Experimental Plan for absorption

[grega60438]

Recording space: 24'Lx16W' with 8'H ceilings; concrete floor:
The room is partially anechoic, with about 8" cellulose insulation covering two-thirds of the walls and ceiling. Rubber on the floor. I added reverb to create the space I wanted, using the TC Electronic Powercore MD3 and VSS3.

I am tearing out all the cellulose insulation, to add more layers of drywall.
Now is my chance to try some experimentation. I want to try a more live recording area. If I don't like it, I can always add more absorption and go back to anechoic.


The Experimental Plan:
ALL horizontal ceiling corners covered with 12"x12"x17"cellulose insulation (House wrap covered)(Two are 24'and two are 16' long)

ALL vertical wall corners covered with 12"x12"x17"cellulose insulation (House wrap covered). (Four 8' high)

Eventually will also additional panels to the walls and ceiling. We can cross that bridge later.

Questions:
Any reason to add 703/705/FRK/alternative surface, to the hypotenuse (17")?

I am still learning, so forgive me if I am off with my assumptions. Is this right?
12" of cellulose is excellent for absorbing the low frequencies in the corners.
703/705 on the hypotenuse will significantly lower the frequency of the bass trap.
FRK reflects higher frequencies. Could be a good thing?
705 has a higher density than the 703.
The 705 with FRK will reflect more higher frequencies, while at the same time create a lower frequency trap.
The 703 has less density, will be similar, but what is the change? Higher frequency bass trap? More high&mid frequencies absorbed?


Thanks,
Grega60438

[Soundman2020]

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

Recording space: 24'Lx16W' with 8'H ceilings; concrete floor:

So it is a perfect modal resonant chamber, tuned to 70.6 Hz, with major, huge, extreme modal issues? Why did you choose those dimensions? It's about as bad as it can be. Width is exactly twice the height, and length is exactly three times the height. You have created the perfect acoustic storm!

The room is partially anechoic, with about 8" cellulose insulation covering two-thirds of the walls and ceiling.

Well, actually, that's a long way from anechoic. 8" of porous absorber on the walls is not going to make a room anechoic. It will make it dull, for sure, and rather odd sounding, certainly, but not anechoic. It will kill pretty most of the low-mids and mids, massacre any hope of a diffuse field, murder and bury all the high-end liveness, yet leave the low end alone.

rubber on the floor.

I thought you said the floor was concrete? So which is it? Concrete, or rubber? There's a HUGE difference, acoustically.

I added reverb to create the space I wanted, using the TC Electronic Powercore MD3 and VSS3.

I'm not sure I understand: You have a room that is fairly large, and with some modifications could make a decent tracking room with nice acoustics, then you killed it completely with absorption, and add reverb in the mix to try to get some life back? I guess I'm not seeing the big picture here: what is the purpose of the room?

I am tearing out all the cellulose insulation, to add more layers of drywall.

Why? For what purpose do you want to add more drywall? What are you hoping to achieve by that?

While you are ripping things out, rip out the rubber flooring too, and just leave the bare concrete. That would be a major improvement, just like that.

The Experimental Plan:
ALL horizontal ceiling corners covered with 12"x12"x17"cellulose insulation (House wrap covered)(Two are 24'and two are 16' long)
ALL vertical wall corners covered with 12"x12"x17"cellulose insulation (House wrap covered). (Four 8' high)

Once again, the big question is WHY? What are you hoping to achieve with that? What is the purpose of the room? Why do you want to go from a muddy, boomy, dull room to a heavily bass trapped room with major flutter echo issues?

I'm really not understanding the point of your experiment.

And why experiment at all? It's MUCH better to just design the treatment correctly to do the job you want done. There's no need for experimenting: te science of acoustics is very well advanced, and it's fairly simple to design treatment and predict the outcome, then tweak it as needed. Here's an example of how that is done in the real world: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=21368

Any reason to add 703/705/FRK/alternative surface, to the hypotenuse (17")?

For what purpose? To answer that, we would need to know the acoustic properties of the specific type of "cellulose insulation" you plan on using, and the type and thickness of the "house wrap" that you plan in using, plus the way you plan to use it: there's a difference between leaving it loos and stretching it taught, as well as a difference between full coverage and partial coverage. There will certainly be a difference if you add either 703 (with or without FRK) or 705 (with or without FRK), but without knowing WHAT you are trying to achieve, it's hard to say if that would do the job of not. You seem to want to build rather small superchunks in all your room corners, but you don't explain why, then you want to add house-warp over that, but don't explain why you chose housewrap (which is porous and therefore not a good membrane) instead of the more common HF reflection options. Then you mention adding 703 FRK or 705 FRK (two very different products, for different purposes), so it seems you want to both reflect and also absorb mids... that doesn't make a lot of sense.

