John Sayers' Recording Studio Design Forum Archive

I've been enjoying the information on this site, but this post is my first attempt to gain some custom advice on the studio project that I am planning to start this Summer. The basic idea is a nice big practice room in a new garage-like structure in my backyard.

Since this is my first post, I'll start with an introduction. My name is Adam and I'm a Software Engineer living just outside of Baltimore, MD, USA. I became interested in recording and acoustics in college when I would do amateurish live sound and recording for rock bands (including my own) in college. I decided to buy a house last year so that I could have a purpose built rehearsal and recording space. I've skimmed through Rod Gervais's Home Recording Studio book and numerous internet resources like this forum, and I'm pretty confident that I could make a good space with what I know - I'm hoping the advice I get from this forum will help me make a *great* space.

USE CASES:
The primary use case of the room would be providing pleasing acoustics and recording capabilities for small music ensemble rehearsals. Styles would range from heavy rock (drum kit, guitar, bass, synth), to classical (small chamber orchestra), to jazz (trio maybe with horn section). In other words, it should be able to fit as many as 15 musicians (bad cramped case), be optimal for ~5 musicians, handle ~120dB volume levels, and provide ~45 STC isolation from the outside (lawn mowers and the trains a few blocks a way are the main noise concerns).

The secondary use case would be a mixing room. I'm not 100% sure how to balance the mixing room needs with the live room needs.

The tertiary use case would be a home theater. Why not, in a big, nice sounding room?

LIMITATIONS:
My budget is ~$40,000 USD, but I don't have all of that right now - I'm planning on getting the guts up this summer, and spending a year or two adding the fancy stuff. I'll have ~$20,000 to work with this summer.

I am a DIYer with limited construction experience, but I want to do most of this (everything but the slab) myself to build up my skills.

THE PLAN:
I'm going to start with a concrete slab foundation that's ~20somethingx20something. My yard is 50' wide and 177' deep, and I'd only want to use a maximum of about 30' of that depth. Part of the floor space will be for "utility" items (computers, electrical sub-panel, bathroom, air handler, kitchenette(?), etc), and the rest would be for the studio. I don't have too many details (short of copying common advice from the gervais book and the internet), and I've reached a point where I'm having trouble deciding on room dimensions.

THE MAIN QUESTION OF THIS POST:
With a room size around 20x25x9, would it be worth the effort to make non-parallel walls and ceiling? Is it possible to design a non-parallel space that performs worse than a parallel space of similar volume with good dimensions? I'm trying to keep it symmetric (for the mixing room and home theater use cases).

My pictures are from HomeDesigner - I know you guys usually use SketchUp, but the tutorials make it seem pretty hard to make a basic building with default measurements for walls and doors and stuff. Is there a plugin that makes that easier?
For either of those designs, would a slanted ceiling be reasonable? I was thinking I could do a shed roof that slants up towards the back (wider) end of the room.

Thanks,
Adam

Hi Adam. Happy New Year, and Welcome!

numerous internet resources like this forum, and I'm pretty confident that I could make a good space with what I know

Careful with some of those resources! Like most things on the Internet, there's some really good stuff, a lot of mediocre stuff, and a ton of really lousy stuff! A lot of the "How I built my studio" videos on YouTube, for example, fall into the latter category...

I'm hoping the advice I get from this forum will help me make a *great* space.

Yup! You came to the right place, for sure, if you want a high quality studio.

The primary use case of the room would be providing pleasing acoustics and recording capabilities

Can you try to define that a little better? Is it mostly a rehearsal space where you would very occasionally do a simple demo recording/mix? Or is it mostly a mixing space, where you'll have the occasional rehearsal?

Have you also considered the possibility of having two rooms? A large "Live Room" for rehearsal and tracking, plus a smaller control room for mixing? With 740 square feet (shown on your diagram), you have PLENTY space to do that. I have designed quite a few two-room studios in much less space than that, also including a bathroom and kitchenette. I'm just finishing up the details for one like that in New Zealand, in less than 450 square feet, there's one under construction in Australia right now at a little under 500 square feet with a large CR and a small drum booth, one nearly completed in California a little over 650 ft2, with a very large live room, small control room, bathroom, and lobby: and I've done a few other similar ones. 750 ft2 is plenty to do that. Even 600 ft2 would be good. With careful design, you could fit in all of what you want, plus more, and make it all sound great!

it should be able to fit as many as 15 musicians (bad cramped case), be optimal for ~5 musicians,

A word to the wise: your HVAC system is going to need careful attention, since you will need to account for cooling and dehumidifying that room when it is full of 15 hard-jamming sweating heavy-metal rock musicians plus their instruments, gear, lights, etc... and also for the situation where you have one lone musician playing gently, all by himself. Vastly different air handling requirements. Something you need to take into account.

