Here is my vocal booth. It was built over an infrequently used stairwell, hence the first couple of pics and some in the middle, whereas you can see the floor is flipped up. Most people won't have to construct such a thing.
Essentially, my vocal booth is about 5'x7'9", constructed of 2x4's packed with 409 rigid fiberglass on the inside, and ordinary encased house fiberglass on the outside. This occured because I was originally going to use ordinary insulation, stapled it to the outside of the framing from the console room, and a friend of mine acquired 703 after I put the plywood up, so instead of tearing it all out I just left it and put the 703 in from the inside. The 409 maintained its thickness moreso than the home insulation anyway, so I'm not worried about it being effective, or not. Should be fine.
The walls inside and out are layered with 3/4" thick commercial grade plywood, 1/2" sheetrock on top of that, and 1/4" sheetrock on top of that. The plywood itself is probably not terribly useful acoustically, but it did allow for drywall screws to be zipped in anywhere and everywhere. Each screw was dipped in an epoxy, then zipped into whatever material its supposed to hold up.
The plywood was also epoxied to the studs (and deck screwed, screws dipped in epoxy), both layers of sheet rock were glued to the plywood and each other, and those screws were dipped in epoxy as well.
Mudded, sanded, painted.
Is it a perfect vocal booth? Nope. Fits my needs and is solid as hell.
You will notice in some of the pictures, there is a double outside window on the wall next to the stairwell that I built the vocal booth over. I intended to remove those, until I discovered the windows themselves are supported underneath by a steel beam, and another steel beam overhead. So, I put the windows back in and said f*ck it.
The vocal booth wall goes right between the two windows, and is tied into the structure of the steel beams above and below, as well as the window frame itself. I've already cut the interior shutters for both windows, but haven't loaded the 703. The depth is there to do so. I haven't found a green fabric that matches my moulding yet, that's all that is holding it up.
Because the flip-floor has a large 4" gap between its edge at the top of the stairs and the entry door, sound clearly escapes and enters the vocal booth, from the console room its built within. However, I've done a lot of testing of this and found its not going to be a problem, for this reason.
I record all acoustical instruments, and vocalists, dry as a bone. So if I, in the console room, are wearing headphones, nothing bleeds back into the booth. The booth, as is, cuts down all the machine noise of my hard disk recorders which is really what I wanted. At some point I'll revisit that gap and make another flipping part that is spring loaded, so when the floor goes down, this thing flips over, and gasket that as well.
I've already done some experimental recordings in that booth (even though the room isn't done, I simply stacked equipment in piles in the console room and sat on the floor), and recorded a vocalist, and I've found that it's pretty good overall. I had purchased some foam for the wall that the entry door is in, and planned to install a 3' wide x 7'8" high (ceiling height) 703 framed panel in the corner which the vocalist will be facing, but I may not have to do that. I have more recording and experimentation to do.
The window facing the console room (the white framed window) is an ordinary dual pane window (safetyglass) filled with argon, to which a carpenter friend of mine constructed another frame that fits inside the recessed window (its recessed on the booth side, flush with the console side), which will enable me to hang an angled, 1/4" thick piece of safety glass, to further isolate noise from the console room and the vocal booth. Its been constructed and painted, gaskets installed, all I have to do is mount the hinges on the bottom and the two latches on the top. Test fitting was successful. When its latched, the gaskets seal very nicely. I used generic automotive door gaskets from JC Whitney, they are rubber and easily worked around the perimeter of the window. They get compressed to about 1/2 their thickness, which is more than is done in automotive applications, and it seals very well. I put a battery operated doorbell between the angled, gasketed window and the existing window, held the angled window in its position so the gaskets were compressed, and my cousin pushed the doorbell. I could barely hear it on either side. Good test? Naaah. Was fun though
