Advice sought about mode problems in a small live space.

First of of all, thanks for a great site. I posed my quesion in Marshy land and some kind soul sent me in this direction. I have read the terms and conditions, so I'll try and give as much info as possible, but I can't do pictures at the moment. That said, I suspect that my problem is a common one and that the room's dimensions are the salient data. I hope that the solution is equally common. I'm an acoustic guitarist. I record for fun. The room in question is a detached garage built of wood. The basic structure consists of 2"x4" stud walls and a pitched truss roof. External cladding is clapboard. Internal panelling is 9mm hardwood ply on the four walls and the ceiling, and is untreated. The only insulation is thermal glassfibre in the walls and ceiling. The floor is concrete, covered with thin carpet and some heavy rugs. Overall internal dimensions are 5.95mx4.66mx2.32m. One long wall has 0.75m deep shelving, floor to ceiling, which is filled with 40 or so uniformly sized packing cartons. The other long wall has a 1mx1m closet at one end in the corner which houses the noisy computer. I have no pretensions about mixing in here; fortunately I have access to a friends 'proper' facility should I ever come up with anything worth bothering him with. In my explorations with mic placement on an acoustic guitar I have come up fairly and squarely against the room's modes. Well, to be precise, the vertical floor-ceiling mode. While I'm not concerned about mixing in here, I am concerned about recording. Having done some research both here and elsewhere I am basically familiar with the acoustical problems of small spaces, and I understand the difference between problems caused by the room's dimensional modes and those cause by reflections at any frequency. The latter I can live with, but the floor-ceiling mode is killing me. The most pronounced problem occurs, of course, with the note of A and its harmonics. I say "of course" because the floor-ceiling height is three times the wavelength of A-440. When I'm sat playing the guitar it's one A-440 wavelength off the floor, and one A-220 wavelength below the ceiling. No surprise then that when I play a note of A the guitar's top honks at A-220. I suppose that I could stand up and play! Trouble is, when I get to anything with a D note in it, I have the same problem, it's just down a fifth! So, I've got this problem with the room's floor-ceiling mode. My question is, "can I fix it, and if so, how?". Given the other problems associated with small rooms I'm already resigned to some broadband absortion on the walls. I realise that there are two other axial modes to consider, but if push comes to shove I can move the player around a bit and find a workable spot. The real bugbear is this vertical mode. Will broadband absorption be enough? Or should I also be considering some way of diffusing the vertically incident sound on the ceiling. I'm thinking perhaps of a cloud above the guitarist which would combine the two functions of broadband absorption and non-vertical reflection. I realise that with a 2.3m ceiling my problems are pronounced and the solutions will be limited. TIA. maccool.

> "can I fix it, and if so, how?" < Yes, and with bass traps. :) > Will broadband absorption be enough? < Sure. --Ethan

Ethan, thank you, that's encouraging! For the purpose of recording a solo guitarist, would it likely be sufficient to treat the ceiling above the guitar, and if so, with what, and covering what area?

Mac, > would it likely be sufficient to treat the ceiling above the guitar < That's a different issue. The best place to start with bass trapping is in the corners. But it's also useful to treat all nearby surfaces with absorption to avoid "early" reflections and comb filtering. There's a lot of advice about all of this in my Acoustics FAQ: www.ethanwiner.com/acoustics.html --Ethan