The secondary use case would be a mixing room. I'm not 100% sure how to balance the mixing room needs with the live room needs.

It is possible, to a certain extent, but you need to decide which is your priority. The ideal acoustics for a control room (CR) is flat response, both in frequency and time domains, whereas the ideal response for a live room is for it to have some character, longer reverb tails, life, warmth, etc. Mixing in a room with non-flat response is a challenge, and playing in a room with dead flat response is not much fun. One option is to build variable acoustic panels so you can change the acoustic response of the room, but that's rather more complex. I have done that for live rooms, to be able to change it for different situations, but I'm not sure I'd want to risk it in a control room. It should be possible, but .... hmmmm... big challenge!

The tertiary use case would be a home theater. Why not, in a big, nice sounding room?

A control can indeed be used as a home theater! Very similar acoustic requirements.

My budget is ~$40,000 USD, but I don't have all of that right now -

The budget is reasonable, but maybe a little on the low side for a complete ground-up build, even if you do most of the labor yourself. And if you don't have a lot of experience in construction, you might not be able to do lots of it. Electrical, roofing, HVAC, concrete, glazing... those things where you might need help, not only practically but also legally. Question: Among your musician friends, might there be any tradesmen who would be interested in exchanging some of their skills for free sessions in the studio, once it is complete? Maybe there's a qualified electrician who can sign off all the electrical work? Maybe a qualified structural engineer, or architect who can do likewise for that part of the build? There's a lot of paperwork that needs signatures from people with various certifications, and those signatures cost money if you have to hire people to do the work for you, but could happen for free if you have the right friends!

Part of the floor space will be for "utility" items (computers, electrical sub-panel, bathroom, air handler, kitchenette(?), etc)

The AHU can go overhead, above your storage area or kitchenette, so it does not need to take up any floor space, and the electrical panel can be on the wall in the lobby/kitchenette area, if you design carefully.

With a room size around 20x25x9, would it be worth the effort to make non-parallel walls and ceiling?

That's the 64,000 dollar question, isn't it? But at the same time, that's sort of like asking: "With a road about 300 miles long, should I get a Toyota, or a Ford, or a Jeep?". It all depends on what the road is like, what you want to take with you, and what you want to do along the way, etc.

In other words, the answer is "Yes, no, maybe, never, always".

Not much help!

But it works like this: there are only three valid reasons for splaying your walls. 1) To avoid flutter echo. 2) because you are building a control room based on the RFZ, CID, NER or other similar principle that rely on angled walls. 3) Because it looks cool!.

That's it. Acoustically, there really aren't any other valid reasons. Now, for the first one, you can get rid of flutter echo with simple treatment, and since you'll need treatment anyway (it goes without saying), you don't really need to splay your walls for this reason. And if you do want to do this for flutter echo, you need a total difference in angle of at least 12°, which could be 6° on two opposite walls, or 3° on one and 9° on the other, or 12° on only one, or whatever combination you like. However, large angles like that waste a lot of space, as you can see on your own initial design. So it is best not to.

For the second reason, in my option this is the only truly valid reason for splaying walls. RFZ is arguably the best design concept currently available for control rooms, and it is based on angling certain parts of certain walls at certain angles, to ensure that the sound at the mix position is as clean as possible. If you wanted a really good CR in your studio, then that's what I would do. But you do NOT need that in the live room / tracking room / rehearsal room (or whatever other name you want to put on it). You CAN if you want, for reason #3, but acoustically there isn't a need for it.

Now some people say "But all great studios must have angled walls! I read it on the internet!". To that, all I can say is: "Garbage": Take a look at Abbey road. Nobody would argue that their studios are bad, or even mediocre: in reality, they are considered among the best in the world! And they don't have a single angled wall anywhere... Case closed.

In other words, it is a myth that you need to angle walls, except in the specific case of control rooms built to a specific design philosophy that requires it.

So, to answer your question more intelligently: IF you do decide to put a control room in there, then yes, absolutely: build it as an RFZ-style room, and angle the walls accordingly. Id doing that means that one or more of the live room (LR) walls also ends up angled, then fine. But if you decide to just have a single large room that is to be 90% for rehearsals, with only 10% for the occasional simple low to medium quality demo mix, then no you do not need to to do that.

Is it possible to design a non-parallel space that performs worse than a parallel space of similar volume with good dimensions?