Please explain, first of all, what the purpose of this room is: Live room? Tracking room? Rehearsal room? Control room? Mastering room? If it is live, tracking, or rehearsal, what genres? What instruments?

12" of cellulose is excellent for absorbing the low frequencies in the corners.

Not very much. Superchunks are commonly 36" along the edges, or sometimes cut down to 24" if space is a problem. Less that that isn't a lot of use. You are going to have huge, major, enormous modal issues in that room, due to the perfectly related dimensions, so you will need MAJOR bass trapping, with peak absorption at 70 Hz, 100 Hz, 117 Hz, 140 Hz, and many others, where
several modal frequencies coincide exactly, right on top of each other. You also have the fundamental modal issues at 23.5, 35.3, and 42.4 Hz, which are going to be big as well. You need huge amounts of bass trapping in there, if this is a control room, and very extensive bass trapping even if it is a live room.

You also mention "cellulose insulation", but with no details: there are numerous types of cellulose insulation, all of which have vastly differing acoustic properties. Without knowing which specific one you are talking about, there's no way of knowing what it will do. And without knowing what you WANT to do in that room, even if we did know what the properties are, we still couldn't tell you if the cellulose would be any good for you!

703/705 on the hypotenuse will significantly lower the frequency of the bass trap.

No it wont. It will have an effect, yes, but 705 is too heavy to be good for bass. 701 would be better. What frequency do you want it to work at? You mentioned doing corners only, so clearly you are after modal issues. Is that it? Or are you trying to achieve somthing else?

Unless you tell us what your goal is, we can't help you get there...

FRK reflects higher frequencies. Could be a good thing?

It can be, yes. In the design for the corner control room ceiling cloud (read the thread I linked you to above) I am using 703 FRK as part of the system, to prevent the 703 from over-absorbing the highs. But I designed it as a SYSTEM: I didn't guess. First I measured the actual, real acoustic response of the room, analyzed it to see what needed doing, then did the math with a few different options, and came up with the 703FRK as being the best... for that specific case!

705 has a higher density than the 703.

Yes. Which makes it WORSE for bass trapping, not better. You seem to be under the common misunderstanding that higher density is better for bass: wrong. Lower density is better for bass.

The 705 with FRK will reflect more higher frequencies, while at the same time create a lower frequency trap.

No. 705 is not as good as 703 or 701 for bass, and the FRK actually extends down into the mid range with reflectivity. Your plan is not going to work the way you are hoping it will work.

The 703 has less density, will be similar, but what is the change? Higher frequency bass trap? More high&mid frequencies absorbed?

Change relative to what? You are starting out with a false premise, and insufficient data.

Here's what you need to do, in order:

1) Define the purpose of your room. What do you plan to do in there?
2) Define your isolation. How much isolation do you need, in decibels, to the outside world
3) Define the basic room acoustic signature: What do you want the room to sound like? If it is a control room, then it MUST sound exactly like ITU BS-1116.3 says it should. If it is a live room, then it must sound "live", correctly tuned for the instruments and genre. Etc.
4) If the room signature cannot be achieve with those very, very problematic dimensions, then modify the shape as needed.
5) If you are not getting enough isolation, then modify the room to be a true fully-decoupled 2-leaf MSM room-in-a-room system, in order to get the isolation you need.
6) Build the room to the final size/shape that will give you the acoustic signature that you need.
7) Measure the actual acoustic response of the empty room, and compare that against the predicted response.
Decide what initial treatment you will need to deal with the largest issues in the room: design it following the usual procedures and calcualtions, install it, then measure the response again to see if it is working OK.
9) If it is not working, modify it and try again.
10) Once the initial treatment is working, analyze the acoustic measurements again, to see what the next biggest remaining issues are, and treat those.
11) Repeat steps 8, 9 and 10 until the room is behaving exactly the way you want it to behave.

That's the normal procedure for treating a room. Guessing and experimenting is not a good way of getting there. Just follow the process, do the math, and you'll get what you want. No experimenting needed.

(And don't forget to check the forum rules!)


