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 Post subject: Ceiling Construction
PostPosted: Fri Jul 27, 2018 7:19 am 
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Location: Palmer Lake, Colorado USA
Hello Everyone,
I just found this forum and it has a lot more knowledge here than others I’ve visited. I need all the help I can get.

Hopefully I can give enough of a detailed explanation that you can help me with the information I need.
I’m building a rehearsal space/studio in an unfinished room in the basement of my house. I have attached a preliminary drawing that I hope will help. My question is regarding the ceiling.

The ceiling is approximately 9 feet high and the floor joists (TJI) are spaced on 12 inch centers for the most part. I have already installed one layer of 5/8” sheetrock with green glue in between the joists with the seams and edges sealed with acoustic sealant. As you can probably imagine, the amount of time this has taken is amazing. Before I add another layer, I wanted to ask your advice.

Rather than a second layer of rock and green glue I was considering installing a layer of Roxul Safe’n’Sound insulation, capping off the joists with a layer of ½” rock, and then beginning the actual ceiling with IB-1 isolation clips and 7/8” hat channel. From there I will put two layers of 5/8” rock with green glue in between. My reasoning behind this is that I can do this in less time than it would take to add a second layer of rock and green glue in between the joists. I was also hoping that it might result in a little more sound isolation for the room above.

Thanks in advance for any and all replies. Like I said, I need all the help I can get!


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 Post subject: Re: Ceiling Construction
PostPosted: Fri Jul 27, 2018 8:38 am 
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Welcome to the forum dbtech (whatever your real name is)!

Before you post again, please read the Forum Rules!!! and fill out the rest of your profile. The forum is very strict about this. It's all free advice, so be respectful and kindly follow the rules.

Quote:
I’m building a rehearsal space/studio in an unfinished room in the basement of my house.

This indicates that you will be very loud rehearsing. If you would have read the forum rules, you would have known to measure and post your desired/required amount of isolation. We REALLY can't advise you on your build without this information.

Maybe your roomates/family are okay hearing the drummer fart or maybe they don't want to hear any noise from your band. You haven't told us, so as you can see, we don't know how extreme you want your isolation.

I see you're making some effort to contain the energy in your basement, however, with the building techniques you're using, you aren't going to achieve great results.

Quote:
Hopefully I can give enough of a detailed explanation that you can help me with the information I need.

Not enough information :-(

Quote:
The ceiling is approximately 9 feet high and the floor joists (TJI) are spaced on 12 inch centers for the most part. I have already installed one layer of 5/8” sheetrock with green glue in between the joists with the seams and edges sealed with acoustic sealant.

You're blessed with a higher than average basement ceiling! That's a great thing.

How did you mount the sheetrock to the subfloor above?

Did you box in any existing ducting, electrical, gas, plumbing? If not, you have to. The surface density of plumbing pipe and the penetration through the main subfloor will trash your isolation. I know, this will create a three leaf system, but in these circumstances, there is no way around it. Ideally, you want your middle leaf to have a ton of mass, so when you box these in, use a lot of mass (at LEAST an 1" of MDF for example.

Quote:
Rather than a second layer of rock and green glue I was considering installing a layer of Roxul Safe’n’Sound insulation

No matter what, you need to dampen that cavity with insulation. Safe'n'Sound has pretty great absorption coefficients for low cycles so that's a good option.

Quote:
capping off the joists with a layer of ½” rock

I assume you mean the ends of the joists above your frost wall? Yes, you will have to cap off where you stopped beefing up your ceiling and where your inner leaf will meet it (assuming you're not building an MSM system). However, you have to maintain the surface density throughout your build. So, that "cap" we are talking about, it has to have the same surface density as your flooring above, subfloor, and the 5/8" drywall beef you added. Otherwise, the end caps will be your weakest link and you'll only achieve the level of isolation that it provides (1/2" drywall). Also, make sure to use heavy fire rated drywall, not this new ultralight crap that every box store carries!

Quote:
and then beginning the actual ceiling with IB-1 isolation clips and 7/8” hat channel.

Sure, you can do this as long as you're aware that your low frequencies will penetrate the rest of your home worse than they do at this moment. The high frequencies (which are probably already not horrible throughout your home) will be attenuated as expected, but it's usually the low end that annoys roommates and neighbours. So, if that were my place, I wouldn't use that system. Again though, you haven't told us the whole story. Maybe you live alone and your nearest neighbour is 1km away.

