Isolation Booth for Studio Project Room in Minnesota

[Sunblossom]

Hi guys,

We are new to this forum. I’ve been studying your forum posts, as we prepare to design a custom project room. We are NOT recording studio designers, though we have spent several decades in recording studios, as artists/songwriters/arrangers.

I have the highest regard for your collective knowledge and expertise and very much would appreciate your help. I’ve done my best to provide as much detail as possible. We’re happy to provide additional info.

We are setting up a project room for the purpose of recording two voices (male and female) and acoustic guitar. We are doing this ourselves and would like to end up with something that actually works, which is why we’re here.

We are on a very low budget for this project - under $700. A list of some of the materials we have on hand is at the end of this post.

House

This project room is in a house that was built in 1965. The house is situated on a corner lot. We are rarely bothered by outside noise, as the walls seem well constructed and well-insulated. This project is more about isolating singing voices and acoustic guitar. Wood flooring runs throughout the room and throughout the first floor of the house.


Design of Project Studio

We hope to design the room for two musicians and an engineer.

Our project room needs three small spaces:

1. Control space
Engineer with Macbook Pro laptop, external hard drives, interfaces and 4-way headphone splitter, other small peripheral gear and near field monitors. Some mixing will be done in the engineers control space.

2. Male Vocal/Acoustic guitar isolation booth
The male vocalist is also the acoustic guitar player. He has a VERY loud baritone voice and stomps loudly with his foot when he plays. We lovingly call him Thunderfoot. We’ve joked about strapping his foot to the floor. We need to create an isolation booth for him. There is a possible location for this isolation booth outlined on the SketchUp model.

3. Female vocal space
This space ideally, would be setup so that the male and female vocalists sound like they are in the same “space.” Eye contact between the male and female vocalists is important. They prefer to be tracked at the same time - better performance energy. We need to create spaces that will totally isolate their voices from one another’s vocal microphone, during live takes.


Location of room in house

The project room is on the ground level, above a basement. Two of the walls are exterior walls.


Walls & Windows (See SketchUp model)

Walls A&B both have windows to the outside. These windows are frequently used for fresh air. We would prefer to keep the windows accessible, if possible.

Walls A & B are wood-stud with metal lathe and plaster. They are insulated with fiberglass. On the exterior surface is 3/4” brown fiberboard - buffalo board, with masonite lap siding. (photo)

Walls C, D, and E are wood-stud with metal lathe and plaster.

Wall C divides the room from a hallway. Walls D and E have a living room space on the other side.

Three of the walls in this room are painted with high gloss interior/exterior enamel (B,C, and D) and two are painted with semi-gloss enamel (A&E).


Floor (photos from underneath - taken from basement)

Floor joists are 1-5/16” x 9-1/8” on 16” centers.

Sitting on the joists is a lapped fir underlayment of 1” x 10” s run at a diagonal, 1/2” laps with the boards held back at 1/4” (possibly for expansion).

Sitting on the fir, is 1/8” thick paper layer from the 60’s: tar paper-like in appearance.

Sitting on the paper is 3/4” oak tongue and groove flooring.

On top of the oak tongue and groove is cheap, thin, old carpet.

There is a basement below this room.

From the perspective of a person in the basement - sounds like thundering elephants above, when someone walks across the ground level floor.


Building materials and builder

Greg is a carpenter/fine woodworker, who’s built everything from a beautiful replica of a Martin Parlor guitar, furniture, cabinets, rooms and sheds. He can build most anything out of wood, and works with a variety of construction materials.

We are in a very rural area of northern Minnesota. We have some building supplies available here in town, with Home Depot and Menards about an hour away.

It is always our first choice to repurpose materials we have on hand, before buying new materials.

Materials on hand:

pine dimensional lumber 2’x4’s 2’x6’s 2’x2’s, etc.

70 lengths of 1” x 5-7/16” x 12’ cedar decking

drywall

400 pounds of Quikcrete cement

two old hollow wood panel sliding doors 35” x 75”

double pane glass window, with wood frame 23-1/8” x 34-1/2” x 1-3/8” (photo)

a potential door (22 1/2” W x 6’ 3-1/6” H x 2-1/4” D) for the isolation booth - exterior frame is cedar 2-1/4” x 3/4”, interior frame was made from 3/4” 1”x2” (probably pine) with two 1/2” thick sheets of OSB (oriented strand board - flake board) Could be caulked, sealed, etc. We could also make a second door to match its size, or give up the idea of using it and construct new doors. (photo)

two 4’x6’x3/4” 100% solid rubber mats (photo)

We’ve sourced rock wool for insulation and wool felt carpet padding.