- Stuart -

[grega60438]

First let me say I appreciate your willingness to help teach me, and I will try hard to get myself in line and be teachable
Missing a few things: My apologies, I have updated my profile. I am from the Chicago suburb of South Holland IL. USA.

History and goals:
I have mixed music at church for about two decades. I also did live music for about a decade, but my back could not handle carrying all the equipment (two back surgeries), so I switched to the goal of a recording studio. My goal is to help bands that can't afford much, from recording all the way to mastering. I want to do charity for church bands, and poor people to crate demos. I know electronics, and IMHO know how to mix and OK for mastering, but the sound treatment is not my strong suit and I am requesting help.

The space is a garage 24'x24', which my wife said I could have for the above goal. I sectioned off 5.5'x24', where I and the band members are at while recording. The actual recording occurs in the 24'x16' space. The dimensions don't add up perfectly as there are double 2x4 walls separated by 1" gap on the outside walls. The sectioned off 5.5'x24' space also has a double door airlock space to the outside world. No windows anywhere.

Q: Define the purpose of your room. What do you plan to do in there?
A: Record bands in the larger space 24'x16'.
Mix and eventually master in the same larger space after the band departs. This is for charity demos. Unfortunately the recording area is 16'x 24' ish.

Q: Define your isolation. How much isolation do you need, in decibels, to the outside world
A: As much as possible, that is affordable, and is value added for charity. Does 50dB sound reasonable for road noise? The road behind my recording studio, is about 30' away, with traffic noise. Not trying to keep studio noise in, but I am trying to keep traffic noise out. I can hear the traffic on sensitive condenser microphones, about -50db down. This has me concerned. I already have double 2x4 walls separated by 1" gap. The outside wall has only one layer of 1/2" OSB. On the inside walls, I am planning on increasing the existing one layer to six layers of 5/8" drywall. I have already purchased enough drywall and green glue to do six layers total of 5/8" drywall.

Q:So it is a perfect modal resonant chamber, tuned to 70.6 Hz, with major, huge, extreme modal issues? Why did you choose those dimensions? It's about as bad as it can be. Width is exactly twice the height, and length is exactly three times the height. You have created the perfect acoustic storm!
A: Charity is what I have, and the space is what I have. What can I do to improve? I can completely remove the dry wall ceiling, and gain about 4 more foot height peak of a trapezoidal roof. Peaked at the center and angled out. Should I remove the ceiling and raise to the roof rafters? I will if it makes a difference. Or is the space not useable?
It appears I should solve this before anything else. I am not trying to make money. I am willing to do whatever it takes to help others, but I am not rich enough for a new space. I want to make a difference and help others in this life, if I can. I thank you for trying to help me...

[Gregwor]

My apologies, I have updated my profile.

Thank you sir!

but the sound treatment is not my strong suit and I am requesting help.

This forum is a great resource, but realize that it is not a one on one free tutoring service or course. The forum exists to answer questions that have not been answered on here before, and to have more experienced members look over your plans and make suggestions to improve your design. More than anything, contributing members will speak up to stop you from making major mistakes that will cost you time and money!

I sectioned off 5.5'x24', where I and the band members are at while recording.

You lost me here. So right now you all cram into a 24' long hallway and record live off the floor?

The actual recording occurs in the 24'x16' space.

But an actual recording happens in a larger space off of the hallway? See why I'm confused?

The dimensions don't add up perfectly as there are double 2x4 walls separated by 1" gap on the outside walls.

So you have an "outside wall" (your outer leaf that later on you describe as having 1/2" OSB sheathing on it.
Then you have two more 2x4 walls that are separated by a 1" gap. Let me illustrate what you've described:

1/2" OSB mounted to some exterior wall frame (assuming a commonly used 2x6 frame) --> air gap of unknown amount --> 2x4 frame with nothing mounted to either side of it --> 1" air gap --> 2x4 frame with 1 layer of 5/8" drywall mounted to it

If I have this right, why have the extra 2x4 frame in between your "exterior wall" and the "interior wall"?

You also never told us about your ceiling. Is it fully decoupled and only sitting on your "interior wall" (by the way, we call that the inner leaf here)?

You really should draw this entire thing up in SketchUp Make so we have a better picture of what is going on.

The sectioned off 5.5'x24' space also has a double door airlock space to the outside world. No windows anywhere.

So, you what I'm understanding here is that you have your outer leaf (you call it exterior wall), then a 2x4 frame around the whole thing. THEN you have your big space fully decoupled, THEN you also have a 5'6" hallway that is 24' long that is also fully decoupled?

