Treating a Whisper Room for recording

I have a 4' x 6' x 6'11" (interior: 3'10" x 5'10" x 6'8") Whisper Room MDL 4872S. It came with six 2' x 4' x 2" Auralex pyramid foam panels. I installed two each on the longer walls, one on the back wall, and have attempted to attach one to the ceiling, but even industrial strength Velcro doesn't have strong enough adhesive. I should get some Super 77 or something. The most noticeable problem is boominess. I record vocals and acoustic guitar in the booth, and the bass response sounds inconsistent and too much at times. I've read that's a common problem with small rooms, and bass traps in the four vertical corners are generally the best starter solution. But which bass traps? I've read that the OC 703 style ones need to have a sizable air gap to really reach the low end. The room's already tiny, so I don't want to make it more claustrophobic. I considered throwing 1'-wide 3/4" plywood or MDF (having a hard time finding NRC ratings on these materials) in each corner to get rid of the right angles. A cheap and easy attempt, however less than ideal. I suck at building things (hence the prefab booth), and commercial solutions appear to break $500, which seems a bit much. What to do?

Another thought is measuring the room with REW to get a more precise idea of what's wrong with the room. Since I don't want to commit to anything yet, I'd be using my AT4050. I'm thinking that should be fine, even though it's colored, because it's the only mic I have and use. And it's relatively flat. Good enough.

The most noticeable problem is boominess.

Right. There really isn't much you can do about that, either. That's the problem with small rooms: you are up against the laws of physics. In order to fix it, you do need deep absorption, but the amount of absorption you need won't fit in the room: there would be no space left for you in there. And even if it could fit, the room would sound so dead and life-less as to be very uncomfortable, and probably unusable. That's not to say that you can't do something, and at least improve it! You sure can. But it is never going to sound fantastic, simply because of the size.

I record vocals and acoustic guitar in the booth

You could probably make it reasonably good for vocals, but I don't hold out a lot of hope for the acoustic guitar.

I've read that's a common problem with small rooms, and bass traps in the four vertical corners are generally the best starter solution.

There isn't enough room in there for the type of corner trap that works well. The recommended size is 36" across the diagonal, making them over 2 feet deep along the edges. Obviously, you can't even fit such a trap into your room.

I've read that the OC 703 style ones need to have a sizable air gap to really reach the low end.

OC-703 is excellent, and probably your best bet. However, it is a myth that you need it to be extremely thick with a very large air gap: That only applies to normally incident sound (sound waves that hit the panel exactly head on), but for sound waves that hit at any other angle, then automatically "see" a much greater depth of absorption in front of them. The higher the angle of incidence, the greater the depth. So in reality, for randomly incident sound, absorption does still happen at much lower frequencies than are predicted by the equations for normally incident sound alone, and even with relatively thin absorption and a relative thin air gap behind it, you still get reasonable absorption down to useful frequencies.

I considered throwing 1'-wide 3/4" plywood or MDF (having a hard time finding NRC ratings on these materials) in each corner to get rid of the right angles.

That would do nothing useful. The sound waves you are dealing with in the modal range for your room, have wavelengths in the range 4 feet to 14 feet, so they won't even notice an object that is only one foot wide. So that would not help at all to reflect those waves. Even worse, you don't even want to be reflecting them in the first place! You want to be either absorbing them or diffusing them. There isn't enough space in there to build diffusers large enough, so your only option is absorption.

What to do?

I would start by just getting a couple of panels of 4" thick OC-703, and putting them on adjacent walls. It doesn't really matter which two adjacent walls, but it would probably be easier to put one on the wall opposite the door, and two on one of the side walls. Also put one on the ceiling. If you have any left over, then put a double thickness right in the corner, or better still angle a piece diagonally across that corner, if you can afford the space to do that. That's about all you can do at low cost. As I mentioned, it's not going to make your booth sound like Abbey Road! But it will help a bit to take the edge off the boominess. However, it will also sound pretty dead in there, since you are over-treating it, but there's not other real solution. If you find that the high end of the spectrum is disgustingly dead, you could try wrapping some or all of the panels loosely with plastic. Use reasonably thick plastic, not the thin stuff that garbage bags are made of. Experiment with different thicknesses and different amounts of coverage, to see if you get a useful benefit from that. And please do let us know how it goes! - Stuart -

Thank you for the suggestions. I'm okay with a dead room. I knew it wasn't going to sound good when I bought it. Figured I'd throw some reverb on the signal so it sounded like I'm in another, better room, which is what I've been doing with varying results. The louder I am, the more the room sound becomes noticeable, and more the reverb carries that not-so-good sound. The acoustic guitar sound is really not bad, even with my current treatment. Just some notes here and there than boom more than others. I mostly fingerpick rather quietly, so maybe the close miking is helping with that. I've been fixing the boomy notes using dynamic EQ, but of course that's a cheap fix and doesn't solve the problem at the source. Would something like LENRD bass traps help? Or would the change be so subtle that I couldn't possibly justify the $510 (I think that's right) it would cost to stack them floor to ceiling in the four corners?

Honestly, one of my aversions to DIY is that I'm afraid it will look terrible when I'm done, judging by past attempts at other projects. The professional look inside the booth has an inspirational quality. I guess that comes at a cost. Many commercial treatments look good. Really good. Maybe part of me is hoping someone will convince me to set aside a larger budget so I can justify paying for aesthetics in addition to function.

You can buy ready-made panels from places like Real Traps and GIK Acoustics. Their respective owners are both forum members, and they both make fine products that work. Contact them for quotes. They aren't the only ones that make such panels, by any means, but they are both very helpful. respected forum members, and they do make good stuff. http://www.gikacoustics.com/ http://realtraps.com/ I'd suggest you contact them. - Stuart -

I'm rethinking this from the ground up and will probably make another post. I appreciate your input very much. It got me thinking about the possibilities and about my budget for the project.