Not to worry, my bad - sometimes I just get too much at once and don't want to short anyone. Still, not a total loss - here's what I got for you last night, things were slow enough to get some doodle-time -
Keith, I got a little time to work on your questions last night, and realized that there may be several changes that would work better for you - first, though, I need to know just how far along your construction is - how much of what’s on your drawing actually exists, and which parts are yet to be built?
Refresh my memory - what is the solid gray section inside your vocal booth?
For one thing, in your tracking rooms there is no need for everything to be symmetrical - if leaving out the angled construction on one side will leave you with more usable floor space, there’s no real reason not to do that. With your solid concrete outer walls, though, you WILL need lots of bass trapping of one kind or another.
You also still have (besides the ceiling and floor) another pair of parallel walls at the far ends of the live and dead tracking area.
I ran the modal response for your tracking area, attached is a plot of that. You will need to build absorbers for three different frequencies to tame the three pairs of modes that are too close in frequency to each other - These center frequencies are at 48, 149, and 298 hZ.
48 hZ is too low for practical Helmholz traps (slat resonators) without using excessive depth, so it would probably work better to build panel traps centered on 48 hZ, then tailor your slat resonators for 149 and 298 hZ. The 48 hZ panel traps should be placed at either or both ends of the tracking area, since that mode is a function of the width and length of the room the panel traps should be placed at all four corners of the room.
3/8” plywood over a 12” air cavity will give you the 48 hZ center frequency you need for the panel traps- these, being low frequency, should have all but the front panel built from heavy MDF - ¾” is fair, 1” is better. I would build four of these, 2 feet wide and at least 6 feet tall, sealing everything - you can use standard 6” house insulation inside, make sure the insulation doesn’t touch the front panel but is within 1-2” from it. You can “trap” the insulation by using chicken wire or other lightweight “hardware cloth” and a staple gun and fastening the wire mesh to the sides of the box all around. Thin wood lath or cleats over the wire with small screws where the wire lays flat against the side walls will make things stay put. This layer should hold the insulation at least 1” away from the inside of the front resonator panel of 3/8” plywood. All joints, including the front panel, should be caulked with acoustic sealant. All construction should be glue and screw. When finished, these traps can go in all four corners of your tracking area, facing each other, and against the walls. These are pressure activated traps so they need to be against the walls, not ¼ wavelength away.
At an average depth from the wall of 18”, a slat resonator with 1/10” slots between 5.5” x .75” slats, will have a center frequency of 146 hZ; with an actual depth of 12” to 24”, this would give a fairly broadband absorption centered at the 150 hZ frequency that needs treating. These should be the topmost section of your top orange section and the bottom-most section of your bottom brown section. I've numbered these #1 and #4 in my markup of your plan. For the dead end’s brown section, if slots make it too bright you can mount 1” 703 in front of (not touching) the slats with no ill effects.
Building this exact same slat resonator in front of an average cavity depth of 6”, but with the 5.5” x .75” slats spaced at 7/32”, will yield a center frequency of 300 hZ. That should be the other section of your upper orange and lower brown angles (sections 2 and 3), running from 0 to 12” deep. This 300 hZ mode coincidence, since it’s caused by the 4th harmonic of room height and the 6th harmonic of width, shouldn’t be nearly as strong as the others - however, that’s also the prime resonant frequency of typical kick drums, so having a trap centered on that frequency isn’t a bad idea even if it’s NOT one of the modal problems of the room.
For a good start on the basics of building these, click on the John Sayers Productions logo at the top right of this page, then click on “wall units” - You’d be building a modified version of the “Corner Unit”, or actually more like the “Wall unit” - actual spacing of the elements are spelled out in the two preceding paragraphs. These units also need to be sealed, except where the air goes through between the slats and through the cloth. They can be partially filled with any leftover insulation, either 703 or spun glass or rockwool. Try to keep the insulation spread out over the entire inside of the box, and fairly close to the front slats. If you have it, sheets of 703 will work well here.
As far as wall angles go, if you’re over 12 degrees total between two walls you’re fine. 1 foot in 10 gives about 6 degrees, so the 2 feet in 6 I drew for your traps will be plenty. The other two broadband absorbers (not 1, 2, 3, or 4) can stick out from the wall by 18-24” and be fine. This isn’t critical in the tracking area, symmetry is only required at the mix position.
Don’t use a car windshield - more problems than it’s worth.
2.5 pcf to 3 pcf rockwool or 703 should be used in all walls not otherwise specified, such as traps/absorbers.
I would only use MDF on free-standing units or for dividers between slat absorber sections - it’s too expensive for walls, and gypsum works as well for about half the price.
I would NOT carpet ANY part of the studio as a permanent thing - if it’s too live, you can always lay down an area rug. More choices that way.
On the vocal booth, I redrew part of it - with the new angles, you will probably want hard floor, 2-3” 703 ceiling, and 703 on at least one wall (probably opposite the slat absorber I added.) Don’t make it too dead, you can always do that later if it’s too live.
I think I covered just about everything you brought up so far - See what you think about the changes I made to your drawing… Steve
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