Plan for iso booth in basement with odd floor

Phase 1: Build wall on west side of monitoring position (in red) and iso booth (purple). General info: -House is built into a hill- east wall of basement is underground, west wall opens into back yard. -Aren't really any external constraints. Quiet neighborhood and neighbors are far enough away. -"Control room"/ monitoring position to remain open for whole N/S width of room -Budget ~$1,000 for materials (could be more if needed) Isobooth- Goal- to be able to track acoustic instruments/vocals on sensitive mics while also recording drums/horns in main room. Don't play very loud music (mostly jazz & RnB)- a little bleed is no problem. Plan- Using Mr. Sayers iso booth design from this forum, I'd like to build a free standing room (in purple) within the larger room. And short wall (in red) on west side of monitoring position. Ok, so here's the weird thing about this room: The east end of the room (where the control area would be) is flat like a normal basement- but just west of the wall I want to add (in red) the whole floor starts sloping down. The ceiling of the area with the flat floor is too low to build beneath rafters (6'11"), so isobooth needs to be further west. If I can put it approximately where it is in the picture I can still maintain decent line of site with rest of studio. Height to eastern most (lowest) rafter at this position (middle of room) is 7'7" Questions: 1. Balance on monitoring position: will having the east wall underground and west wall (to be added- in red) with a room on the other side throw off the stereo balance? 2. Is it going to compromise the design of the booth to shorten its external height about 7 inches? Or would I need to go even further west? Assuming that's feasible, the next issue would be what to make the floor of the booth out of, since it would need to 'float' in order to be level. I have some ideas here, but thought I'd check these other questions first. Thanks very much. edit- to clarify, it's 6'11" and 7'7" from floor to bottom of rafters.

Hi "Bass", and welcome! :)

The east end of the room (where the control area would be) is flat like a normal basement- but just west of the wall I want to add (in red) the whole floor starts sloping down.

There's a reason for that slope: the architect must have expected water there, and that's his way of getting rid of it. I'm guessing there is some kind of sump or drain at the bottom of the slope?

1. Balance on monitoring position: will having the east wall underground and west wall (to be added- in red) with a room on the other side throw off the stereo balance?

That should be fine. As long as the new wall is fairly massive and doesn't act as a panel trap, there shouldn't be any effect on the symmetry.

2. Is it going to compromise the design of the booth to shorten its external height about 7 inches?

Sound waves like space. Things sound better if you have bigger, taller rooms, so reducing the height by 7 inches means it won't be as good as it could have been, but that doesn't mean that it will be bad. And there's one overriding concept for most studio builders: If the choice is to have a not optimal studio or no studio at all, then "not optimal" wins out, any day! :) Suitable treatment can help a bit.

Assuming that's feasible, the next issue would be what to make the floor of the booth out of, since it would need to 'float' in order to be level.

To lose the least amount of height, I would just pour in some self-leveling cement. Trying to float a floor is no easy task, especially such a small one: it will be very hard to get enough mass on it to actually make it float. Also, have you considered trying to interleave your new ceiling joists for the booth between the existing joists above you, on the subfloor? You can save several inches like that. Another alternative is to build the ceiling "inside-out", with the joists underneath and the drywall on top. That way, you can leave just a very small gap between the drywall and the subfloor joists. - Stuart -

Hi Stuart! Thanks, and thanks a ton for your responses.

Soundman2020 wrote:

There's a reason for that slope: the architect must have expected water there, and that's his way of getting rid of it. I'm guessing there is some kind of sump or drain at the bottom of the slope?

Oh man, at LAST somebody comes up with a credible explanation for that floor. Everyone else has been like "I've never seen anything like that." There is a drain, though it's more towards the middle, and the floor keeps sloping down from there.... Atanyrate, a small amount of water did used to come in if there was a torrential downpour, but dealing with the eves has solved that.

Soundman2020 wrote:

That should be fine. As long as the new wall is fairly massive and doesn't act as a panel trap, there shouldn't be any effect on the symmetry.

Does "fairly massive" mean more than two sheets of dry wall, 703 and 2X4's? Should I look at using brick or something?