Oh, yes, absolutely it is! I've been in some non-parallel rooms that sounded really terrible, and I've been in some similar sized purely rectangular rooms that sounded fantastic. You can design any sized room badly, from the acoustic point of view. And most sizes of room can also be designed to sound good acoustically, or at least acceptable, even for relatively small rooms. John has designed great rooms that fit inside a shipping container!

I know you guys usually use SketchUp, but the tutorials make it seem pretty hard to make a basic building with default measurements for walls and doors and stuff. Is there a plugin that makes that easier?

It is actually very, very simple to do walls, floors, ceilings, doorways and windows in SketchUp. It's a very powerful tool, and is well worth the effort to learn. There are some quirky things that you need to figure out when you get started (such as ALWAYS making each item into a "component", never leaving it as a bunch of individual surfaces), but once you figure that out, it is dead easy.

Here's your same model, in Sketchup:
It took me all of one minutes and 30 seconds to do that. Here's the actual model:


I bet it took you a lot longer than that to do yours!!!

For either of those designs, would a slanted ceiling be reasonable? I was thinking I could do a shed roof that slants up towards the back (wider) end of the room.

You could do that, yes. Doing the trusses for a shed roof is perhaps a bit easier, but there's a lot to be said for gabled roofs... especially if you do a raised collar truss: that can leave you with plenty of space overhead for your HVAC, which is always a problem to fit in in most studios. It can also give you more ceiling height in the LR, where you need it most.

Are you limited to 9' ceilings? Would it be possible to go for something higher than that, or is this a local code issue? If you can go higher, that would be great. It would be a shame to have a nice large 450 ft2 live room with a relatively low ceiling....

- Stuart -

Thanks for the quick and thorough reply. I definitely have the confidence to make a more detailed plan now, and you've given me a lot of great bonus ideas to boot.

Can you try to define that a little better? Is it mostly a rehearsal space where you would very occasionally do a simple demo recording/mix? Or is it mostly a mixing space, where you'll have the occasional rehearsal?
Have you also considered the possibility of having two rooms? A large "Live Room" for rehearsal and tracking, plus a smaller control room for mixing?

My current priority is practicing and rehearsals, but I'm fickle, so I should probably plan ahead for when I am more interested in having a nice CR. My future plans will probably start including a two room option...

The budget is reasonable, but maybe a little on the low side for a complete ground-up build, even if you do most of the labor yourself.

I'll take your word for it - my estimator skills are even less trained than my construction skills at the moment. I can afford to go higher, but I'd like to keep my aim at the $40,000 figure, so maybe I'll make some size compromises. I don't have any contacts that would be able to help me lower that price at the moment, so I can't really plan for that.

So, to answer your question more intelligently: IF you do decide to put a control room in there, then yes, absolutely: build it as an RFZ-style room, and angle the walls accordingly. Id doing that means that one or more of the live room (LR) walls also ends up angled, then fine. But if you decide to just have a single large room that is to be 90% for rehearsals, with only 10% for the occasional simple low to medium quality demo mix, then no you do not need to to do that.

This answers my main question very nicely.

I bet it took you a lot longer than that to do yours!!!

Maybe by a little - I'll keep trying to learn both and see if the learning curve difference is worth the cost of the HomeDesigner license when my trial expires.

Are you limited to 9' ceilings? Would it be possible to go for something higher than that, or is this a local code issue? If you can go higher, that would be great. It would be a shame to have a nice large 450 ft2 live room with a relatively low ceiling....

I definitely want tall ceilings - I'm going to try to work that into my next plan. Speaking of which, I'll probably get a more detailed plan up within a week or so. What's the normal procedure for evolving plans? Should I post new plans/questions related to this project to this thread or start a new one?

What's the normal procedure for evolving plans? Should I post new plans/questions related to this project to this thread or start a new one?

It's best to keep it all together in one thread: all your questions, photos, diagrams, models, updates, etc. Then later, in a few months, when you start the actual build, I'll move the same thread over to the Build forum, where you can continue to add to it, and use it to document the construction process, as sell as ask more questions along the way, then design and build your treatment at the end, to tune your room(s).

But the single most important thing you can do, is to first complete your design very, very carefully, in 3D, with all details, double-checked and triple-checked. Building a studio is mostly about designing it properly: the actual construction is easy. It's the design that is hard. Unless you don't design it well, of course: in that case, the design is really simple, and the construction is a nightmare!

- Stuart -

I've been delayed talking to the zoning people and renovating my bedroom, but things are mostly good to get back on track. I'm thinking of hiring a general contractor to build the external structure nice and fast in the spring so that I'll have more time in the summer to work on the insides. Does anyone have experience hiring someone for just the structure, and are there things to watch out for that aren't obvious? It seems like I just need to make sure that the walls and ceiling will be high enough, and the frame will support the right amount (2 leaves?) of drywall.