As much as possible, that is affordable, and is value added for charity.

What is affordable to you? Some musicians I know see $20 as affordable (actually). Donald Trump sees 1 billion as affordable. I know that's an extreme comparison, but if your budget is only $1000 with that size of room, we have a problem.

I don't understand what you mean by "is value added for charity". Please elaborate. Are you trying to say that you want your charity recordings to sound better by having more isolation from the road noise?

Does 50dB sound reasonable for road noise? The road behind my recording studio, is about 30' away, with traffic noise. Not trying to keep studio noise in, but I am trying to keep traffic noise out. I can hear the traffic on sensitive condenser microphones, about -50db down. This has me concerned.

Achieving a total isolation value of 50dB is pretty standard and doable using the recommended techniques found on this forum and used by most of the members who have built successful spaces. Isolation is a two way street. If you want to keep 50dB of noise out, then you also will keep 50dB of noise in.

I already have double 2x4 walls separated by 1" gap. The outside wall has only one layer of 1/2" OSB. On the inside walls, I am planning on increasing the existing one layer to six layers of 5/8" drywall. I have already purchased enough drywall and green glue to do six layers total of 5/8" drywall.

I still can't wrap my head around why you have two 2x4 walls inside of your outer leaf. Anyway, moving past that fact, I will address your isolation game plan. I can quite confidently say that it won't work as well as you hope it will. Here are some points to explain why:

1. Even if you did want to attach 6 layers of drywall to your inner leaf, that is a LOT of weight that you probably didn't know that you'd be attaching to your ceiling joists when you initially build your ceiling structure. Chances are, with your 16 foot span, your current joists won't handle that extra weight. You would have to check with your structural engineer to see if in fact it can hold that weight or how you can go about strengthening it.

2. The most important factor here is that, assuming your inner leaf is in fact fully de-coupled as it should be, you will be trying to increase your transmission loss by manipulating one of the two main design factors of the Mass Spring Mass equation. This equation works under the assumption that both mass variables are close in value to one another. A typical home studio build would consist of two layers of drywall on the outer leaf, a gap filled with insulation (this is the "spring" part of the equation), then a the inner leaf that consists of another two layers of drywall. This will work amazing. Pretty much adding the effectiveness of two single walls together! HOWEVER, what your proposed plan is, is having a thin and light single piece of 1/2" OSB on your outer leaf, then a massive SIX layers of drywall on your inner leaf. Here is a perfect example of why yours won't work properly: With an exaggerated comparison to your design, let's say the outer leaf has a single piece of paper on it. Very thin and light, of course. Then the innerr leaf was a concrete wall. Sure, there would be an air gap filled with insulation between the two. Think about it: do you really think that piece of paper is doing anything measurable? I'm confident that you could remove that piece of paper and you wouldn't notice a difference. HOWEVER ,if you were able to have half the amount of concrete on the inner leaf, have the same air gap, then put that same amount of concrete on the outer leaf (so now both leaves had the same amount of concrete), it would perform amazingly!

Your proposed design would damned near perform as well as a single wall with 6 layers of drywall on it. The 1/2" OSB would BARELY improve the performance of the wall.

Your best bet would be to rip off the existing 5/8" drywall and use that material to beef up your outer leaf. If I were you, I would probably add two layers of 5/8" drywall to your outer leaf. Then use 2 or 3 layers of drywall on your inner leaf (you said you already own this drywall right?)

What can I do to improve? I can completely remove the dry wall ceiling, and gain about 4 more foot height peak of a trapezoidal roof. Peaked at the center and angled out. Should I remove the ceiling and raise to the roof rafters? I will if it makes a difference. Or is the space not useable?

If you have usable space above, and you are able to build a proper inner leaf ceiling structure within that space, then yes, yes, yes.

You didn't mention what you have for HVAC right now. If you want to maintain the isolation you'll achieve by properly building your shell, then there's a good chance you'll need some or all of that space above your room to run duct work and mount massive silencer boxes.

It appears I should solve this before anything else. I am not trying to make money. I am willing to do whatever it takes to help others, but I am not rich enough for a new space. I want to make a difference and help others in this life, if I can. I thank you for trying to help me...

