Detached garage conversion to podcast/audiobook studio

[RHF]

I am converting my 22' (6.7m) by 19' (5.8m) detached garage to a podcast/audiobook recording /editing studio and am looking for some advice from you all.

A couple of notes:
This is a multifunction space so I can't make unilateral decisions for soundproofing.
Earthquake country here so local codes require significant bracing.

Here is my current plan for external walls (exterior to interior):
Stucco
Sheathing
building paper
studs
insulation
shear wall 1/2" plywood (require bracing for earthquakes)
Hat-channel furring
two sheets of 5/8" sheetrock with green glue between

Garage studio construction detail.jpg

Greetings!

This makes for a 7" wall but I'm concerned I'm not configuring it correctly.

I know the right angles are heresy but I can't sacrifice the floorspace quite yet. Also, the sliding door is negotiable and I don't know a better solution.

Will the wall plan be sufficient?
Advice/thoughts?

Thank you!

[Soundman2020]

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

This is a multifunction space so I can't make unilateral decisions for soundproofing.

What other functions does it have, and why do those functions prevent you from isolating it from the outside world sufficiently that you can successfully record podcasts and audio books?

Earthquake country here so local codes require significant bracing.

Take a look at my profile, to see where I live: We certainly have a lot in common! Those regulations are very, very necessary.

Stucco
Sheathing
building paper
studs
insulation
shear wall 1/2" plywood (require bracing for earthquakes)
Hat-channel furring
two sheets of 5/8" sheetrock with green glue between

That would give you very lousy isolation, since it is a 3-leaf system with a very thin air cavity and no damping on the final leaf, with all three leaves firmly tied together, and no decoupling at all. Plus, your description does not match the image you posted.

It's also rather strange that code requires the sheer member on the inside of the studs, and only 1/2" for seismic stresses? Are you sure that is correct? That would not pass inspection where I live. The sheer plane normally goes on the OUTSIDE of the studs (the exterior side), and the sheer member should be thicker than just 1/2". 5/8" or even 3/4 would be better, and OSB would be better than ply, if code allows that. The CORRECT way of building such a structure would be:

Stucco
Wire mesh
3/4" OSB or marine grade structural plywood as sheer member
building paper
stud frame with insulation in stud bays
RSIC clips with hat-channel
two sheets of 5/8" sheetrock with green glue between

That would be for moderate isolation needs. Even better, for higher isolation, would be:

Stucco
Wire mesh
3/4" marine plywood or OSB as sheer member
building paper
stud frame with insulation in stud bays
gap
stud frame with insulation in stud bays
5/8" OSB
two sheets of 5/8" sheetrock with green glue between

This makes for a 7" wall but I'm concerned I'm not configuring it correctly.

How did you get to 7"? Are you using 2x6 framing? The diagram shows 2x4... but then again, the diagram shows a different wall from the one you describe.

I know the right angles are heresy

Not true! You have been reading in the wrong places, and you have been mislead. It's a myth that studio walls must not be parallel: there's no reason at all not to have a rectangular room! Many, many studios are rectangular. Perhaps the best known (and one of the best in any case) is Abbey Road: Everything is rectangular.... So wherever you got that information that studios must have splayed walls is dead wrong, and you can safely ignore it. They CAN have splayed walls, and there are reasons why you might want that, but it is NOT a requirement.

Will the wall plan be sufficient?

Sufficient for what? You didn't say how much isolation you need, so it's impossible to say. All I can say is that if you built it the way you described it, it would have poor isolation, especially in low frequencies. The type of frequency you would expect from your neighbor¿s lawn mower, traffic driving past, aircraft flying over, rain, hail, thunder, wind, dogs barking, radios playing, and suchlike.

Advice/thoughts?

