Vocal Booth Floor and Ceiling Design

[Kebberj]

Hi Everyone. This is my first post on this forum. I’ve been going through a lot of old posts and found a lot of extremely useful information - it’s a fantastic resource. I’ve found a lot of answers to my questions already, however, I was hoping to get some more specific help with my particular project as there’re a few key things that I can’t seem to figure out fully.

Purpose of this post:

I need some help with the floor and ceiling design of a DIY vocal booth.

Here’s some background info:

I live in Japan and work for a booking agency that hires out singers for studio recordings. We regularly have new recruits and I need to record rough singing demos that I can present to my clients. They don’t need to be pristine quality.

We recently moved our office to a rented apartment on the 4th floor of a condominium. There are three adjacent rooms and the center room, the kitchen/dining room, is empty and not used. This is where I’d like to build a vocal booth.

The building itself is concrete, however, the internal structures are wood-framed with plywood walls and no insulation (as far as I can tell). We only have neighbors to one side and directly below. The room itself is pretty quiet - I measured the following data using the RTA Pro and Decibel meter app on my phone:

(averaged over several measurements, A-weighted)

dB Average: 36.4 dB
dB Peak: 45.3 dB

125Hz: 24 dB
100Hz: 27 dB
80Hz: 27.8 dB
63Hz: 26.6 dB
50Hz: 31.5 dB
40Hz: 32.3 dB

Although the room is quiet, sometimes I can hear the neighbors very easily, such as when they use a vacuum cleaner or shut the front door hard. This is no problem for us, However I want to minimize noise issues for them, i.e. singing in a booth.

Here are the pictures of the booth space, flooring and floor plan:

Booth space.jpg

Booth room floor.jpg

floor plan.jpg

Here’s the basic overview of my plan so far:

Booth dimensions: 175cm (length) x 135 cm (width) x 217 cm (height)
Usage: vocals demos only (various styles of music)
Budget: US $2000
HVAC system: yes - DIY plan
Window: none

Weight (approx.): 9mm plywood @ 5.05kg/m2 x 23m2 = 116kg
4x2 pine @1.8kg/m2 x 66m = 120kg
fluffy wall insulation @ 1kg/m2 (10cm thickness) x 21m2 = 21kg
inside acoustic fiberglass insulation @ 2kg/m2 (5cm thickness) x 8m2 = 16kg
total approx. weight: 273kg (plus fabric, caulking, HVAC & door rubber etc)

I have been told by the landlord to keep the weight of the booth under 180kg/square meter, in accordance with the local building code requirements. The dimensions of my booth are 175cm (length) x 135 cm (width) x 217 cm (height), so the exterior floor space would be 2.36 square meters, which will allow the booth to weigh 425kg minus the occupant, so I guess I’d have to keep the total weight under around 340kg to be safe.

That’s not a lot of mass to work with, and I know that mass is all-important, however, I don’t need studio-quality isolation. I just need enough attenuation to keep the neighbors happy. I figure if I can get 25 - 30db of attenuation, that would be enough.

My idea is to build a 2x4 framed booth with fiberglass insulation (walls, ceiling and floor), and use 9mm plywood for the inner and outer leaves. Obviously plasterboard would be a better choice for the sake of mass but I’ll have potential weight issues if I do.

Here's a cardboard model of what I’ve designed so far (to scale!). I took the front wall and ceiling off as well as the inner panels so you can see everything.

Booth model.jpg

So here’s where I need some advice:

1. My main concern is sound transmission through the floor below - How can I minimize this? I’ve read on other posts that sitting a booth on a 2” sheet of OC 705 will help minimize transmission. Is that the best option for me?

2. Is a 2x4 framed floor (filled with fluffy insulation) a good idea, or would it be better just to go with thick, layered plywood? Or something else? Or am I doomed because I’ve got wood frames on a wood floor??

3. The ceiling height of the room is quite low (222cm) and if I allow for an internal booth height of 195cm (before treatment), I only have 27cm left for the floor and ceiling thickness. Minus the top and bottom frames (89mm x 2 + 9mm x 4), I’m left only with 5cm, which is tight in the room and not really a great internal booth height. So, instead of using frames for the ceiling and floor, I was wondering if I might be better off using two sheets of plywood sandwiched around a sheet of mass-loaded vinyl. I would reclaim a large amount of headroom if I could do that. But would that hinder the isolation performance of the booth dramatically? Again my booth doesn’t need to be incredibly isolated.

4. Is there a minimum gap I should leave between walls and ceiling?

Thanks in advance for your help. Any help would be intensely appreciated!!!