Yep, if you want this place to work better than it currently does, now is the time to address your isolation issue. However, before you do that, you need a plan of attack. That includes sorting out HVAC, electrical, plumbing (this is needed for your HVAC), etc. So, 3D model the place as accurately as you can (literally draw every stud and rafter). Design the place 100%, THEN get building permits, engineers stamps and start building.

Before you do any of this, I can't stress enough how important it is for you to study and learn about acoustics before you start getting discouraged and feel lost by reading endless hours on this forum. You should read this:
www.roletech.net/books/HandbookAcoustics.pdf
THEN use the search function on this forum to look up things like:
HVAC silencer box
Inside Out
4731
Soffit mounting
Garage Door
REW
Soffit Wings

After you study that stuff, chances are, you'll be off to the races. I look forward to your progress as your vision and situation sounds pretty awesome! I hope this was helpful and know that contributing members ARE here to help, answer questions, and like my reply here today, teaches you, albeit indirectly.

Greg

[Soundman2020]

Missing a few things: My apologies, I have updated my profile. I am from the Chicago suburb of South Holland IL. USA.

Excellent! That's what was missing.

My goal is to help bands that can't afford much, from recording all the way to mastering. I want to do charity for church bands, and poor people to crate demos.

That's an excellent and laudable goal. I'm a church man myself: I've been running live sound for churches since as far back as I can remember, all the way to early childhood, "helping" my dad twist the knobs and flip the switches on his ancient reel-to-reel deck, which served as the entire sound system. I also teach seminars to churches on how to do sound right. So I certainly understand where you are coming from: Been there, done that, still doing it. I have also recorded some albums pro-bono, or nearly so, and provided plenty of recording/mixing/mastering/acoustic tips for Christian musicians.

I feel for what you are trying to do, 100%.

However, even though my time is my own to give away for free, the equipment I use has a cost: The better quality it is, the more it costs. Tracking well, even for non-professional musicians who can't afford big-name pro studios, still has a cost. You can't do it with a US$ 5 mic that you picked up in a toy store! You can't use cheap a cheap, battered guitar with ten-year-old nylon strings! You can't use a practice electric guitar amp that you found on the junk heap! If you want to make quality recordings, you need quality gear. Then comes the mixing: You can't do it on the tiny little junk PC speakers that you found covered in dust ad bird droppings at a garage sale. You need quality speakers that have flat response across the spectrum you are dealing with. Even more so for mastering. You probably already understand all of the above, to a greater or lesser extent, and I'm sure (or at least hope!) that you have invested in the best possible mics you can find, and the best possible studio monitors you can find. If you don't at least have those two, then there's no chance of achieving what you want. But assuming that you do have those, that's still not enough.

The best mic in the world, placed in a room with lousy acoustics, will sound lousy. Even if you use it close-mic the instruments, it still won't sound the way it should. If the room is "boomy", then everything you record will have a hint of "boomy" in it, no matter how hard you try to EQ that. If the room is "harsh", then ditto: everything will sound harsh. If the room has a sizzling flutter echo in the high mids, then the mics will grab that too, and it will be in all your tracks, no matter how much you try to drown it with canned reverb, delays, or whatever. This is like making soup: if you put too much salt in at the start, it will be too salty always! Even if you add garlic and onions and carrots and whatever, there will always be that underlying sensation that it has too much salt, and there's nothing you can do to get rid of that. Therefore, the tracking room needs to have the right acoustic response that allows the instruments to sound good in the room, and on the mics. And just like you can't record a great vocal on a five dollar mic, so too you cannot get good acoustics on a five dollar budget. Even though your goal of providing a recording space very cheap for Christian musicians who have no money, is very admirable, and very laudable, there's still the basic fact that getting a room to sound good for tracking will cost you money, just as a closet full of great mics will cost you money, and a peair of great mastering speakers will cost you money.

And in the same manner, you already know that you'll never get a good instrument track if you don't know where to put the mics on the instrument and in the room: It takes a lot of study and practice and research to know just how to set up the mics on a drum kit, to capture a set of tracks that really sounds like a drum kit in the mix! You need to have a deep understanding of how condenser mics work, and ribbon mics, and dynamic mics, and boundary effect mics, and shotgun mics, what their polar patterns are, what their frequency response is like, when to use each one, when NOT to use each one, what instruments will work best with each mic type, where to put it, how to orient it, how to arrange several mics together to capture the full sound of the instrument, etc, etc. You already know this, I'm sure, so you know that it's not something you can figure out in a few minutes, or learn overnight, or get right from a couple of "experiments". Good mic placement comes from understanding instruments, and understanding mics, and understating music. It takes time to learn how to do it. You will never get good sounding tracks if you don't do the research and study to understand all of this

In the same way, you will never get good room acoustics if you don't do the research and study to understand how sound works, how treatment works, where to use what type of treatment, why, how, what goal can be achieved in what ways with various types of treatment, etc. You need to understand acoustics deeply, just as you understand mics and instruments deeply already.