Soundman2020 wrote:

Sound waves like space. Things sound better if you have bigger, taller rooms, so reducing the height by 7 inches means it won't be as good as it could have been, but that doesn't mean that it will be bad. And there's one overriding concept for most studio builders: If the choice is to have a not optimal studio or no studio at all, then "not optimal" wins out, any day! :) Suitable treatment can help a bit.

Right, and this is defintly one of those "not optimal" sort of situations! :lol: My main concern was if that would effect the dimensions in a way that should compensated for somewhere else in the design? Like it would create nodes or something? (Can you tell what an expert at acoustics I am? :P )

Soundman2020 wrote:

To lose the least amount of height, I would just pour in some self-leveling cement. Trying to float a floor is no easy task, especially such a small one: it will be very hard to get enough mass on it to actually make it float.

That sounds like a great idea.

Soundman2020 wrote:

Also, have you considered trying to interleave your new ceiling joists for the booth between the existing joists above you, on the subfloor? You can save several inches like that. Another alternative is to build the ceiling "inside-out", with the joists underneath and the drywall on top. That way, you can leave just a very small gap between the drywall and the subfloor joists

Oh yeaaaah, if I'm understanding you there, that would make perfect sense- The booth joists would just connect between the existing joists, then the ceiling would hang from those? Am I following you here? Thanks again for your input.

Does "fairly massive" mean more than two sheets of dry wall, 703 and 2X4's?

If you mean two sheets of fire-rated 5/8" drywall, then yes, that would be fine. But if you want isolation from the rest of the basement, then that would only be your inner-leaf, and you'd need something similar for the outer leaf: another set of studs, also with 2 x 5/8" drywall.

Should I look at using brick or something?

You could, but it isn't really necessary. Drywall does a pretty good job of isolating for the vast majority of studios.

My main concern was if that would effect the dimensions in a way that should compensated for somewhere else in the design? Like it would create nodes or something?

I think you mean "modes" not "nodes". :) But modes are a fact of life, regardless of the room size. Modes exist simply due to the dimensions of the room, and making the ceiling lower does not "create" or "delete" modes: It just means that the modes will be at a different frequency, which might or might not be good...

certainly wouldn't be opposed to that, but that would probably require a go ahead from a structural engineer? Not quite sure that would be in the budget...

Well, it is always good to get a structural engineer involved in a studio build, due toe large amounts of mass that will be hanging over your head, but it makes no difference from the point of view of where the new joists go: They have to be dimensioned correctly to carry the load of the ceiling, regardless of whether they go above the drywall, or below it, or whether or not they are interleaved between existing joists if they go above the drywall. The load is still the same.

The "inside-out" option sounds like it might be more feasible in this space. Would that mean just using twice the drywall on the top and leaving the frame "open" on the inside with 703 between the booth joists?

You don't need double the drywall: still the same amount. The only difference is that it goes on top of the joists, not below them. The amount of mass does not change. OK, caveat on that: It MIGHT change in the specific case that putting the drywall on top would then bring your inner leaf too close to the outer leaf, such that the MSM resonant frequency rose too high to be useful for your isolation goals. But that is rather unlikely with typical basement ceiling joists, and especially considering this is just a vocal booth. If it were a drum booth, or if it were under smaller 2x4 ceiling joists, then that might be different, but you are probably OK. - Stuart -

Soundman2020 wrote:

If you mean two sheets of fire-rated 5/8" drywall, then yes, that would be fine. But if you want isolation from the rest of the basement, then that would only be your inner-leaf, and you'd need something similar for the outer leaf: another set of studs, also with 2 x 5/8" drywall.

Yes, that's exactly what I had in mind. Single leaf for now, but doing it right so if I wanted to add a second one later it would work. Should I plan on using Green Glue between the two sheets of drywall then?

Soundman2020 wrote:

I think you mean "modes" not "nodes". :) But modes are a fact of life, regardless of the room size. Modes exist simply due to the dimensions of the room, and making the ceiling lower does not "create" or "delete" modes: It just means that the modes will be at a different frequency, which might or might not be good...

(facepalm) Yes, modes, haha. I guess what I'm wondering if there's anything I could/should try to work out in that regard while still in the planning stage?