[Gregwor]

The room itself is pretty quiet - I measured the following data using the RTA Pro and Decibel meter app on my phone:

(averaged over several measurements, A-weighted)

You should buy an actual real SPL meter, measure with C weighted and slow setting.

Booth dimensions: 175cm (length) x 135 cm (width) x 217 cm (height)

Make this as big as you can and see that your dimensions don't fail Bob Golds Room Mode Calculator tests.

9mm plywood @ 5.05kg/m2 x 23m2 = 116kg

Use mass law equation to figure out how much isolation this will give you.

Use Green Glue Compound between your sheathing.

Build your room inside out so that you maximize your internal volume and you start with a dead sounding room (all of your walls will be lined with insulation due to the inside out construction)

Here's a cardboard model of what I’ve designed so far (to scale!). I took the front wall and ceiling off as well as the inner panels so you can see everything.

Wow. That takes skill.

1. My main concern is sound transmission through the floor below - How can I minimize this? I’ve read on other posts that sitting a booth on a 2” sheet of OC 705 will help minimize transmission. Is that the best option for me?

2. Is a 2x4 framed floor (filled with fluffy insulation) a good idea, or would it be better just to go with thick, layered plywood? Or something else? Or am I doomed because I’ve got wood frames on a wood floor??

I would build the floor out of thick wood with a 2x4 frame around it all sitting on thick 703 or 705. I believe that will be your best chance of decoupling your booth from the floor.

3. The ceiling height of the room is quite low (222cm) and if I allow for an internal booth height of 195cm (before treatment), I only have 27cm left for the floor and ceiling thickness. Minus the top and bottom frames (89mm x 2 + 9mm x 4), I’m left only with 5cm, which is tight in the room and not really a great internal booth height. So, instead of using frames for the ceiling and floor, I was wondering if I might be better off using two sheets of plywood sandwiched around a sheet of mass-loaded vinyl. I would reclaim a large amount of headroom if I could do that. But would that hinder the isolation performance of the booth dramatically? Again my booth doesn’t need to be incredibly isolated.

Build your walls and ceiling out of the same material (surface density I mean). There's no point in beefing up one more than the other. Also, make sure your door matches the same surface density and I'd recommend 2 sets of seals (bank vault style). Also, don't use a through hole handle. Use an automatic door closer to close the door.
The floor should have more surface density than the walls due to it needing to be sturdy as hell as it's only sitting on insulation.

Also, you will need ventilation silencer boxes or this is all for nothing. Those are going to eat up space and add quite a bit of weight.

4. Is there a minimum gap I should leave between walls and ceiling?

You mean how much gap there should be between your iso booth and your apartment walls/ceiling?

Greg

[Kebberj]

Hi Greg,

Thanks very much for your reply. I really appreciate it!!!

You should buy an actual real SPL meter, measure with C weighted and slow setting.

I'll get onto that.

Make this as big as you can and see that your dimensions don't fail Bob Golds Room Mode Calculator tests.

I checked out Bob Golds test and the amroc test. The dimensions fall within the bolt area of the amroc test and the response curve of the Bob Golds test seems OK to me.

Use mass law equation to figure out how much isolation this will give you.

I'm not exactly sure how to calculate this. I found an Excel sheet TL calculator that you made:

http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21373

So I just enter the density of the leaves and the gap and it gives me the TL value - is that right?

Build your room inside out so that you maximize your internal volume and you start with a dead sounding room (all of your walls will be lined with insulation due to the inside out construction)

I've been looking this up to understand it more. My understanding is that you just remove the inner leaf of the booth wall and use the surrounding walls of the existing room as your outer leaf (with insulation between the booth wall and room wall - is that right? Like this:

http://johnlsayers.com/Recmanual/Titles/Acoustics3.htm

Quote:
1. My main concern is sound transmission through the floor below - How can I minimize this? I’ve read on other posts that sitting a booth on a 2” sheet of OC 705 will help minimize transmission. Is that the best option for me?

2. Is a 2x4 framed floor (filled with fluffy insulation) a good idea, or would it be better just to go with thick, layered plywood? Or something else? Or am I doomed because I’ve got wood frames on a wood floor??

I would build the floor out of thick wood with a 2x4 frame around it all sitting on thick 703 or 705. I believe that will be your best chance of decoupling your booth from the floor.

Ok. Do you mean like the floor design in the link below but with the whole structure sitting in 703/705 instead of neoprene pads?:

http://johnlsayers.com/Recmanual/Titles/Acoustics3.htm

4. Is there a minimum gap I should leave between walls and ceiling?

You mean how much gap there should be between your iso booth and your apartment walls/ceiling?