The fact that you want to offer your services free, or at low cost, or charitably, is great, but is also irrelevant. There will be an unavoidable cost in materials and workmanship, just as there is an unavoidable cost in mics, speakers, amps, and instruments. The higher quality results you aim for, the higher the cost will be. You can't by a U47 for ten bucks, and you can't by great Fender or Gibson or Marshall for ten bucks, and you can't buy great isolation or great room treatment for ten bucks either! Many musicians and sound engineers make the mistake of thinking that the room doesn't matter: with a great guitar and a great mic, you can always get a great recording. Wrong. The room matter, and it matters greatly. In fact, I'd go so far as to say that in a great room, you can get very decent recordings with a not-so-great mic. Believe it or not, I've done some vary acceptable electric guitar recordings and even drum recordings, using nothing more than a few humble SM-58's, carefully placed in a a great room. But even the best setup with 414's and U47's on a drum kit in a lousy room, is going to be lousy.

That's my long and winding preamble that leads me to your solution: You need quality acoustics in your room to achieve what you want to achieve, regardless of your goal of charitable service, and you can't get quality acoustics without researching, studying, and paying the price that needs to be paid.

That might not sound like a very useful statement, but read it again a few times, and repeat it in your head, until you get it.

Stated another way: Christian churches are big on teaching charity, yes, but they are also big on teaching good stewardship. Use the gifts and talents that you have been given wisely. This might come across as harsh, but blindly buying up thousands of square feet of drywall and hundreds of cubic feet of unknown insulation, just so you can experiment with it, hoping it might do something, is not good stewardship. I'm glad you have the money to do that, because that amount of drywall and insulation doesn't come cheap, but to be very honest, it is all wasted money. You have bought stuff that won't do what you are hoping it will do, as Greg has already pointed out. And you have NOT bought the stuff that you WILL be needing in order to get to your goal.

I would strongly suggest that you should return that drywall and all the other building materials for a full refund, then put the money in the bank on fixed deposit (remember the Biblical account of they guys given 1 talent, 2 talents and 5 talents....), and leave it there until you have completed the research, study, and design of your studio, properly and completely. Then use that money to buy what you will ACTUALLY need to do the job.

I know electronics, and IMHO know how to mix and OK for mastering, but the sound treatment is not my strong suit and I am requesting help.

Great! Then you fully understand that everything I said above is true and correct. And you are in the right place for help. But as Greg mentioned, the forum is more like an "assisted self-help" place: you still need to do the basic groundwork yourself, come up with a plan for your studio that is based on the principles of acoustics, post it here, and we'll be more than happy to help you refine that plan, to make it workable. On the other hand, if you don't have the time or inclination to do the months of research that you will nee to do, and the months of design work that you will need to do, then you should consider hiring someone to do the design for you. Yes, it will cost you money, but probably not as much as you think. And it will save you time AND money in the long run. Plus, you'll end up with a great studio that does everything you need, where you will be able to offer your charitable recording/mixing/mastering services to the best of your ability.

I sectioned off 5.5'x24', where I and the band members are at while recording. The actual recording occurs in the 24'x16' space.

Just like Greg, I'm having trouble understanding that: Are you recording in both places at once? The long, narrow 24x5 space, and also the much larger 24x16 space? If you are only recording in the 24x16 space, then why are the musicians on the 24x5 space while the recording is going on? I don't get what you are trying to say here.

The dimensions don't add up perfectly as there are double 2x4 walls separated by 1" gap on the outside walls.

That doesn't make sense either. It appears that there's misunderstanding of how isolation works. If you have the outside walls of the garage itself, then " double 2x4 walls " within the garage, you have a three-leaf system which is not good for isolation. 3-leaf walls are lousy for low frequency isolation.

Please provide a detailed diagram if what you actually have there, and photos, so that we can better understand your situation, and help you fix it.

The sectioned off 5.5'x24' space also has a double door airlock space to the outside world. No windows anywhere.

Once again, that doesn't make a lot of sense, and is not the way sound locks are supposed to be built.