Your control room is way too small to be usable. The minimum spec is 200 ft2 of floor area. That doesn't mean that you can't have a room smaller than 200 ft2, but it DOES mean that it will be harder and harder to treat, the smaller it is. But 36 ft2? That's not a room: that's a closet! There's no way that you can get usable control room acoustics in a room that small. The smallest one I have ever designed is around 100 ft2, and that is extremely tiny. It was a major challenge to design that with usable acoustics. Huge amounts of treatment: the treatment alone fills about one third of the total room volume, leaving about 65 ft of actual usable floor. If you start out with 40ft, you would need to use about 3/4 of that for treatment, leaving you with maybe 10ft of actual floor area... and even then it would sound pretty bad. The smaller the room, the more treatment it needs.

So my first advice would be to re-design your layout so that the "future control room" can actually have enough space to be usable as a control room.

Considering that this is studio is just for podcasts and audio-books, with no need for tracking musical instruments, I would also suggest that the control room could be the ONLY room that you need! There's no need for a large vocal room for simple VO work. It is entirely feasible to track voices in the control room.

My next advice would be, if you do want to use the main area for recording, and you need decent isolation, then move that support column in the middle of the floor. You'll need to hire a structural engineer to come look at that and tell you what you need to do to get rid of it, but I would imagine that an LVL or RSJ across the room at ceiling height would do the trick, or maybe you might need to put a heavier ridge beam in, with support columns at either end. If you did that, you could also modify your trusses to be raise-tie or color-tie, and gain a lot of ceiling height. I have done that in a few studios, and it's not as scary as it sounds.


- Stuart -

[RHF]

Thanks Soundman2020

A few thoughts:

Other uses for this space: Guest house for visitors. Play / Art workspace for children as they grow.
The usable square footage is important so that is the main limitation presented by the other uses.

I'll take another look at the codes to see if I need thicker than 15/32". It's a rather lightweight structure which but there is a second floor which is a small apartment. I'm trying to do the work without hiring an engineer as we are making it stronger than it was by building a wall where the garage door was and adding continuous sheathing to the whole structure. Once again, budget is at play. Also, getting rid of the center post would require engineered plans and additional foundation work. Our engineer estimated $20k for similar work. Contractors are very expensive up here.

Wall thickness:
stucco + sheathing = 2 1/2"
2x4 framing = 1.75"
furring and iso clip = 1 5/8"
2x 5/8" drywall = 1 1/4"
total:7 1/8"

Good to know I don't need to be too concerned about right angles. I assumed it was to mitigate parallel walls which result in standing waves. If treatment can solve this then great.

I live in a moderately dense neighborhood with minimal air traffic but significant street traffic 125' away. It's pretty quiet back there but neighbors talk and use power tools on occasion. More importantly is the isolation from footfall traffic from the apartment overhead. I don't have ceiling clearance to truly solve this issue but I was planning on doing hat channel, iso clips and double drywall with green glue for the ceiling as well.

Re: the control room, I was thinking of it more as a private space with a window looking into the recording area. Since podcasts/audiobooks are primarily headphone experiences, that would be the critical monitoring method. The control room in this instance would basically be for a producer so they could eat their lunch, tap away on their keyboard, have a private (quiet) phone conversation) and still be able to talk back and forth to talent as needed, all this while talent is reading for hours on end. I would wall off the laundry area in that instance. The control room monitoring will surely suffer due to size as you point out.

Is there another wall configuration you might recommend for the exterior wall that preserves the existing stucco? I'd like to keep the stucco exterior and 2x4 framing. My main concern was the drum effect due to the two air cavities but I can't figure out how to fix that without major renovation. I can't really stand to lose much more floor space but I'm hoping someone will have a great idea on how too plan it better.

Thank you!

[Soundman2020]

I'll take another look at the codes to see if I need thicker than 15/32". It's a rather lightweight structure which but there is a second floor which is a small apartment.

In that case, I would definitely go with something more substantial. Having been through quite a few 6.x quakes, a handful of 7.x quakes, and a couple of 8.x quakes myself, I'm very much aware of just home much stress and movement this type of structure has to deal with. Your area hasn't been hit with quite such big ones yet, but they do keep on talking about "the big one" that is coming some day. I'd make sure that your place stands a goo chance of surviving that, by beefing it up decently while you have the opportunity.