Quote:
From there I will put two layers of 5/8” rock with green glue in between.

This would probably be enough mass for an MSM system, but since you'll have a coupled system, you're going to be relying on Mass Law Equation. It states that you need to double your mass for every 5 dB of transmission loss. That's not good. ALSO, you need to contact and get a structural engineers stamp in order to have all of this extra mass on those TJI's. Whoever designed your joist layout probably only accounted for a single layer of ultralight 1/2" drywall to be anchored to the bottom of those joists. Not THREE layers of 5/8" heavy drywall plus clips, hat, and insulation. Also, your room is going to sound like butt after you have all of that drywall on the ceiling. Therefore, you're going to be hanging 1x6" framed broadband panels off of it which will add a ton more weight. You NEED to get this approved. The crappy thing about channel is that it's typically only rated to hang two layers of 5/8" off of. So when it doesn't isolate good enough, you're going to want to add more layers (remember, to get only 5 dB more isolation, you're going to have to add TWO MORE 5/8" layers to it.

Quote:
My reasoning behind this is that I can do this in less time than it would take to add a second layer of rock and green glue in between the joists. I was also hoping that it might result in a little more sound isolation for the room above.

Sure it'd be faster. You're going to need that extra drywall on the bottom anyway. Here's the thing:

If you're already planning to mount two layers of 5/8" drywall on the bottom side of those TJI's, you're also going to need acoustic treatment panels hung up there. You're already going to have to get an engineer's stamp to do that. SO, why don't you shoot for AMAZING isolation and build an inside out fully decoupled room in a room for your basement. The only extra added expense would be some LVL stud for your inner leaf ceiling joists. It would sound way better, maintain MORE height, and actually isolate super well. If that were my place, that's what I would do. If you don't, I have a feeling it will perform below your expectations and you will wish that you had done it John Sayer's way the first time. However, like I said 47 other times already, maybe you don't need that much isolation.

Lastly, you haven't mentioned HVAC at all. This is a HUGE part of a room design. Think, you're spending all of this time and money adding mass to your ceiling, and then you're going to go and cut big holes and pipe in duct work that will just act like opening a window to the rest of the house and outside world. You might as well not even build the basement out if you're not going to deal with the HVAC properly!

I hope this helped. Again, right now, go and read the forum rules, fill out your information, then respond. I look forward to your response. We're only here to help!

Greg

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 Post subject: Re: Ceiling Construction
PostPosted: Fri Jul 27, 2018 9:43 am 
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Hi there. As Greg already said, please read the forum rules for posting (click here). You seem to be missing a couple of things! :)

Quote:
The ceiling is approximately 9 feet high
That's a good thing.

Quote:
I have already installed one layer of 5/8” sheetrock with green glue in between the joists with the seams and edges sealed with acoustic sealant.
Did you check with a structural engineer before you did that? You placed a lot of extra dead load on those joists, so you do need to get a strauctural engineer to sign off on that.

Quote:
Rather than a second layer of rock and green glue I was considering installing a layer of Roxul Safe’n’Sound insulation, capping off the joists with a layer of ½” rock,
That would create a 3-leaf system, which would potentially REDUCE your total isolation, especially in the low end.

Quote:
and then beginning the actual ceiling with IB-1 isolation clips and 7/8” hat channel. From there I will put two layers of 5/8” rock with green glue in between.
That would DEFINITELY trash your isolation! You would be creating a 3-leaf system of the worst possible kind: very low mass on the middle leaf, and the third leaf over a very thin air gap, thus having a very high MSM resonant frequency. For those occasional cases where there is no choice but to do 3-leaf, the most effective way of doing that is to have MOST of the mass on the middle leaf, and larger-than normal air gaps on BOTH sides of that. You would be doing the exact opposite, making the 3-leafs system perform at it's worst, thus trashing your isolation.

Quote:
My reasoning behind this is that I can do this in less time
Studio building is not about "less time" or "lower cost": it is about doing things the right way to get the results you need. Generally, that takes longer than you first thought it would, and costs more than you first thought it would.