Q: Define the purpose of your room. What do you plan to do in there?
A: Record bands in the larger space 24'x16'.
Mix and eventually master in the same larger space after the band departs.

That's a problem A BIG problem! The acoustic response that you need for a live room, to successfully track instruments and vocals, is VERY different from the acoustics response that a room needs to mix well, which is also different from the acoustic response that a true mastering room needs. You have steeply conflicting requirements here: If the room is treated to make it a great place for tracking, it will be terrible for mixing, and even worse for mastering. If it is treated to be perfect for mastering, then it will also be good for mixing, but really, really bad for tracking.

There is a solution: variable acoustics. It is possible to build variable acoustic devices on the walls, that you an open, close, swing, rotate, slide, flip, or otherwise physically change in some way, to change the acoustic response of the room. When you set all of those devices to one configuration, the room will be fine for mixing, and when you set them to another configuration, it will be fine for tracking. Here's an example of such a device that I designed for one of my customers a few years ago:

Variable-acoustic-01--panels--construction--half-open-SML.jpg

Variable-acoustic-02--panels--construction--fully-open--SML-ENH.JPG

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You would need several devices around the room to be able to get enough change. The device above would not be suitable for what you need: that was designed specifically for a large isolation booth, to provide some variability for dealing with different instruments and vocals. Yours would be very different, but those photos illustrate the concept.

There are several other conflicting requirements for using one single room for both purposes, which you will also have to address in your design, but that's one of the big issues.

Q: Define your isolation. How much isolation do you need, in decibels, to the outside world
A: As much as possible, that is affordable, and is value added for charity. Does 50dB sound reasonable for road noise?

As Greg mentioned, 50 dB is achievable, and is a realistic goal. Take a look at the corner control room thread that I linked you to in my previous reply: he gets a bit over 50 dB. I originally designed his studio for 55 dB, but he wanted to have operable windows, and didn't mind taking a small hit on isolation for that. Even with those windows, he still gets over 50 dB.

However, road noise is a different issue: You should look into that carefully. Road noise has two components: airborne, and ground-borne. The airborne part is the noise that comes to you through the air, from the vehicles on the road to the walls and roof of your garage, then gets inside through those. Ground-borne is a different thing entirely: it is the low-frequency "rumble" that is transmitted through the ground itself, in the form of vibrations that travel through the ground, then into the structure of the studio. If you have a problem with ground-borne noise, that's a much more complex issue to solve. It is far more pervasive, because it causes the entire building to vibrate, and isolating that is not easy. It can be done, yes, but it's complicated. You can do a simple test to find out if you have that type of ground-borne, structure-borne sound: borrow a stethoscope and use that to listen the the concrete slab. Hopefully you have a friend who is a doctor or nurse, or maybe there's someone in the church congregations who is: ask them if they could lend you a good quality stethoscope, and use that (carefully! Don't damage it!) Place it directly on a clean, smooth section of the slab, when there is heavy traffic on the road outside, and see if you can hear the traffic "rumble" in the slab itself. Do the same on the studs, and n the joists. I'm really hoping that there is no discernible structure-borne sound! If there is, then I have sad news for you: you are going to need a lot more money to deal with that.

I can hear the traffic on sensitive condenser microphones, about -50db down. This has me concerned.

Yes. And rightfully so! That's the type of sound that you can't get out of the mix once it is in. "Salty soup" again. You can EQ to reduce it, but that changes the sound of the instrument or vocal. You can try to gate it, or put an expander on it, but that can produce "pumping" artifacts, and the sound will still be there, underlying the music. You can try to drown it with effects boxes, and that an work to a certain extent too, but it doesn't fix the actually PROBLEM: it merely disguises it.

On the inside walls, I am planning on increasing the existing one layer to six layers of 5/8" drywall.

As Greg already pointed out, that will not work. You might disagree, and think "How can these guys say that six layers of drywall will not isolate the room? They must be really dumb!" But the science is clear. For single-leaf walls (which yours basically is, as Greg explained), there is an equation called "Mass Law" that defines how much isolation you will get from mass alone. It's a very simple equation, and goes like this:

TL = 14.5 log M + 23 dB
Where: M = Surface Mass in lb/ft2

Do the math: A single sheet of drywall has a surface density of around 2 lb/ft2, so that will get you roughly (14.5 x log(2) +23) =27 dB of isolation. Six layers will get you (14.5 x log(2*6) +23) = 38 dB. So all your hard work, and huge investment, and large amount of lost space, will gain you about 10 decibels of isolation, and you will still be way short of your 50 dB goal. Mass law says that you would need about FIFTY layers of drywall to get that amount of isolation. Yup. Acoustics is not intuitive, and there are many surprising things that pop up, when you least expect them. Mass law is not just a mathematically interesting equation: it is a very good representation of what really happens in the real world.