Yeah exactly.

Thanks again for your help Greg!

[Gregwor]

I'm not exactly sure how to calculate this. I found an Excel sheet TL calculator that you made:

http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21373

So I just enter the density of the leaves and the gap and it gives me the TL value - is that right?

The calculator works for a room in a room type construction using the MSM equation.

Since you can't do an MSM due to the extra weight, you would just use mass law equation:

One leaf
Mass Law Equation
TL = 14.5 log (M*0.205) + 23dB
M = surface density in m²
Or
TL = 14.5 log M + 23dB
M = surface density in lbs/ft2

I've been looking this up to understand it more. My understanding is that you just remove the inner leaf of the booth wall and use the surrounding walls of the existing room as your outer leaf (with insulation between the booth wall and room wall - is that right? Like this:

The link you posted doesn't really show it, but here is an inside out room in a room type construction that will hopefully show you what I meant:

Interior%20MSM%20Inside%20Out%20Wall%20Detail.jpg

Ok. Do you mean like the floor design in the link below but with the whole structure sitting in 703/705 instead of neoprene pads?:

I meant like this: (just build a room on top of it instead of a drum kit)

GLENN-example%20drum%20riser%202.jpg

Greg

[Kebberj]

Thanks Greg,

Ok, that floor construction is much clearer to me now. One question: Does the plywood floor sit on top of the wood trim? Or does the trim just get screwed into the outer perimeter of the platform? I can't quite work that out from the diagram.

Cheers,

Kurt

[Gregwor]

Kurt,

Ok, that floor construction is much clearer to me now. One question: Does the plywood floor sit on top of the wood trim? Or does the trim just get screwed into the outer perimeter of the platform? I can't quite work that out from the diagram.

The trim is fixed to the platform. That entire mass "floats" on top of the insulation

Greg

[Kebberj]

Got it. Thanks very much again for your help Greg!

Kurt

[Kebberj]

Hi Greg,

I've been playing around with your MSM TL calculator (which is awesome btw) and I am wondering if, instead of building a drum-riser floor like you suggested, I might be better off building a two-leaf framed floor for my booth (sitting on the 705)? Your calculator is telling me that I'll get way better isolation with MSM, even if the frame depth is shallow (39mm). Would there be any downside to this?

Cheers,

Kurt

[Soundman2020]

I am wondering if, instead of building a drum-riser floor like you suggested, I might be better off building a two-leaf framed floor for my booth (sitting on the 705)? Your calculator is telling me that I'll get way better isolation with MSM, even if the frame depth is shallow (39mm). Would there be any downside to this?

Hi Kurt, and Welcome!

What you describe would basically be a "floating floor". Here's why that's a bad idea:

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

What Greg describes isn't a true floating floor, but it does decouple quite well, in the sense that it stops transmission of impact sounds into/out of the floor, and reduces the transmission of most airborne sounds too. For a typical vocal booth, it's fine.

- Stuart -

[Kebberj]

Hi Stuart,

Thanks very much for your reply. That makes things much simpler for me then! I appreciate the help.

Cheers,

Kurt

[Kebberj]

Hi Stuart and Greg,

I was wondering if I could get your opinion on my current HVAC design for my booth. Going on information from other posts, this is where my head is at:

Booth inner dimensions: (6.25'x4.76'x3.92')
Air volume: 116 cf
6 changes per hour: 696 cfh or 11.6 cfm

I used this calculator posted on Bhudie's recent post to calculate the air flow velocity. I calculated that a register with the dimensions of 2.75" x 3.23" (82cm x 70cm) will give me a velocity of 188 fpm (which is under 300fpm). I then drew up a silencer box design (pictures below) with a cross sectional area that 2x the area of the register. Do these calculations look ok? Assuming it is, what cfm-spec fan would I need to get?

Also, the silencer-box vent goes through the side wall of the booth into an identical silencer box on the outer side of the wall (4 silencer boxes total). I'd like to go smaller on the diameter of the through-wall-vent to make it easier to go around the joist which is in the way a little bit. How small can I go here?

Lastly, in the Sketchups below, I used 10mm thickness for the duct lining. I'm still looking for a suitable material locally in Japan, but I guess it may need to be thicker than 10mm, which I can adjust my design for, but I'm confused as to exactly what's needed here - mass or absorption. I assume absorption, as I see many people with mineral wool lining in their designs, although I've read that exposed mineral wool will release fibers into the airstream. I'm wondering if neoprene sponge or mass loaded vinyl might work? Ultimately I guess dedicated duct liner is the go, but I'm just curious as to what else is possible.

Thanks again for your help!