Quote:
I was also hoping that it might result in a little more sound isolation for the room above.
No. It would to the opposite: 3-leaf is always to be avoided wherever possible, and in cases where there is no choice (such as an existing 2-leaf structure that cannot be modified for legal or structural reasons), the solution is to add a lot more mass on the middle leaf, and a larger air gap than normal for the third leaf.

In addition, I suspect that you would be overloading your joists: adding three layers of 5/8 plus one layer of 1/2 means that you are adding 1.75 inches of drywall, which has a density of around 685 kg/m3. Thus, every square foot of what you are doing weighs about 6 pounds. That's without considering the GG, nails, caulk, cleats, or insulation, so call it more like 8 pounds per square foot. So if your ceiling measures, for example, 10 feet by 15 feet, you would be adding 1,200 pounds of mass to your joists. You didn't say how big the joists are, or what distance they are spanning, but that could easily be an overload.

In addition, as Greg mentioned, we can't say if what you are planning would be "enough" isolation, since we don't know how much you need! You did not state that in your initial post. The starting point for any studio build is by defining how many decibels of isolation you need, and the frequency range where you need it. Based on that it is easy to choose a construction technique and building materials that will provide that amount of isolation. If you don't do that, then you are just guessing, and that's not a good way to design a studio.

I would suggest that you need to first read the forum rules, then provide the missing information here: What is it that you are trying to achieve? How much isolation do you need? Are you planning on doing a proper "room-in-a-room"? Is this just a rehearsal room, or also a control room (for mixing/mastering)?

The more information you provide, then more we can help you. Right now, with the limited info you have given, all we can say is that what you are planning to do is not going to achieve high isolation (especially for the bottom end of the spectrum, where drums and bass live), and will likely overload the structural limits of your existing joists. We can't be more helpful than that, until you provide all the details.


- Stuart -

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 Post subject: Re: Ceiling Construction
PostPosted: Sun Jul 29, 2018 7:25 am 
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Location: Palmer Lake, Colorado USA
Hi Greg and Stuart,

Thanks for your reply. I have a LOT to learn.

I filled out the profile and took some pictures so you can get an idea what the room looks like at this point.

More info:

- We want to build a room in a room. It should have it's own ceiling so nothing requiring a structural engineer will be hanging from the TJIs.
- We are using wood studs due to the cost difference.
- The floor is a concrete slab on grade. I was planning on carpeting that.
- I would like to have between 85 - 100dB of isolation if I can afford it.
- There is a bedroom above this room so I would like to get as much isolation as possible.
- I would like to keep the budget around $5000.00 if I can.
- The drywall is attached to the subfloor with green glue and drywall screws.
- I replaced the round metal ductwork with insulated flex duct. The main trunkline is wrapped with insulation (there is still some to do). I thought I could extend the duct down to the room with flexible connections and seal the penetrations for the grilles.

As you can see from the pictures, the room is not very far along at this point. Before finding this forum all I had to go on was information from the Soundproofing Company.

At this point I have several 5-gallon buckets of green glue, putty pads for the electrical outlets and switches and the isolation clips.

I hope this information helps clarify a little what I'm attempting. Let me know what more information you need and I will send it your way.

Thanks again for all your help.

Dave


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 Post subject: Re: Ceiling Construction
PostPosted: Sun Jul 29, 2018 10:06 am 
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Quote:
I filled out the profile
:thu:

Quote:
Thanks for your reply. I have a LOT to learn.
No problem! That's what the forum is for! Don't feel bad about not knowing stuff: acoustics is a huge subject, and many parts of it are not intuitive, because sound does not actually behave the way we expect it to, or think it should! It takes a while to get your head around some of the concepts.

Quote:
- We want to build a room in a room. It should have it's own ceiling so nothing requiring a structural engineer will be hanging from the TJIs.
OK, but you should still check with one about how much weight you are adding to the sub-floor above you. There's a design limit to bot the dead load and live load, and since that is the floor of another room, it already has some loading on it. As you add more drywall between the joists, you are adding more mass, which increases the dead load. You do need to make sure you are not overloading it, even if your final ceiling will not be suspended from that.

Quote:
- The floor is a concrete slab on grade. I was planning on carpeting that.
Concrete slab on grade is excellent. Your best friend. But putting carpet on it would be a bad idea. Carpet is a pretty good way of trashing your room acoustics, since it does the exact opposite of what small rooms need.