Some of the bad news from the planning/zoning people is that only a licensed electrician can install *any* wires that have *any* voltage. I suppose I could try to find somebody to install all the power and audio cables, but I might try to design around this (optical cables for audio between rooms? big tube between control and live room holding "temporary" cables?)

Hopefully I'll get my next draft up this weekend.

I'm thinking of hiring a general contractor to build the external structure nice and fast

I would suggest that you complete the entire design first, before you start building anything. Lots can change in the course of the design. You might even need to change the size/shape of the slab, or the thickness, of the positions of doors / windows. When I'm designing, that happens a lot: the original concept that I start out with often changes quite a bit as I get into the details, and notice things that can be improved, or compromises that need to be made. I would suggest that you don't build anything at all until the design is absolutely final.

Does anyone have experience hiring someone for just the structure, and are there things to watch out for that aren't obvious?

The most obvious thing is that the entire outer structure must be fully sealed, airtight, completely hermetic, and that there is enough mass (surface density) to create the needed MSM conditions for the required isolation.

It seems like I just need to make sure that the walls and ceiling will be high enough, and the frame will support the right amount (2 leaves?) of drywall.

You won't know how high the walls have to be, nor how much mass you will need on the outer leaf, or the inner leaf, until the design is well advanced.

big tube between control and live room holding "temporary" cables?)

Conduit is ALWAYS your best bet. Put plenty of conduit between the rooms, make it large diameter, and make sure that it has the necessary breaks and decoupling to prevent flanking. Keep the curves wide (so not use elbows!). put in more than you will need, and run fishtape through all of them. Keep the electrical conduit away form the signal conduit, following the usual precautions.

- Stuart -

I started working with sketchup and I really like it - thanks for the recommendation.

I'm working on a general idea for an interior space plan first - there's still some basic things to work out (exterior wall STC strategy, finalizing a required STC), but I just thought I'd post the progress to make sure there aren't any major misunderstandings. Are my placeholder conduits far enough apart? Is having one big arc taking the "no elbows" advice too far? Would they be metal or pvc? Could I do the conduits through the walls to simplify the slab construction?


EDIT: I'm actually going to do the conduits through the walls.

I ran into a bunch of permit issues with my county, so here's what I'm working with right now:

A 24.5'width x 25' depth x 10' height (13' middle height with scissor trusses) "garage" with a garage door on the front, and the framing for a second garage door on the front (so that I can convert it into a 2 car garage in the future, if desired). Only electrical - no plumbing allowed. I'm thinking about having the contractor also build the framing and one layer of drywall for the room-in-a-room structure on the inside. I'll figure out how to optimize the dimensions for live/mixing hybrid room later, I'm just trying to get a few loose ideas hammered down.

I'm planning on doing exchange chamber style HVAC (any recommendations for products/designs would be appreciated)

I was thinking about getting a garage door that had a decent STC. Would this be a waste due to the inevitable air gaps and other parts of the garage's basic external structure? I wasn't going to force/expect the contractor to achieve a high STC rating on the outside walls - he mentioned that he didn't have too much experience with it, and that makes me think it would be bad or expensive for me to get him and his team to try things they don't normally do, like exterior gypsum sheathing.

Is there even a point in shooting for a very high STC on the walls of the room-in-a-room structure if I'm going to have conduit and ducts and a door? Won't the ducts and conduit through the walls (even when they're the expensive stuff installed perfectly) have a maximum STC in the 30-40 range? I was thinking about trying out 1 layer of air-sealed drywall to see if that works well enough to pass the "lawnmower outside the garage" test. I'd be comfortable doing the second layer myself later with green glue or something, but that wouldn't really help if everything could still get through the ducts.

Do I need to give the contractor any special instructions for the room-in-a-room drywall install? would they do the normal mudding and taping, or should they be using some kind of soundproofing product on the seams?

Thanks!

Apparently some garage doors do have a decent STC: http://www.clopaydoor.com/Pressreleases ... -fire-door

Correct me if I'm wrong - that (STC 27) would about match an exterior gypsum and OSB sheathing layer.

I ran into a bunch of permit issues with my county,

Bummer! But at least you have come up with a work-around.

I'm planning on doing exchange chamber style HVAC (any recommendations for products/designs would be appreciated)

So you will be building an extra "room" (or at least "very large closet") for that purpose? You still need to isolate the ducts that lead into and out of that room, with silencer boxes.