I'm trying to do the work without hiring an engineer

You should probably reconsider that. Yes he will charge you money, but your life is on the line here. You might also find that your home-owners insurance policy will NOT cover any damage or injuries at all if you make unauthorized modifications to your place, and then it collapses in the next quake. That makes you personally liable for all damages and injuries, both civilly and probably criminally as well. It's really not worth putting yourself in that situation. Spend the few hundred bucks it will cost you to get the signed professional opinion of a qualified structural engineer. By all means do all the design yourself, but then call him in to check it, and make whatever modifications he recommends. It's cheap insurance! And it might also save your life, or the lives of your loved ones. I have personally seen what a quake can do to a structure that was not properly prepared for seismic loads: it's not a pretty sight.

Wall thickness:
stucco + sheathing = 2 1/2"
2x4 framing = 1.75"
furring and iso clip = 1 5/8"
2x 5/8" drywall = 1 1/4"
total:7 1/8"

So you are going with a single-framed wall with iso clips, instead of a double framed wall? That will work, yes, except that you do not need furring on the iso clips: you need hat channel. Sometimes people do call that "furring", yes, but more correctly it should he called "hat channel", for clarity and to avoid confusion.

Also, that will work provided that you only need moderate isolation: if you need high isolation, then you would need to make that into double-framed wall, in which case you skip the iso clips and hat channel: just put the second leaf drywall on one side of the second frame. Better still, put one layer of OSB on the frame, then a layer of drywall on top. Once again, that gives you much better sheer strength in the inner leaf, plus you then have a nailing surface around 100% of the room.

Good to know I don't need to be too concerned about right angles. I assumed it was to mitigate parallel walls which result in standing waves.

That's a myth. Parallel walls do not create standing waves: ALL walls create standing waves, parallel or not! Sometimes you do see incorrect advice on websites and forums about how it is necessary to "angle your walls to get rid of modes", but that is simply not true, and is a bad idea anyway. Its a basic misunderstanding of what modes actually are. In simple terms, a "room mode" is just a path that a sound wave can take around the room, then arrive back at it's starting point going the same way as it started, and in phase with itself. It's that simple. Modes occur in ALL rooms, not just ones with parallel walls. In fact, the worst possible modal problem you can create, is if you build your room as a sphere! A sphere has no parallel walls at all, but is sure as hell does have MAJOR modal problems, because ALL possible paths around the room are modes that occur a the exact same set of frequencies. The next worst is a cylindrical room, followed by a room with any concave shaped walls, then a cube, then a rectangular room with related dimensions, and finally the least problematic is a rectangular room with un-related dimensions.

Splaying your walls does not "get rid of" modes: it merely moves them to a different frequency, which will probably be higher than the original, since it will likely change the mode from being a single "axial" mode to being one or more "tangential" modes, which means it involves four walls instead of two, or it could even become one or more "oblique" mode, which involves all six walls (where "wall" includes "ceiling" and "floor").

It is impossible to get rid of modes by angling the walls. The ONLY way to get rid of the modes in your room, is to get a bull-dozer and destroy all the walls! The only place you can mix in an environment that has no modes at all, is out in the middle of the countryside, with no trees, malls, or anything else around you for 60 feet in any direction, and sitting on top of a 60 foot ladder. There will be no modes that can affect you like that.

Modes (standing waves) are a consequence of having walls, plain and simple. If you have walls around you, then you have modes forming between them. regardless of the angles of the walls.

Some people look at all that, then think: "Cool! I know that low frequency modes are a problem, and that splaying my walls will push them to a higher frequency, so I'll splay all my walls and thus get rid of all of those pesky, bad, evil low frequency modes!". Wrong! Totally and completely wrong. The problem with the low frequency modal response of a small room is NOT that there are too many modes, but exactly the opposite: there are not enough modes!