Great Stuff insulating foam sealant

NOTES

We are novices at soundproofing, though we understand the basic concepts of damping, decoupling, absorption, reflected sound, etc. We’ve discussed building the iso booth with non-parallel walls, with two of the walls offset at 12 degrees. We understand that the booth needs to be well-sealed with some provision for air vents so the musicians can breathe.

We often record in this setup and we are willing to go the extra mile to get good clean tracks.

We have a woodworker who can build most anything, a researcher who is willing to do more design homework, and an engineer who would like to get this right the first time, as we are all on deadlines.

This is my first time around with SketchUp. If you right click on a line and select “Entity Info” you will (hopefully) see the exact dimensions as they were measured in our room. I knocked the corner off of one of the walls.

The door to the room opens inward, though we could rehang the door to open into the hall, if the interior space the door opens into is useful in some way.

Questions are at the end of the post below.


Thanks so much!

Kiki


QUESTIONS


What setup for the engineer, male vocal/guitar and female vocal might work in this tiny space? What would you do if this was your room and you needed to get clean tracks from two vocalists singing at the same time?


We understand that the structure of of the floor might prevent floating a floor in the vocal/acoustic guitar booth. What are other possibilities for the floor?


Is the door (photo) we have usable with modification, or should we start from scratch? Is the window usable?

Is the place we've designated for the iso booth on the SketchUp model, the best solution? Is there a better idea?

[Soundman2020]

Hi there Kiki, and welcome!

I downloaded your SKP file, but I couldn't open it as I'm working on an ancient machine where I can't install the latest versions of SketchUp: Please could you save your file as SKP version 8, and upload it to the forum again, so I can take a look.

We are on a very low budget for this project - under $700.

I don't want to sound like a wet blanket here, but for such a small budget there really isn't much you can do in terms of building two iso booths, treating them, and also treating / tuning a control room. Even considering the materials you have on hand, and the skills of your builder for free, I still don't see it as being possible. Just the ventilation fans, lights, and electrics could cost you that much. Alternatively US$700 would be about right for doing minimal treatment of just the control room, to get the worst issues under control. Or maybe for treating one of the isolation booths. But I can't see it extending to doing everything.

I would strongly suggest that you re-think your budget.

I'm not sure how many square feet we are talking about here (as I couldn't open the SKP file...), but I would estimate (very roughly, and please-dont-hold-me-to-it!) that your costs would be in the ball park of US$ 25 to US$ 50 per square foot, for everything you want to do.

But anyway, assuming you can fix the budget issue:

1. Control space
Engineer with Macbook Pro laptop, external hard drives, interfaces and 4-way headphone splitter, other small peripheral gear and near field monitors.

For a control room to have decent acoustics, suitable for "critical listening", the recommendation is for a minimum floor area of 215 square feet. Of course, you can still have a decent control room in less area (I have designed several for spaces considerably smaller than that, and John has even done one inside a shipping container!), but the smaller you make it, the harder it is to treat it, and the more limitations you have. I wouldn't go less than about 120 ft2. Beyond that, it gets to be unworkable.

... and near field monitors.

Which ones? Make and model. It matters, when designing a control room.

He has a VERY loud baritone voice and stomps loudly with his foot when he plays.

... which implies two things: High isolation down to fairly low frequencies (low mids), and impact noise. Low frequencies and impact noise are the hardest problems to isolate. Impact noise gets into the building structure itself, and once it is in, there's no way to get it out again! So you will need some type of "drum riser" type platform for him to stomp on, plus good isolation. That doesn't come cheap.

Also, having an acoustic guitar along with deep, loud vocals, plus heavy foot-stomping, all in the same tiny vocal booth, is going to be a problem. All three of those sounds will be bleeding into each others' mics, quite loud. A larger room would be better for that situation.

We need to create spaces that will totally isolate their voices from one another's vocal microphone, during live takes.

The human voice covers the spectrum from about 80 Hz upwards to about 7 or 8k, or maybe a bit more, so that's where your isolation needs to be good. A screaming human voice can reach about 90 dBC or more, and you'd need to get that to below 40 dBC to make it "really quiet". That would need about 50 dB of isolation.

So you should be planning for 50 dB overall isolation, from 100 Hz upwards (which implies that the MSM resonant frequency of your isolation walls should be somewhat lower than 50 Hz).

above a basement.