I was thinking about getting a garage door that had a decent STC.

Forget STC. It's a lousy rating system that has no place in studios. Here's the actual definition of what STC is designed for, taken from ASTM E413, the document that defines the STC standard:

“These single-number ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling alleys, power transformers, musical instruments, many music systems and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands.”

STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio.

Do not use STC ratings to compare studio isolation products or techniques, for the very reason stated there by the inventors of the STC rating system.

I wasn't going to force/expect the contractor to achieve a high STC rating on the outside walls - he mentioned that he didn't have too much experience with it, and that makes me think it would be bad or expensive for me to get him and his team to try things they don't normally do, like exterior gypsum sheathing.

There seems to be a fundamental misunderstanding here. Isolating a studio is NOT accomplished by just trying to "achieve a high STC rating on the outside walls". Not is it accomplished by trying to achieve a high STC rating on the inside walls! Rather, it is accomplished by designing both the outside walls and also the inside walls as a system that act together to provide the isolation. The STC rating of each individual wall or "leaf" is irrelevant and meaningless, since they do not act individually. They act together as a tuned resonant system. The "room-in-a-room" system only works when it is designed to resonate at the correct frequency for the application.

Is there even a point in shooting for a very high STC on the walls of the room-in-a-room structure if I'm going to have conduit and ducts and a door?

Yes and no! You are correct that cutting holes in your isolation walls will obviously trash the isolation, but there are ways for dealing with that. You need to make "silencer boxes" (also sometimes called "baffle boxes") for those penetrations where a duct passes through a wall. Silencer boxes allow air to flow through while preventing sound from getting through.

The same applies for conduit: there are methods for isolating and decoupling the conduit where it passes across the cavity between leaves.

For doors, you don't just have one door: every door way has two doors, back to back. One goes in the outer leaf, the other goes in the inner leaf.

Won't the ducts and conduit through the walls ... have a maximum STC in the 30-40 range?

No. The level of isolation can be much higher when the silencers are designed and built correctly. I regularly get levels of 50 dB (and more) in well-built studios: Note that I said "50 dB", not "STC-50"! Those are two very different things. 50 dB of isolation is much better than STC-50.

I was thinking about trying out 1 layer of air-sealed drywall

I'm not sure what you mean by "air-sealed drywall". Please explain.

Do I need to give the contractor any special instructions for the room-in-a-room drywall install?

Oh yes! Very much so! First, make sure he reads and fully understands the book "Home Recording Studio: Build it Like the Pros", by Rod Gervais. Don't let him build anything at all for your studio until he has done that. Building a studio is very different from building a normal house.

Apparently some garage doors do have a decent STC ... Correct me if I'm wrong - that (STC 27) would about match an exterior gypsum and OSB sheathing layer.

STC-27 is pretty lousy! Not good at all. Even normal speech would be clearly audible through that. It's good as garage doors go, yes, but very lousy for studio isolation. Right now I'm working on a studio design for one of my customers who will be building his studio in his garage, with a situation similar to yours. In order to get decent isolation, we will completely lock the garage door into a fixed position (fully closed), seal it completely, remove the mechanism, motor, rails, etc., then build a single-leaf wall behind it to provide the actual isolation: That's the only way to do it. You cannot reply on the door itself for any usable level of isolation.


- Stuart -

I attached a picture of what I made in sketchup today for disambiguation.

The idea is the outside structure will have decent STC on its own (20-30), and the inside structure will shoot for a total STC of 45-50 from the outside. I realize that many STC ratings can be deceptive, especially with the bass-heaviness of my primary targets for isolation (lawnmowers), and my secondary targets (loud electric bass and drums). Additionally, I realize that you can't just slap products with stc ratings together and get additive benefits - I'm trying to follow the fairly common "two leaf" idea of two fairly heavy leaves that are as decoupled as possible, and have a reasonable air gap between them. Leaf 1: garage sheathing (and door), Leaf 2: inner wall of inside room.

The main design decision that I need to make is this - should I invest in getting the exterior wall to be as soundproofed as reasonably possible with a functioning garage door to further dampen noise before/after the main inner room wall, or would the outside area, at best, cost the same as getting the inner room beefier on its own and, at worst, provide a scenario for weird reverberations from the walls interacting with each other. It sounds like your verdict is that the garage door will be garbage, so I should just focus on the inner room (that was my original plan, but it seemed tempting to make the outside strong for redundancy and bonus mass for no floor space cost). My only worry for just focusing on the inside is the floor space cost for bumping the inner room out far enough to allow drywall to be installed on both sides...

