Vocal Booth (Closet) Foam Out

Greetings, I am converting a closet in my apartment into a vocal booth for recording voice overs and am not sure how to flatten the sound. I've been told to start foaming it up and stop when it sounds good. My problem is that I don't have a bunch of expensive foam laying around -- I have to order it and have it shipped, so I don't want to do that too many times, and put up foam in the wrong places and have to tear it down and put it back up, etc. Specifics: 5' long, 2' wide 8' high opposing walls are parallel hard plaster/lath walls and ceiling hardwood floor 24"x80" hardwood door (single-panel, very thin) There is a 1' deep shelf which is 6' off the floor that I would like to keep if at all possible. The closet extends beyond the door 2' to the left and 1' to the right, so I would place the mic on the left side. One short wall (on the right of the attached drawing) has a brick exterior and the other three walls are interior. At a minimum, I'm planning on putting 6"x6"x6" cubes in the four ceiling corners, 6"x6"x24" bass traps between them and from ceiling to floor. I've read that at least 2" thick foam should cover the four wall from the ceiling down no less than five feet, that one wall should be completely foamed, and that the ceiling should have no less than 4" of foam (one person suggested 12" thick!). I figure with such a small room I should just go ahead and completely foam all four walls. Beyond that, I'm not sure what to do, particularly with the door. I know I can't sound proof it, but I thought covering both sides of it with foam extending beyond the outline of the door would help. Any suggestions would be greatly appreciated. Thanks!

Aloha and welcome to the forum, JP :D

I've been told to start foaming it up and stop when it sounds good.

Most of the treatments prescribed here on the forum have called for either Owens Corning 703 or Roxul (or equivalant) AFB mineral wool @ 2"-3" thick and a density of 2.5 pcf rather than the average "foam" treatments. I believe a search on "acoustic foam" would confirm this. Here's an excerpt of a thread on vocal booth acoustic treatments - be sure to note the bold points. My understanding of small vocal booth/voice-over treatments tend to lean toward the "dead" side. During the insulating phase of my front soffits, I noticed how nice and quiet it got with each 4' x 2' x 3" section of rockwool that was installed. Bryan Giles cautioned however, against building a square booth saying; "Be careful, a dead square booth will have low end issues (you'll hear the issues on your mic.) Steve (Knightfly) mentioned that "4' x 5' x 7' inside dim's is about the best modal compromise for a small booth." Modally, with a 6'4" ceiling you'd do well with wall dimensions (inside) of 5 and 7 feet. That combination shows no modal problems at all. This means that vocals in such a room shouldn't be "colored" by the room. You would want to keep the upper half, including the ceiling, absorbed with such as rigid fiberglas insulation boards, covered with a light plastic film (they shed) and fire proofed cloth (they're ugly) - you'd likely get better vocal sounds with the singer seated rather than standing, since otherwise they will be nearly at the ceiling. Being that close to a boundary (especially if it isn't absorbed) will cause comb filtering due to early reflections. Mode-wise, a 5 x 6 x 7 (inside) booth looks very good. It will also fit into an 8 foot ceiling area if necessary, and is big enough for 3 (very) friendly vocalists or 1-2 with a guitar, so that's what I'm going to start with. Once I finish (don't stop breathing while you wait, I have 'way too many projects still open) you could change dimensions to suit, just do NOT make any two dimensions the same, or more than one dimension in even # of feet.

Beyond that, I'm not sure what to do, particularly with the door.

You could hang a slab of OC 703/AFB mineral wool on the inside of door as well. :wink:

There is a 1' deep shelf which is 6' off the floor that I would like to keep if at all possible.

Is it possible to raise it up a foot to the 7' mark? (see Steve's comment) Hope this helps, Aloha 8)

Aloha and welcome to the forum, JP :D

I've been told to start foaming it up and stop when it sounds good.

Most of the treatments prescribed here on the forum have called for either Owens Corning 703 or Roxul (or equivalant) AFB mineral wool @ 2"-3" thick and a density of 2.5 pcf rather than the average "foam" treatments. I believe a search on "acoustic foam" would confirm this. Here's an excerpt of a thread on vocal booth acoustic treatments - be sure to note the bold points. My understanding of small vocal booth/voice-over treatments tend to lean toward the "dead" side. During the insulating phase of my front soffits, I noticed how nice and quiet it got with each 4' x 2' x 3" section of rockwool that was installed. Bryan Giles cautioned however, against building a square booth saying; "Be careful, a dead square booth will have low end issues (you'll hear the issues on your mic.) Steve (Knightfly) mentioned that "4' x 5' x 7' inside dim's is about the best modal compromise for a small booth." Modally, with a 6'4" ceiling you'd do well with wall dimensions (inside) of 5 and 7 feet. That combination shows no modal problems at all. This means that vocals in such a room shouldn't be "colored" by the room. You would want to keep the upper half, including the ceiling, absorbed with such as rigid fiberglas insulation boards, covered with a light plastic film (they shed) and fire proofed cloth (they're ugly) - you'd likely get better vocal sounds with the singer seated rather than standing, since otherwise they will be nearly at the ceiling. Being that close to a boundary (especially if it isn't absorbed) will cause comb filtering due to early reflections. Mode-wise, a 5 x 6 x 7 (inside) booth looks very good. It will also fit into an 8 foot ceiling area if necessary, and is big enough for 3 (very) friendly vocalists or 1-2 with a guitar, so that's what I'm going to start with. Once I finish (don't stop breathing while you wait, I have 'way too many projects still open) you could change dimensions to suit, just do NOT make any two dimensions the same, or more than one dimension in even # of feet.

Beyond that, I'm not sure what to do, particularly with the door.

You could hang a slab of OC 703/AFB mineral wool on the inside of door as well. :wink:

There is a 1' deep shelf which is 6' off the floor that I would like to keep if at all possible.

Is it possible to raise it up a foot to the 7' mark? (see Steve's comment) You may also want to move the mic position away from the ends/corners as in your diagram. Hope this helps, Aloha 8)