Uh oh.... So you are standing on a drum head, basically... a resonant membrane (the floor) stretched tightly over a resonant space (the room below). High levels of isolation are out of the question (unless you float your floor, but that will never happen on US$ 700.... not even on US$ 7,000! Floating a floor properly is expensive...)

Walls A&B both have windows to the outside. These windows are frequently used for fresh air. We would prefer to keep the windows accessible, if possible.

As long as you don't want isolation, sure!

Here's the thing: operable windows imply air leaks. Thin glass implies low isolation. Single-leaf window implies poor isolation, especially at low frequencies- Those things are greatly limiting the amount of isolation you could get.

Floor joists are 1-5/16” x 9-1/8” on 16” centers.

Those were probably originally 2x10's. many years ago, when they were first installed. But what live-load and dead-load are they carrying, and how much extra load can you safely / legally add to that? You will need to hire a structural engineer to answer that question. To isolate, you need mass. Lots of it. You need to be sure that your floor can support the mass without collapsing...

From the perspective of a person in the basement - sounds like thundering elephants above, when someone walks across the ground level floor.

I can imagine! As I mentioned before, it's basically a drum head. Heard from downstairs, it would be like sticking your head inside a kick drum...

Materials on hand:

...

drywall

How much? What type? What thickness?

two old hollow wood panel sliding doors 35” x 75”

Hollow core? No use for isolation, unfortunately. All things "hollow" imply "booming resonance" and very poor isolation. The solid-core door looks more interesting: that might be useful.

double pane glass window,

How thick is the glass, and how thick is the air gap?

two 4’x6’x3/4” 100% solid rubber mats (photo)

What type of rubber? What durometer (Shore)? What scale (00, 0, A, B, etc)? Unless you can find that information, the rubber would not be useful. You can't just use any old rubber for any old isolation purpose! It has to be the correct rubber for the job, such that it will properly "float" the load. If you put too much weight on it, then it over-deflects, bottoms out, and does not isolate. If you put too little weight on it, then it under-deflects, tops out, and does not isolate. The load must be just right to cause it to deflect by the right percentage, and the resilience / thickness must be correct such that the resulting MSM resonant frequency is at least one octave below the frequency you are trying to isolate.

We’ve sourced rock wool for insulation and wool felt carpet padding.

Mineral wool is great, provided that it is the correct density. Carpet padding has practically no uses in acoustics. It's about as bad as actual carpet, perhaps even worse.

Great Stuff insulating foam sealant

Is that an expanding polyurethane spray foam? If so, chances are it is closed-cell, and there has no uses in acoustics.

We’ve discussed building the iso booth with non-parallel walls, with two of the walls offset at 12 degrees.

That's not necessary. It would just waste space, and there's no real need for that in such a tiny space. You'd have to treat the hell out of it anyway, and that amount of treatment would much more than solve any flutter echo issues.

We understand that the booth needs to be well-sealed with some provision for air vents so the musicians can breathe.

Yup! Musicians do seem to like breathing!

Those vents will need fans on them, and also silencer boxes. All of that needs to be calculated to provide the correct volume of air (flow rate) at a low enough speed (flow velocity) that the air itself does not produce noise that would be picked up by the mics. And also to stop sound getting through while still allowing air to get through.

We understand that the structure of of the floor might prevent floating a floor in the vocal/acoustic guitar booth. What are other possibilities for the floor?

Floating that is out of the question on such a small budget. You still would not be able to do it even on a budget ten times larger. Your only other option is a "drum riser" type of floor, which would help considerably with the foot-thumping, but would not be a true isolation floor.

Questions are at the end of the post below.

I can't really answer more than I have without seeing the SKP file...


- Stuart -

[Sunblossom]

Hi Stuart,

Thanks so much for responding.

I downloaded your SKP file, but I couldn't open it as I'm working on an ancient machine where I can't install the latest versions of SketchUp: Please could you save your file as SKP version 8, and upload it to the forum again, so I can take a look.

I've uploaded a version 8 copy of the SKP file.

But anyway, assuming you can fix the budget issue:

We can increase the budget in a couple of ways: cold hard cash and we have two Habitat ReStore centers near us, that specialize in repurposed building materials at very low cost. We like to repurpose, when possible, to keep this junk out of a landfill.

For a control room to have decent acoustics, suitable for "critical listening", the recommendation is for a minimum floor area of 215 square feet.