Thanks for the real-world feedback on the baffling boxes from the gervais book. I assumed they were good, but I didn't expect they'd be that good.

air-sealed drywall - drywall installed with acoustic caulk (and whatever else) to prevent air from leaking through gaps at joints and such.

The idea is the outside structure will have decent STC on its own (20-30)...

I think you are not understanding at all what I am trying to tell you, so let me try again:

STC IS A TERRIBLE SYSTEM FOR MEASURING STUDIO ISOLATION: IT DOES NOT CONSIDER THE BOTTOM TWO AND A HALF OCTAVES OF THE MUSICAL SPECTRUM. IT DOES NOT CONSIDER THE TOP TWO AND A HALF OCTAVES OF THE MUSICAL SPECTRUM: IT CANNOT BE USED TO TALK ABOUT STUDIO ISOLATION. THE DEFINITION INCLUDED IN THE ASTM STANDARD ITSELF CLEARLY STATES THIS FACT.

I don't know how to make it any more clear than that. STC is no use at all for talking about studio isolation.

The idea is the outside structure will have decent STC on its own (20-30), and the inside structure will shoot for a total STC of 45-50 from the outside.

Even if STC was a useful system for talking about studio isolation, it still does not work the way you are suggesting. You CANNOT add STC values, or even decibel isolation values. Two walls that are rated at STC-20 and STC-30 do NOT give you STC-50 when you put them next to each other: You would probably get about STC-35.

I realize that many STC ratings can be deceptive,

No. Wrong. It is NOT that STC ratings are deceptive; It is that they simply are not applicable to studios. The definition written by the committee that created the STC system says exactly that: it is NOT an appropriate system for measuring isolation related to music. They did not say that it can be "deceptive". They said it should not be used AT ALL for that purpose.

I don't understand why you insist on using a system that is not suitable.

especially with the bass-heaviness of my primary targets for isolation (lawnmowers)

Lawnmowers are not "bass heavy". Most of their acoustic energy is in the lower mid and mid range, between about 100Hz and 2 kHz, peaking at about 500 Hz. There is very little energy output in low frequencies from a lawnmower:
You can clearly see that in the above graph: There's practically nothing in the very low end. No "heavy bass" in lawnmowers!

Additionally, I realize that you can't just slap products with stc ratings together and get additive benefits

Right. In fact, it is often the case that putting two such systems next to each other can REDUCE the total isolation (make it smaller, less isolation), compared to what each system isolates by itself.

I'm trying to follow the fairly common "two leaf" idea of two fairly heavy leaves that are as decoupled as possible, and have a reasonable air gap between them.

Except that you are not doing it correctly! Here's the equation that you need to use to do that:
That's the standard equation for calculating the resonant frequency of a fully decoupled two-leaf wall. It tells you what frequency the wall will resonate at, which is the frequency where it provides the WORST isolation. Once you calculate that, you then need these equations to calculate the actual level of isolation that you will get at different parts of the audio spectrum:
This is not complicated. It is simple high-school math.

And as you will notice, the equations have nothing at all to do with STC. Nada. Zip. Zilch. No relationship at all. They tell you what the isolation will be IN DECIBELS, not in worthless, useless, pointless, meaningless "STC" numbers.

Leaf 1: garage sheathing (and door),

Those are two different systems, with different characteristics. You cannot calculate them together. You have to calculate each individually.

Leaf 1: garage sheathing (and door), Leaf 2: inner wall of inside room.

You cannot sum the two isolation levels. Not in STC, and not in Decibels. It does not work like that. Decibels are logarithmic, so adding them is the same as multiplying the sound intensities, which is clearly silly. Even if you could add the numbers simply, you still could not get to a meaningful answer by doing that, since there are many other factors involved that all need to be taken into account.

You are assuming that it is a very simple thing to look at two different products and determine what isolation they will produce when you put them together: it is not simple.

should I invest in getting the exterior wall to be as soundproofed as reasonably possible with a functioning garage door to further dampen noise before/after the main inner room wall, or would the outside area, at best, cost the same as getting the inner room beefier on its own

The answer is: "invalid". You are not asking a valid question, because isolation does not work the way you think it does.

The TOTAL isolation of a wall is absolutely not related to the isolation provided by each of its parts. Period.

Here's a simple example:

The density of drywall is roughly 650 kg/m3, so therefore a single sheet of 1/2" thick drywall has a surface density of about 8 kg/m2. According to empirical mass law, the transmission loss (isolation) provided by that single sheet will be:

TL = 14.5 log (Ms * 0.205) + 23 dB
TL = 14.5 log (8 * 0.205) + 23 dB
TL = 14.5 log (1.64) + 23 dB
TL = 14.5 (0.214843) + 23 dB
TL = 26.11 dB

In other words, a single sheet of 1/2" drywall will give you about 26 dB of isolation.

