Author Topic: Question about drywall framework  (Read 5556 times)

xelanoimis

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Question about drywall framework
« on: June 19, 2013, 09:01:13 AM »
Hi,

I'm trying to isolate a basement for a personal home cinema and I have a question about the mounting of the drywalls. I will first present the details of the project and post the question at the end.

The room is 2.4m (7.8ft) height, 1m (3.2ft) above ground with 2 small windows. Area is about 4x4m (13x13ft). Walls are thick concrete. One concrete reinforced beam traversal in the middle. The floor is also concrete. Other people live only above, not in other basements. Destination is personal home theater with medium levels of sound power and bass.

For the ceiling I plan to use HD Foam Plus+ (Heavy Foam) 5cm (1.9'') glued with Durabond D-332 which is sold as acoustic glue (I don't have access to green glue). The central beam will also be covered. And the HD foam will be turned on the lateral walls a couple of inches. This is professional standard but for the walls I'll try to skip on the costs a bit and use mineral fiber wool of 10cm (3.9'') thick and higher mass/density (90 kg/m3 = 198lbs/m3).

Over this layer of insulation I want to add heavy drywall, 2 sheets glued together with the D-322 glue, similar to your standard green glue drywalls.

I want to have as few contact points as possible between the drywall and the concrete walls or ceiling (decouple them).

For ceiling, I want to attach the standard metal framework (called UD30) round the walls, just below the ceiling insulation, forming a rectangle and inside this rectangle place the rest of the traversal metal frames (called CD60) to attach the drywall boards. This is standard procedure, except the connection with the walls will be through some special pieces (similar to the professional ones) to avoid transmitting vibration into the walls (also in the standard procedure there might be some direct connections with the ceiling which I'll avoid).

The size of this drywall rectangle will be about 4x2m (13x6ft) and there will be 2 such areas on the ceiling (separated by the central beam). Considering the small size of it it should be rigid enough not to bend or anything.

But from the soundproof point of view, I wonder if this installation (without connections to the concrete ceiling but only to lateral walls) will work well, hopefully for low frequencies too.

What I fear is not to make a mistake and have it behave like a drum membrane and actually amplify the sound.

The walls will be done in a similar way, with connection to the top of the wall (same special pieces) and to the floor.


Please give me some advice.
Thanks a lot!
Alex

Randy S

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Re: Question about drywall framework
« Reply #1 on: June 19, 2013, 03:40:42 PM »
Your system is valid, do not do the perimeter frame , only do the field if possible. You do not want a hard connection around the perimeter of the room.. make sure you leave the ceiling drywall 1/4" off of the walls you fill this gap with acoustical caulk (each layer of drywall). Same process when meeting the beam.
Try to make the least amount of connections to the ceiling using a type of hanger for these channel.
Also use a form of padding tape on the channel prior to hanging drywall, this will help dampen the metal channel.
Good Luck with your project, feel free to post your results or contact if you have questions.

Randy S.


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xelanoimis

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Re: Question about drywall framework
« Reply #2 on: June 21, 2013, 07:36:16 AM »
"do not do the perimeter frame , only do the field if possible (...) make the least amount of connections to the ceiling"

I was planning to do the perimeter frame and connect it to the walls especially to avoid any connections with the concrete ceiling. This way the whole ceiling framework with the drywall will hang from the lateral walls (and beam), with special anti-vibrations connectors.

I am hopping it's more efficient to connect to lateral walls instead of the ceiling, unless this structure would not behave like a drum membrane and do more harm than good.

Please let me know if this will work well.
Alex


jhbrandt

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Re: Question about drywall framework
« Reply #3 on: June 22, 2013, 04:37:13 PM »
....The room is 2.4m (7.8ft) height, 1m (3.2ft) above ground with 2 small windows. Area is about 4x4m (13x13ft). Walls are thick concrete...

Hi Alex, a few points so far; your room is a CUBE and it is a concrete 'bunker'. This means that your bass distribution will be poor AND it will resonate almost uncontrollably. My calculations on your room dimensions show that you will not have good modal distribution below the 125Hz 1/3rd ocatve band. You will also have coincident resonances beginning at 43Hz.. and doubling on up the spectrum. At 215Hz you have axial modes and Tangential modes combining to reek even more havoc.
You WILL need some serious trapping, preferrably limp mass membrane trapping to get this even close to under control.
I highly recommend that you do one of these two options; 1. find another more suitable room, or 2. Move a wall.
Sorry, there is no magic bullet and to quote Scotty from Star Trek, "Ye canno' change th' laws o' physics!!"

For the ceiling I plan to use HD Foam Plus+ (Heavy Foam) 5cm (1.9'') glued with Durabond D-332 which is sold as acoustic glue (I don't have access to green glue). The central beam will also be covered. And the HD foam will be turned on the lateral walls a couple of inches. This is professional standard but for the walls I'll try to skip on the costs a bit and use mineral fiber wool of 10cm (3.9'') thick and higher mass/density (90 kg/m3 = 198lbs/m3).