There are two rooms across the hall:

The smaller is 117.5" x 127.5 (104 sq. ft) and is situated over the basement
The larger is he other 130.5" x 162.5" (147 sq. ft.) is an added room, and is over a crawl space.

The wall between was originally an exterior wall for the smaller room. I think we could put a header in with proper support and open that wall up between the rooms.

Also, having an acoustic guitar along with deep, loud vocals, plus heavy foot-stomping, all in the same tiny vocal booth, is going to be a problem. All three of those sounds will be bleeding into each others' mics, quite loud. A larger room would be better for that situation.

Apologies, I could have clarified this better. We record final vocals on top of the basic rhythm tracks, whatever they may be. His isolation booth needs to be large enough for him to record, separately, both his final acoustic guitar tracks and his keeper vocals. They are recorded independently, though the male and female vocals are almost always recorded simultaneously, which is, of course, where the problem with bleed through happens.

For a control room to have decent acoustics, suitable for "critical listening", the recommendation is for a minimum floor area of 215 square feet.

Perhaps we should consider the suite across the hall. (251 square feet total)

Which ones? Make and model. It matters, when designing a control room.

These are old Event Project Studio 5s. We plan to upgrade.

So you should be planning for 50 dB overall isolation, from 100 Hz upwards (which implies that the MSM resonant frequency of your isolation walls should be somewhat lower than 50 Hz).

Good information to have. Thank you!

Here's the thing: operable windows imply air leaks. Thin glass implies low isolation. Single-leaf window implies poor isolation, especially at low frequencies- Those things are greatly limiting the amount of isolation you could get.

Well, you are right, of course. Moving the studio across the hall, would put it on the north side of the building. I could live without the windows on that side. This is northern Minnesota, where we treasure ever drop of sunshine.

So you are standing on a drum head, basically

Yes, exactly!

To isolate, you need mass. Lots of it.

We could probably put the kind of weight you're talking about in the added room, though we'd have to crawl under the house and see how to reinforce the floor. Greg is mentioning a post and beam (on pier pads) reinforcement of the existing floor in the 130.5" x 162.5" (147 sq. ft.) room over the crawl space.

[Drywall] How much? What type? What thickness?

5/8" thick, 4'x12' and 4'x8' USG fireproof gypsum as much as we need.

Hollow core? No use for isolation, unfortunately. All things "hollow" imply "booming resonance" and very poor isolation.

Good to know. We'd thought of peppering the doors with holes and filling it with crack sealant to dampen them. We'll let go of the idea of using them.

Is that an expanding polyurethane spray foam? If so, chances are it is closed-cell, and there has no uses in acoustics.

Yes, I think that's right - polyurethane

[double pane glass window] How thick is the glass, and how thick is the air gap?

Greg is approximating - best guess is gap of 1/2" two panes 1/8" each.

What type of rubber?

No idea. they did not come with a label. Very stiff, for rubber.

Mineral wool is great, provided that it is the correct density.

Roxul Safe 'n' Sound 3 in. x 15-1/4 in. x 47 in. Soundproofing Stone Wool Insulation (12-Roll) Either 6lb or 8 lb - not sure which our Home Depot has.

That's not necessary. [non-parallel walls] It would just waste space, and there's no real need for that in such a tiny space. You'd have to treat the hell out of it anyway, and that amount of treatment would much more than solve any flutter echo issues.

Good to know!

Your only other option is a "drum riser" type of floor

I'll research this. Thank you.

Thanks again for taking the time to respond to my post. I really appreciate it!

Kiki

[Sunblossom]

Since reading your response, we've reconsidered the location of our project studio space, and have decided to move this project to the other two rooms mentioned in my last post.

The smaller is 117.5" x 127.5 (104 sq. ft) wood floor and is situated over the basement
The larger is the other 130.5" x 162.5" (147 sq. ft.) wood floor is an added room, and is over a crawl space and earth.

The 5" wall between the two rooms was originally an exterior wall.

We're tearing out carpet this weekend and have been scraping up carpet adhesive off maple wood flooring.


Question:

We're thinking of using one space for a control room and the other space for creating two isolation booths. Would you recommend using the larger room for the control space and the smaller for the isolation booths?

[Soundman2020]

Would you recommend using the larger room for the control space and the smaller for the isolation booths?

Definitely, yes! 147 ft2 is still on the small side for a control room, but much better. You should be able to get decent acoustics in that size and shape room.


- Stuart -