It's a bit complicated to explain, but that's the truth

I wrote a long explanation about how all this works a while back. If you are interested, I'd be happy to dig it out again and put it here, in your thread. Let me know if you want that.

Splaying your walls can help with a totally different issue, absolutely unrelated to modes: flutter echo. But flutter echo can be dealt with using other methods, so it's not an issue.

If treatment can solve this then great.

In a reasonably large room, it is possible to damp the low end with a small amount of treatment, so that you get very smooth response, resulting in tight, clean bass and no artifacts. In smaller rooms, you can get close with stacks of treatment, but there are limits. In very small rooms, it isn't possible. The smaller the room is, the harder it is to treat, and the less likely it is that you will get fantastic results.

I live in a moderately dense neighborhood with minimal air traffic but significant street traffic 125' away. It's pretty quiet back there but neighbors talk and use power tools on occasion.

You should get out your sound level meter, and measure that. Use "C" weighting and "Slow" response. You need to know how loud that is, so you can design your isolation system accordingly.

More importantly is the isolation from footfall traffic from the apartment overhead. I don't have ceiling clearance to truly solve this issue but I was planning on doing hat channel, iso clips and double drywall with green glue for the ceiling as well.

That will certainly help, yes, but for impact noise like that, the very best treatment is to prevent it from happening! Just carpet the floor above. But down a good thick, soft underlay, and good thick carpet. Even if that is not your place, and not your responsibility, it is still very much worth your while to pay for it. The problem is that impact noise is structure-borne, and that's really hard to deal with. And really expensive! Much better (and cheaper) to simply kill it at the source.

Re: the control room, I was thinking of it more as a private space with a window looking into the recording area. Since podcasts/audiobooks are primarily headphone experiences, that would be the critical monitoring method. The control room in this instance would basically be for a producer so they could eat their lunch, tap away on their keyboard, have a private (quiet) phone conversation) and still be able to talk back and forth to talent as needed, all this while talent is reading for hours on end.

That sounds more like an office than a control room!

- Stuart -

[RHF]

Thank you again, Stuart, for your insight. I have been chipping away at planning this and can see I still have improvements to make. I'll set up an audio recorder with a calibrated mic in the back yard and gather some detailed noise profiles so I can address my actual isolation needs and not guess wildly.

In the meantime, I will reach out to some structural engineers to see if there are any sound savvy ones available and interested in the project.

Since I don't have the floorspace to sacrifice for a proper triple leaf scenario, I'm considering the following configuration and would like input:
Existing stucco
2x4 framing with Roxul insulation (considering ecowool)
5/8" structure-1 OSB (thickest our lumber store carries)
Green glue (2x normal)
5/8" sheetrock (type recommendation?)
Green glue
5/8" sheetrock

Another sticking point is the bathroom exhaust fan. It will be in the ceiling and it seems like it'll have to vent immediately out the adjacent wall as a mere few feet away. Basically the vent tube will only fit between the ceiling/floor joists and seems like it would require significant work to do anything else. My cursory insderstanding is that I can decrease sound leakage in from the vent by using an indirect path but that doesn't seem to be an option here. Basically there's 7.5" between the subfloor and the ceiling and cutting the floor joists is above my pay grade (especially given earthquake country). Should I baffle the exit point outside instead?

Is there a standard recommendation for sealing around plumbing pipes etc?

Also I'm planning on replacing the existing waste lines that come from upstairs with cast iron as I expect it to be much quieter than the existing copper (Yes Copper!).
So much ilarly, is there a sound specific recommendation for quieting supply lines? Is standard pipe insulation the best idea?

I'm picking up Recording Studio Construction by Newell to have as a handy reference so maybe these questions are folly when it probably has solid recommendations.

I took out my previously planned ceiling lighting and will use switch controlled floor lamps instead.

I'll get some real noise measurements going soon.