Now, if you were to use only a third of that drywall, making a proper two-leaf wall that has two layers of drywall on each leaf, with Green Glue, and a decent air gap that is filled with good insulation, then you could, indeed, get 50 dB of isolation. Because two-leaf walls are not subject to mass law alone: they are also subject to the laws of resonance, which changes everything. Different ball-game entirely.

I have already purchased enough drywall and green glue to do six layers total of 5/8" drywall.

As I said before return that for a full refund while you can, save the money in the bank, earning interest for the many months that you will need to learn acoustics and do the complete design, then take some of that money out and use it to buy the materials that you will ACTUALLY need, to get the job done right.

Charity is what I have, and the space is what I have.

As I explained at the start of this post, in my long-winded, rambling, meanderings manner: charity is wonderful, and laudable, and excellent, but it won't get you what you need to do the job you want. The building materials and sound waves have no concept of "charity", and won't perform any different just because you are doing charitable tracking and charitable mixing: they will perform the same for you as for everyone else. Drywall won't block sound better because it admires you charitable efforts: it will still work just the same.

Regarding the space: Yes, it is what you have, but it can be modified. It is feasible to take down some or all of what you have already built, doing so carefully so you can recover the materials, then re-build it the correct way. So the space is what it is, yes, but it CAN be changed. This is not a matter of physical limitations, but rather a matter of willingness, embarrassment, and perhaps pride.

I can completely remove the dry wall ceiling, and gain about 4 more foot height peak of a trapezoidal roof.

That's a possibility yes, but only in combination with also removing the walls and starting again (assuming they have been built incorrectly, which seems to be the case).

Should I remove the ceiling and raise to the roof rafters? I will if it makes a difference. Or is the space not useable?

Perhaps the first law of small-room acoustics should be "maximize volume". Getting the greatest possible air volume in the room is one of the bet things you can do to improve the acoustics response of a small room. Especially if it is a tracking room. Having a higher ceiling in a tracking room is also a very, very good thing: the higher, the better. The only problem here would be how to deal with the issue of isolation: there are certainly joists up there that the current ceiling is nailed to, and those are likely part of the trusses that hold up the roof. You need to "get rid of" those joists so you can raise your inner-leaf ceiling, but you cannot do that if they are part of the trusses! But what COULD be done, is to modify your trusses to convert them into "raised tie" or "collar tie" trusses, where the joists are replaced by structural members further up each truss. That's is feasible, but requires the skills of a structural engineer to figure out where to put the new ties, and what size lumber to use, before taking out the joists. DO NOT TRY THIS ON YOUR OWN! Hire an engineer to do it. That would probably allow you to raise the inner-leaf ceiling by several inches, maybe even a couple of feet, best case. That is very worthwhile acoustically. I have done that for the studios of a few of my customers, and it woks. But ALWAYS with the consulting advice of a qualified structural engineer.

It appears I should solve this before anything else.

Maybe, but the ceiling is only PART of the issue. You need to stop thinking about your studio as a bunch of separate walls, frames, drywall, insulation, doors, etc., and start thinking about it as a complete tuned system. All of the parts work together in a totally different manner from the way each of them works by itself. Just fixing the ceiling will not do anything to fix the overall isolation, nor the overall acoustic response. It will help, yes, but it's only one part of the entire solution.

- Stuart -

[grega60438]

First I appreciate the attempts to help from SoundMan and Greg.
It is apparent I have much learning. I am in the process of reading HandbookAcoustics.pdf
You have helped point me in the right direction.

Thank you,
Grega60438

[Gregwor]

First I appreciate the attempts to help from SoundMan and Greg.
It is apparent I have much learning. I am in the process of reading HandbookAcoustics.pdf
You have helped point me in the right direction.

Our pleasure!

I look forward to hearing back from you after you read the PDF! It's an amazing read. My favourite part is in the diffraction chapter when the author talks about the experiment off the cost of Australia and how the sound travels so easily through the salt water at 700 fathoms. Just way too cool!

Greg