According to your theory, if you have two of those next to each other, then you would get a total of 26+26 = 54 dB. Wrong! In actual fact, you will get a total of 30 dB. You don't add them at all: rather, you take the total combined mass for both sheets, and do the same equation. (If you had three sheets of that same drywall next to each other, the total isolation would be about 33 dB.)

That's for a single-leaf wall, where Mass Law is applicable.

If instead of putting your two sheets of drywall next to each other, you nailed one sheet to each side of a 2x4 frame, then that changes things. Now you have a coupled 2-leaf system, and the total isolation would be around 31 dB. HOWEVER! This is now a tuned system! There are resonances going on, and they REDUCE the isolation at some frequencies. In fact, this wall would be pretty bad at isolating all frequencies below about 125 Hz. And surprisingly, the isolation at low frequencies would be much worse than the isolation of just a single sheet of drywall at that frequency!

That's what you are missing here: the MSM resonance changes the entire system. It is no longer just the sum of its parts: it is something different now.

and, at worst, provide a scenario for weird reverberations from the walls interacting with each other.

It's not a case of "at worst". It's a case of "always". Any time you have two sheets of mass separated by an air gap, you will ALWAYS have resonance going on. It's just a fact of life. It WILL happen, not just in the "worst case". Its not "reverberation" either: it is resonance, which is not the same. And it isn't "weird" either: it is logical, predictable, and can be calculated very simply.

It sounds like your verdict is that the garage door will be garbage, so I should just focus on the inner room

No. You completely misunderstood what I was saying, and also misunderstood the concept of fully decoupled two-leaf MSM systems.

From what you say here, you seem to think that if one leaf is garbage and provides no isolation, then you can simply beef up the other leaf and still get good isolation. Wrong. It does not work like that, because the leaves do not act individually! They act together as a TUNED SYSTEM. If one leaf is garbage in a tuned system, then the entire system is garbage! It does not matter much what you do to the other leaf: it wont make a lot of difference at all.

Let me illustrate: If your body temperature is dropping because you happen to be standing in up to your waist in an large puddle if freezing cold water, you are saying that you can fix that and get your average body temperature back to normal by setting your head on fire! After all, if the problem is just about averages, then your frying brains will cancel out your freezing legs, and all will be well: your average body temperature is now normal....

While that would work fine if we were talking about a piece if steel with one end in a flame and the other in ice, it clearly and obviously cannot work for an entire human, since humans are systems! We are a lot more complex than a simple bar of steel.

The same with decoupled MSM walls: they are a SYSTEM, not a set of individual parts. It is the entire system that provides the isolation, not the individual parts. If one part is bad, then the entire system is bad, regardless of how good the remaining parts are.

If your garage door is lousy, thin, low-mass, unsealed, and porous, then it does not matter what you do to the other leaf: you will never get good isolation until you first take care of the garage door problem.

In other words, first step out of the icy puddle, then you wont need to set your head on fire!

(that was my original plan, but it seemed tempting to make the outside strong for redundancy

That would not work either, for the same reason. It isn't about having two separate leaves where one is "backup" for the other: it is about having a resonant system that consists of BOTH leaves, plus the air trapped between them, plus the acoustic damping in the cavity. They all work together as one single system, not just as a bunch of individual parts.

My only worry for just focusing on the inside is the floor space cost for bumping the inner room out far enough to allow drywall to be installed on both sides...

Once again, you are entirely missing the concept here: You do NOT put drywall on BOTH sides of your inner-leaf frame. You put drywall on only ONE side of that frame: That is the inner leaf. The other leaf is the siding on the outside of the other frame. So you have two frames, and each of those frames has sheathing on only ONE side. If you have sheathing on BOTH sides of your inner-leaf frame, then you have a three leaf system, which is even worse as it has multiple resonances, and the equation is more complex:

air-sealed drywall - drywall installed with acoustic caulk (and whatever else) to prevent air from leaking through gaps at joints and such.

There's nothing special about that: that's the normal, standard, ordinary, and required way of building any leaf. It MUST be sealed. If it isn't sealed, then isolation will be lousy.


- Stuart -

disambiguation of question: would if be worth trying to make a two-leaf system whose outer leaf would be bottlenecked by a garage door, or should I settle for a *one*-leaf system on the inside (and figure out how not to lose too much floorspace getting drywall on both sides of the inner room)? Further disambiguation of the garage door situation: the structure will not be allowed unless it is a garage and could be reasonably used as such (i.e. there's not a giant wall blocking the door )

You *really* hate the term STC. In the future, I will try to use transmission loss tables instead. I just thought that saying STC on a forum like this had the implicit caveat of "without an unacceptable drop in low frequency TL".

