the pit so if the room appears rectangular, the actual shape of the room will follow into the solid wall behind the "pit' absorbers. I don't think that's going to be a problem but it will mix up the modal response and if you measure, you may see some other peaks and nulls but the absorbers will do more good than the modes do bad, especially if the absorbers are deep.
Back in the '80s when I did not understand this stuff as much as I feel I do now, I built a control room with obvious bass problems. One thing I did to try to fix it was to remove the drywall over the console (about 4 x 6 feet, there was about 2 feet of insulation we had installed above the control room ceiling and the ceiling of the existing building) and covered the hole with grille cloth. It seemed to help.
Thanks prodba for moving this here, and thanks Rock (as always) for chiming in. I agree that it's a nice idea to build trapping into the floor (or walls or ceiling), and it's also a good idea to have a metal grate over the opening! Carpet over the grate will hide it, and still let bass pass through.