Carpet absorbs high frequencies very well, mids to a certain extent but randomly and rising with respect to frequency, then does absolutely nothing at all to low frequencies. That's the opposite of what a small room needs. All small rooms need huge amounts of low frequency absorption, some in the mid-range but less and less as frequency rises, with little to none in the high end. Carpet makes your room sound dull, boomy, thuddy, muddy, lifeless, etc.

Secondly, it is on the floor (duh!), which means it destroys the reflections from the floor that your brain relies on to build an "acoustic picture" of the room. All your life, wherever you go, your ears are exactly the same height above the floor, and your brain is very, very accustomed to figuring out the acoustic signature of the room based on the reflections it hears from the floor. If you sit down, your brain recognizes that, and adjusts it's "image" of the room accordingly. It does not use the ceiling or the walls for that, because the distance from your ears to the walls and ceiling changes all the time, many times per second as you walk around, so the "signature" is not constant or consistent. Ceilings are different heights, and when you walk outdoors, there is no ceiling at all! But there is still a floor, and it is still the same distance from your ears as every other floor.

If you have carpet on the floor, your brain no longer has any reflections to use for this.

So forget the carpet. You'll find it really hard to have a good acoustic setup in a room with thick carpet on the floor. It messes up your psycho-acoustic perception of the speaker locations, as well as your ability to determine directionality, so you'll never get an accurate sense of the real sound-stage, and never have an accurate stereo image. Carpet is pretty good at messing with spatial perception.

Have you ever noticed that world-class control rooms practically never have carpet on the floors in the front half of the room? And ditto for pro live rooms / rehearsal rooms? Never any carpet on the floors. There's a reason for that. if you want your room to be the best it can be, do what the pros do, and leave it out.

Quote:
- I would like to have between 85 - 100dB of isolation if I can afford it.
If you have a few million dollars on hand, then you can afford it! :) The very best isolated studio on the planet is arguably Galaxy Studios, in Belgium. They hired the best acousticians in the world, it took them many years and millions of dollars to design and build that place. Basically, each room in the studio is a massively thick concrete bunker that is floated on huge heavy-duty steel springs along with neoprene pads. They get just a fraction over 100 dB of isolation... :) So 100 dB of isolation is a fine goal to have, as long as your pockets are VERY deep. But it's out of reach for pretty much all home studios.

Let me put this in perspective for you: the decibel scale is logarithmic: each time you go up ten points on the scale, that implies you need to block ten times more acoustic energy. A typical stud-framed wall in a house with a sheet of drywall on each side will get you maybe 30 dB of isolation (assuming it is well built). To get 40 dB of isolation, you need to block TEN TIMES as much energy, 50 dB of isolation implies you need to block ONE HUNDRED TIMES as much as the standard wall (10 x 10), 60 dB of isolation means you need to block ONE THOUSAND TIMES (10 x 10 x 10) as much, 70 dB is TEN THOUSAND TIMES, 80 dB is ONE HUNDRED THOUSAND times as much, 90 dB is ONE MILLION TIMES as much, and 100 dB is TEN MILLION TIMES as much isolation as a typical house wall. Thus, Galaxy studios gets about ten million times more isolation than a typical house wall.

OK, so it's pretty clear that even if you want 100 dB of isolation, it's unlikely you will get that. Even 80 dB of isolation is beyond the reach of the majority of home studios. Most home studio builders are satisfied to to get 40-something dB of isolation, very pleased to get 50-something dB, and ecstatically-jumping-up-and-down-yelling-and-screaming happy if the manage to achieve 60-soemthing dB of isolation. The practical limit for a home studio is around 70 dB, which is roughly the flanking limit for the concrete slab on grade. To get more than that, you would have to isolate the slab-and-foundations for the studio from the slab-and-foundations for the rest of the building. You can get up into the 80's like that, with a bit of like. Going beyond that calls for the extremes of floating floors, floating walls, and at the very top end of the scale, floating concrete bunkers.

So, that leads back to the question? Why do you think you need 80 to 100 dB of isolation? What do you plan to do in there that needs such a high level of isolation?