You pulled that lawnmower graph from the same resource I skimmed to find that a lawnmower had a fairly high peak (75dB) at 200Hz, but I guess that's still "low-mid" as you say. The paper mentions peaks at 100 and 125, but those aren't on any of the graphs. Maybe I'll break out the reference mic and do some science on my lawnmower!

Thanks for the isolation math, but I feel like you put a lot of words in my mouth to make me sound stupid. That is not appropriate etiquette on a forum.

According to your theory, if you have two of those next to each other, then you would get a total of 26+26 = 54 dB. Wrong!

I don't recall theorizing that.

would if be worth trying to make a two-leaf system whose outer leaf would be bottlenecked by a garage door, or should I settle for a *one*-leaf system on the inside (and figure out how not to lose too much floorspace getting drywall on both sides of the inner room)?

Sigh! One more time: For studio isolation walls, you do not ever put "drywall on both sides of the inner room". Never. Not ever. Not at all. Studio walls are TWO-LEAF systems. The inner-room is a SINGLE LEAF. It is a frame with drywall on ONLY ONE SIDE. If you put drywall on both sides of the inner-leaf, then you will have a 3-leaf system, where the isolation is WORSE than for the equivalent 2-leaf system.

the structure will not be allowed unless it is a garage and could be reasonably used as such (i.e. there's not a giant wall blocking the door

If that is, indeed, a building code requirement, then the answer is simple: you cannot have high isolation like that. Or rather you can, but you would have to do it with single-leaf construction, which would have to be very massive. Forget timber framing with drywall, and just build your inner-leaf from concrete block. That would be your only other option.

You *really* hate the term STC. In the future,

I don't hate it, no. I just use it where it is appropriate. And as the ASTM STC standard itself specifies, it is not appropriate for what you are trying to use it for. That's what I hate: using the wrong measure for the wrong thing, even after the reasoning has been clearly explained.

had a fairly high peak (75dB) at 200Hz, but I guess that's still "low-mid" as you say.

The frequency scale is logarithmic, because that's how our ears work. Half of the scale covers a region of 980 Hz between 20 Hz and 1000 Hz, the other half covers a region of 19,000 Hz, between 1,000 Hz and 20,000 Hz. Most acousticians consider "lows" to be 20 Hz - 200 Hz, "mids" to be 200 Hz - 2000 Hz, and "highs" to be 2000 Hz - 20000 Hz.

The paper mentions peaks at 100 and 125

A five-string bass goes down a bit below 31 Hz, two full octaves below those peaks. Kick drums normally have fundamentals around 50-80 Hz, an octave below those peaks. Keyboards go down even lower, about three octaves below those peaks. Those are "low" frequencies.

Thanks for the isolation math, but I feel like you put a lot of words in my mouth to make me sound stupid. That is not appropriate etiquette on a forum.

If you don't like the way I responded, talk to the moderators. The terms of service of the forum are stated on the page where you signed up to join.

If you are not using that math to calculate your isolation, then you have a problem: It is the only math out there that works for calculating isolation! There are more complex versions, that take into account more aspects to give more accurate answers, but the simple versions of the equations that I posted are plenty accurate enough for typical home-studio design. I usually use only the simple versions, even when I'm designing high-end professional studios, because the small amount of additional accuracy that I could get form the complex versions simply isn't relevant for most studios, and the actual construction materials and techniques are not perfect in any case: prediction does not usually match reality with extreme accuracy, so I don't see a need to use excessively complex equations when the simple ones are sufficiently accurate. But I DO see the need to actually do the calculations! It's the only way to be certain that the proposed structure, materials, methods, and techniques will actually produce a studio that isolates correctly, and works well acoustically.

There's one basic piece of information that you haven't mentioned yet: How much isolation do you need? (In decibels).

That's the most basic, fundamental starting point for any studio design. It would help if you could define that first. It's the only sure way to guide you to the optimal wall design. It's one things to need a studio that isolates to 40 dB (even a house wall can do that, if you beef it up properly), and entirely another thing to need a studio that isolates to 80 dB (well beyond the possibilities for practically all home studios).

- Stuart -

Just wish you good luck for your studio. Hope that you will build it soon. Even you can consult an architecture so that according to your style and what you are thinking will suggest you good things. While doing these major things like home design, you also focus on small thing like a proper electrical outlet, sewer outlet etc.

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