HD Foam Plus+ is a half open cell/half closed cell polyurethane foam. As acousticians, we never recommend a closed cell foam configuration for acoustics, it is useless. What you REALLY need is MASS and cavity absorption. You can not beat it with ANYTHING. Green Glue is a CLDM (Constrained Layer Damping Material) and it works for additional damping which, in turn, lowers the panel resonances and improves the transmission loss.

For cavity fill, it has been well documented in ir761 (available on my publications page) that a lightweight fiberglass fill is superior to any other more costly or exotic absorbent.

For general acoustics, densities greater than 70kg/m3 are not recommended.

...I want to add heavy drywall, 2 sheets glued together with the D-322 glue, similar to your standard green glue drywalls.
..........between the drywall and the concrete walls or ceiling (decouple them).

This is good. Use a fire-rated gypsum board as these have a denser core and are therefore heavier.

For ceiling, I want to attach the standard metal framework (called UD30) round the walls, just below the ceiling ....

This approach is good. Be sure to caulk the perimeter well. See post #6, http://supersoundproofing.com/forum/index.php/topic,3794.0.html

But from the soundproof point of view, I wonder if this installation (without connections to the concrete ceiling but only to lateral walls) will work well, hopefully for low frequencies too.

Wall connections; use a good decoupling product. This will be money well spent. - Also, depending on the depth (height) of the ceiling cavity, you may want to add a 3rd layer of gypsum board to lower the resonant frequency of the ceiling assembly. At 2.7 meters, you are not going to have much room to 'play with'. ;)

Alex, your ceiling will work, but the room may not. please be aware. Do without the hd foam stuff and go with regular building insulation to fill the ceiling with.

When you build out your front, back, and side walls; change the dimensions so that they do not have a common denominator. - AND you'll be FINE! ;)

Cheers,
John

xelanoimis

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Re: Question about drywall framework
« Reply #4 on: June 26, 2013, 09:40:22 AM »
Thanks for the detailed answer, John.

I read through the publications you mentioned. Really interesting stuff, that I wasn't aware of. Especially "How to find out how much Isolation you need" and ir761 and ir586.

The conclusion I draw is, as you said, to use regular light glass fiber in the cavity and 2 sheets of gypsum (we even have a soundproof gypsum, blue one, with higher mass than the others).
I will also try to avoid contacts with the ceiling and to use special connections with walls, to decouple it. I'll be back with questions about this later.


1. One question about the with the light glass fiber insulation: How do I hang it behind the vertical drywall?

Initially, I was thinking of a 10cm cavity filled with heavy mineral fiber and then have the vertical metal profiles of about 3x6cm with the 6cm to the drywall. So the gypsum boards would stay at about 3cm from the solid insulation. Now that I plan to use light glass fiber in the 10 cm cavity, I fear this kind of insulation will fall or compress in time, behind the wall. So how should I fix it? Should I mount the vertical metal profiles with the 3cm side to the drywall so the form a better segmentation for the insulation to sit in? There is a sort of such glass fiber with a metallic layer for avoiding humidity pass. Could this serve as a better support?.

I suppose for the ceiling, I just push the insulation to fill the gap. It will sit on the gypsum board? But will it compress in time and create an air cavity above, to the ceiling?


2. Another question is about the 2 boards of gypsum. I wanted to glue them together, but since I don't have green glue, I wonder if I should try some strips of the sound isolation tape (like mentioned somewhere on the forum), or even strips of MLV glued between. Also I'm not sure if the gypsum boards will hold together just from the glue, or if I have to screw them to the metal frame (passing through the first layer of gypsum). I suppose ideally there would be just the elastic glue between boards, but I'm not sure it will hold for the ceiling. Let me know if you have a suggestion on this.

Thanks.

jhbrandt

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Re: Question about drywall framework
« Reply #5 on: June 26, 2013, 03:42:49 PM »
Thanks for the detailed answer, John.

I read through the publications you mentioned. Really interesting stuff, that I wasn't aware of. Especially "How to find out how much Isolation you need" and ir761 and ir586.

The conclusion I draw is, as you said, to use regular light glass fiber in the cavity and 2 sheets of gypsum (we even have a soundproof gypsum, blue one, with higher mass than the others).
I will also try to avoid contacts with the ceiling and to use special connections with walls, to decouple it. I'll be back with questions about this later.

You're welcome. You will find that if you compare the MASS of the 'soundproof' gypsum board with the 'fire-rated' gypsum board and their  associated prices, you will usually find that regular fire-rated board is a better 'bang for your buck'.

1. One question about the with the light glass fiber insulation: How do I hang it behind the vertical drywall?
Initially, I was thinking of a 10cm cavity filled with heavy mineral fiber and then have the vertical metal profiles of about 3x6cm with the 6cm to the drywall. So the gypsum boards would stay at about 3cm from the solid insulation. Now that I plan to use light glass fiber in the 10 cm cavity, I fear this kind of insulation will fall or compress in time, behind the wall. So how should I fix it? Should I mount the vertical metal profiles with the 3cm side to the drywall so the form a better segmentation for the insulation to sit in? There is a sort of such glass fiber with a metallic layer for avoiding humidity pass. Could this serve as a better support?.