Soundman2020 wrote:

You don't need double the drywall: still the same amount. The only difference is that it goes on top of the joists, not below them. The amount of mass does not change. OK, caveat on that: It MIGHT change in the specific case that putting the drywall on top would then bring your inner leaf too close to the outer leaf, such that the MSM resonant frequency rose too high to be useful for your isolation goals. But that is rather unlikely with typical basement ceiling joists, and especially considering this is just a vocal booth. If it were a drum booth, or if it were under smaller 2x4 ceiling joists, then that might be different, but you are probably OK.

I think I phrased that poorly- what I meant was, would the total amount of drywall that would've gone on both sides all need to be put on the outer layer then? So 3 sheets all together? I'm guessing that's what you mean when you say "The amount of mass does not change"? Upon further consideration, I'm starting to think the best route might be interleaving with the existing joists, then once I can actually get in the booth figure out if there's enough height for 6" of 703. Thanks again for your help.

Should I plan on using Green Glue between the two sheets of drywall then?If it fits your budget, and if you need good low frequency isolation, then sure! That's a good idea.

I guess what I'm wondering if there's anything I could/should try to work out in that regard while still in the planning stage?

Use a room mode calculator (sometimes called "room ratio calculator") to check that. Find a good ratio close to the dimensions of your room, and see how you can adjust the dimensions to get even closer. But you don't need to go crazy: Just stay away from the bad ratios, and get close to one of the many good ratios, and you'll be fine.

I think I phrased that poorly- what I meant was, would the total amount of drywall that would've gone on both sides all need to be put on the outer layer then? So 3 sheets all together?

Exactly. That's it!

Upon further consideration, I'm starting to think the best route might be interleaving with the existing joists, then once I can actually get in the booth figure out if there's enough height for 6" of 703.

That's what I would do! And if you build inside-out, then the joists are inside the booth, so you have enough room for at least 3 1/2" of insulation, which should probably be enough. - Stuart -

Hello again- I had to put this project on the back burner for a while (has it been a year already??), but I think I'm going to be ready to move forward this spring, so I'm back with some more questions… 1. In the interests of keeping things as simple as possible, I was wondering about alternatives for power and audio i/o other than running them through the walls (or having lights in the ceiling). Since I'm going to pour concrete for the floor, is it a silly idea to just run cabling through that? Something like two smallish PVC pipes that I can put cables through and then seal the ends of? 2. For the air circulation… I've got the picture with the vent diffuser, I'm assuming those will need some sort of "active" ventilation? What are typical options for fans? Thanks!

1. In the interests of keeping things as simple as possible, I was wondering about alternatives for power and audio i/o other than running them through the walls (or having lights in the ceiling). Since I'm going to pour concrete for the floor, is it a silly idea to just run cabling through that? Something like two smallish PVC pipes that I can put cables through and then seal the ends of?

That's actually a great idea, if done correctly. Make the conduit a decent size, in case you need to add extras later. Or just add an extra empty conduit, for the same reason.

2. For the air circulation… I've got the picture with the vent diffuser, I'm assuming those will need some sort of "active" ventilation? What are typical options for fans?

That's a whole different subject, that needs many pages! A couple of books, in fact... :) Search the forum for "HVAC" and you'll come up with hundreds of links to threads that mention the subject of how to do ventilation and air conditioning for your studio. It's a lot mote complex than most people think... - Stuart -

Soundman2020 wrote:

That's actually a great idea, if done correctly. Make the conduit a decent size, in case you need to add extras later. Or just add an extra empty conduit, for the same reason.

I'm thinking I'll put two in and use one for audio lines and the other for electrical. Probably just PVC, or should I use something heavier? I was thinking I'd run the cables through, then fill the rest of the conduit up with sand and cap the ends with some of that pipe insulation used for water lines. That way I've got plenty of mass in there, but could potentially switch out a cable in the future if needed. Does that sound reasonable? Thanks

I wouldn't fill them with sand. Just push some fiberglass insulation down each end, and cap it liberally with acoustic caulk. That way you can pry off the caulk and pick out the insulation if you ever need to pull more cables. You'd never be able to get the sand out, if you filled them with sand. Use ordinary electrical conduit. - Stuart -

That makes sense. I was thinking I could just vacuum it out if I needed to run different cables, but as usual your way makes a lot more sense. :lol: Thanks again