I'd suggest re-thinking your isolation needs, and doing some actual testing with a good sound level meter, to determine how loud things will actually be in your studio, and how quote you have to be outside the studio.

Quote:
- I would like to keep the budget around $5000.00 if I can.
To be very honest, that isn't realistic. From what I can see, your total room area seems to be around 400 ft2, and it looks like you'll be using about 300 of that for the studio. So, 5000/300 = US$ 16 and a few cents per square foot. You mentioned that you wanted to install carpet: the installed cost of decent carpet is around 5 to 6 dollars per square foot, so JUST the carpeting ALONE would have eaten up one third of your entire budget. Drywall installed cost runs to around 3 to 5 dollars per square foot (even for just moderate isolation), so there goes one third of your remaining budget just for the drywall on the ceiling, without even considering the joists or insulation for that, nor anything to do with the walls, or the electrical system, or the HVAC system, or the doors, or windows, or seals....

So I'd suggest that you need to re-think your budget. For high isolation, a more realistic budget would be around US$ 50 per square foot. A better way to get a realistic figure, is to call around a few local contractors and ask for their standard rate per square foot for finishing an unfinished basement as a living room or bedroom. Add 30% to that, and you'll be close.

Quote:
- The drywall is attached to the subfloor with green glue and drywall screws.
Take the screws out, fill the holes where the screws were with caulk, and use cleats around the edges of the drywall to hold it in place. With small thin strips like that, you cannot screw the drywall into the sub-floor, since that causes them to act as one single slid block, and prevents the Green Glue from working. Green Glue acts as a Constrained Layer Damping compound, and it works by damping the bending waves that run along the drywall. By screwing the drywall into the sub-floor, you are preventing the drywall from moving independently of the sub-floor, and thus it cannot act as a CLD. There are also studios that show a single solid block (such as several layers of drywall glued together) has a LOWER coincidence dip frequency than the same bunch of drywall with no glue, and therefore has WORSE isolation in the mid range. Also, Green Glue is NOT glue! (despite the name). It is an acoustic compound, not an adhesive, and it cannot be used to stick things together.

Quote:
- I replaced the round metal ductwork with insulated flex duct. The main trunkline is wrapped with insulation (there is still some to do). I thought I could extend the duct down to the room with flexible connections and seal the penetrations for the grilles.
Not if you want high isolation! Or even decent isolation. Flex duct has very low mass, so it does not stop sound getting through. A duct is basically a huge gaping hole in your wall, through which sound will pour wonderfully, and escape into the outside world. For high isolation, ever single place where a duct penetrates a wall leaf, you need a silencer box. You can use flex duct to link those boxes together, but not to penetrate the leaf. The box itself must penetrate the leaf, with some type of massive "sleeve", to which the duct is attached.

Quote:
As you can see from the pictures, the room is not very far along at this point.
Excellent! Then there's plenty of opportunity to do it right! This is good news.

Quote:
At this point I have several 5-gallon buckets of green glue, putty pads for the electrical outlets and switches and the isolation clips.
You will not be needing the iso clips, so you can send those back and get a refund. The reason why you will not be needing them, is because you already said that your inner-leaf ceiling will rest only on the inner-leaf walls, and therefore will not need any further decoupling.

Quote:
and took some pictures so you can get an idea what the room looks like at this point.
You have the typical situation where you have non-movable "stuff" in some of the joist bays above you, such as HVAC ducts, plumbing, and electrical. Your only option there is to board those up with plenty of mass, and seal them all air-tight. In some cases, that is as easy as putting a couple of sheets of MDF or drywall on the bottom of the joists, with caulk to seal, but in other places you will have to build framing to go around those "things", then put the drywall / MDF on the framing, and seal that. You need to end up with a surface facing you, all around, that is completely free from any penetrations, holes, cracks, ducts, pipes, wires, etc. Just mass with insulation. Once you have achieved that then you can build your actually inner-leaf room within that "shell" that you have created. In some cases, that framing+beefing up is going to eat a long way into your headroom: you'll have to decide how you want to handle that. You could lower the entire inner-leaf ceiling, or you could angle the inner-leaf ceiling to be lower down around those areas and higher up at the other end of the room, or you could build the inner-leaf ceiling to follow the shape of all of that.

- Stuart -

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