Building insulation for walls usually has frk (foil reinforced kraft) paper on one side. You attach this paper to the interior of the studs with a 'hammer tacker' or staple gun. The frk keeps it in place. The frk IS the moisture barrier. ;)

I suppose for the ceiling, I just push the insulation to fill the gap. It will sit on the gypsum board? But will it compress in time and create an air cavity above, to the ceiling?
For the ceiling cavity, use attic blanket. This stuff does not have the frk but is plain fiberglass.

2. Another question is about the 2 boards of gypsum. I wanted to glue them together, but since I don't have green glue, I wonder if I should try some strips of the sound isolation tape (like mentioned somewhere on the forum), or even strips of MLV glued between. Also I'm not sure if the gypsum boards will hold together just from the glue, or if I have to screw them to the metal frame (passing through the first layer of gypsum). I suppose ideally there would be just the elastic glue between boards, but I'm not sure it will hold for the ceiling. Let me know if you have a suggestion on this.

Thanks.

NOPE. No need to glue or add MLV. Normal, regular building techniques apply. The only difference will be at the perimeter intersections, which should only be caulked. (be sure to use a backer rod!) -- ALL YOU NEED IS MASS. It is that simple. MASS and damping - which the insulation in the wall cavity will provide. If you require additional damping use a CLDM like Green Glue. But please note; Green Glue is NOT glue. It is a Constrained Layer Damping Material. (do a google search)
(By the way, MLV is great for damping and quieting a noisy computer. Use the sticky backed stuff and put it on the inside of the thin metal case. But this is a VERY, VERY, Expensive way to get mass when another layer of gypsum board will beat it in performance and price.)

Have fun!
Cheers,
John

xelanoimis

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Re: Question about drywall framework
« Reply #6 on: June 27, 2013, 02:29:54 PM »
All right.

I did some relative measurements, using a set of speakers with a small subwoofer in the basement. I don't have a pro tool to measure sound so I used some iPad app which showed the dB values. I don't expect it to be accurate but still I was able to compare some values. I remind that the room is empty with concrete walls, 2 small pvc windows (about 90x50cm) and a metal door. Next is a small hallway (3m) and then the bottom of the stairs going up to ground floor. I played music and speech (audiobook) at high volume (over the limits I would normally listen).

The resulted values (dB) are as follows:

locationsilencemusicspeech
inside the room40-5095-10088-94
outside door closed40-5070-8065-73
downstairs door opened40-5075-8765-80
downstairs door closed40-5060-7350-65
ground floor40-5055-6545-55
in the street, near window45-5565-7555-65

Even from the ground floor, in the best case (45-55dB), the music/noise was still clearly audible. However my neighbor from ground floor said he didn't hear it. My wife from 1st floor did hear it a bit though. In the street it was not audible unless in front of the windows. Also if I play it at decent volumes (80-90dB music / 70-85dB speech) it was hardly audible from the ground floor (42-54 / 45-55 that is almost the values recorded for silence).

-----------

Obviously my weakest link now is the metal door (about 0.8x1.7m) which I plan to address first. For now, it seems it reduces about 20dB when closed, but it's missing most of its sealing rubber band. I also plant to fill the metal frame with sand (will it work?) because now it sounds hallow when knock on. There's no space under the door (frame all around)

QUESTIONS:

1. Is it worth to seal it with a MLV band (3mm?) glued to the metal frame, pressed by the door when closed, instead of standard rubber band for doors and windows?

2. For the door itself, one idea is to apply a MLV membrane (3mm) glued on the door (facing the inside of the room) and then maybe HD foam or similar of 5mm? My purpose is to stop the sound to pass through the door.

My access to sound proof materials is a bit limited: HD foam (most probably a similar lesser product than the original), BlockTec (also possible not original, similar in purpose to MLV), MLV (original and expensive, sold in roles), cork boards, egg-like foam. More options for acoustic materials though.

A good thing is that I can add another door between the small hallway and near the bottom of the stairs.

I will keep track and do more tests during progress and post it here for reference.

So, if you can give some advice for my door, please do.
Thanks,
Alex

jhbrandt

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Re: Question about drywall framework
« Reply #7 on: July 11, 2013, 06:53:56 AM »
Alex,

1. hmmm probably not, I doubt that the MLV will compress enough to seal, besides - it's not made for that sort of thing. Look into automotive trunk rubber. There are several forms that can be adapted to soundproof doors. ;)
2. Good idea! Unless you want to use poisonous lead.. just kidding. An MLV sheet on the door will add some good weight without taking up much space AND it * nicely. The foam is a good idea too, but not for the purpose that you had in mind. ;) The foam will present an absorbent to that side of the door and reduce reflections from the surface of the door - it will not improve the soundproofing properties of the door.

Also note: materials sold as 'cheaper substitutes' and do not have testing data - I do not recommend. That would be like throwing good money after bad. Save your money and get the stuff that has testing data on it. The SuperSoundProofing guys have a very good HD MLV, that I would recommend if you are buying MLV. - Foam; look at the 'good stuff' with testing data, save your money and buy that. Now, you have an 'investment'. None of these things, especially these days, should be thought of as 'disposable'. ;)

Cheers,
John