I am beginning my theater construction and would like to keep a separate thread for all my questions and uncertainties. I am trying to keep my room as isolated as possible and hence i have a few questions. the theatre consists of 3 walls that share an exterior concrete wall and are placed approx. 1" away from the concrete. there is only 1 wall that will be an interior wall which will be 2x6 staggered construction.

1.) i have built the exterior walls of the theater room 1/2" short of the main floor joists. i was planning to use dc04 clips to attach them but right now i have used 1 nail every 3-4 feet to attach the wall to the floor joists. i will be installing a new, independant ceiling for the theater completely decoupled from the main floor joists. this includes having new ceiling joists for the theater. as we stand, the wall is very secure even with only 1 nail every 3 feet. is this method okay and can i omit using the rsc-dc04 clips?

2.) in regards to hvac, i would like to have 2 supplies and 2 returns for the room. room size is 15'x21'. i am flexible with placement as this is a new construction home, so what is the best advice for placement? should i have 1 supply and 1 return low wall, and 1 supply and 1 return high wall?

3.) i will be using dd and gg for the entire room, in addition to 1 staggered wall that joins the bar area which will have dd and gg on the other side as well. is using 2 sheets of 5/8" with gg in between sufficient or will i gain anything by using a 3/4" sheet, followed by gg and then another 5/8" sheet?

I am no pro but here's some of my limited insight to your questions...

1) Could you expand a little on your future ceiling's construction? Are you planning on installing a completely separate set of ceiling joists, that will be fastened to your interior walls?

Assuming that is the case, may I suggest you fore go the use D/GG/D and instead use OSB/GG/D. With the added shear support the use of a OSB layer will give you, I don't see the need to connect your new internal walls to the exsiting floor joists. To be very clear... I am not a structural engineer, and/or building inspector, so my opinions are just that, and are not meant to imply that what I suggest is an acceptable way to do things according to building code. However, I am getting the impression that you are planning a room within room build, and I feel using anything to couple your efforts to the existing structure will hamper the end result.

With that said... What I am suggesting is exactly how I plan on to handle my room within room build.

2) If your build is a truly dedicated HT, I think you should concentrate on removing heat from your room. So that lends me to believe a high location for your returns would be best.

3) I think everyone here agrees that the more mass you have the better off your are. Where diminishing returns start to come into play...I don't know.

3.) i will be using dd and gg for the entire room, in addition to 1 staggered wall that joins the bar area which will have dd and gg on the other side as well. is using 2 sheets of 5/8" with gg in between sufficient or will i gain anything by using a 3/4" sheet, followed by gg and then another 5/8" sheet?

If I recall correctly part of the equation that makes DD+GG work is that the two layers should be the same thickness. Different thicknesses of Drywall have different flex characteristics and it was always my understanding that in order for the green glue to work efficiently you needed to make sure the two layers were the same thickness. I believe 5/8" drywall was always the recommended thickness just due to the cost and availability side of things.

-Rick

Not true. You can use different thickness's of drywall but thicker means more mass. More mass is what you want. Having said that... most use 2 layers of 5/8" although some have gone to 3 layers!

If I recall correctly part of the equation that makes DD+GG work is that the two layers should be the same thickness. Different thicknesses of Drywall have different flex characteristics and it was always my understanding that in order for the green glue to work efficiently you needed to make sure the two layers were the same thickness. I believe 5/8" drywall was always the recommended thickness just due to the cost and availability side of things.

-Rick
Not really, Rick. There are two schools of thought on this.

One says you should always used the max thickness for both layers to give maximum mass, and therefore maximum isolation.

The other says you should use two different thicknesses, e.g. 5/8" and 1/2", to circumvent a potentially nasty sound isolation problem called "concidence effect." The latter is a dip in the isolation curve which occurs at 2-3 kHz, due to the bending sound waves in the sheet of drywall coinciding with the speed of sound in the sheet. This frequency changes with the thickness of the drywall sheet, so if you use two different thicknesses, the coincidence dips don't coincide, and the isolation from one sheet fixes the coincident dip of the other.

I tend to favor the latter approach, particularly after I have come from the lab and seen some rather extreme measurements of coincidence dip. :eek: But the thing is, the real-world severity of this effect is hard to predict. Two walls, built ostensibly the same, can exhibit different degrees of coincidence dip. I don't know why.

Regards,
Terry

Mass:
TL = 20 log10 (ms*f) - 48
Effectively means doubling the mass reduces transmission by 6dB. There's a point at which doubling the mass becomes a poor economic choice.
---
Coincidence Dip
While thickness plays a role, stiffness (modulus of elasticity) plays a larger role. At BNR and another secure but undisclosed location, the elasticity of common building materials (drywall, plywood, mdf, etc) were significantly inconsistent from sheet to sheet. Further, variations in method of construction would also alter boundary stiffness. For example, mounting drywall horizontally over 2x4 framing, 16" O.C. would produce significantly different results than when mounted vertically. Two layers of drywall, say 3/8" + 5/8" will behave similar to a 1" layer of drywall when those two layers have been glued together. Two layers of drywall, as above, will more closely mimic two individual layers with a viscolastic agent between layers.

so dennis, are you saying that using a 3/4" and 5/8" is better than 2 5/8" simply because there is more mass? would you recommend i do this instead or just go ahead and use the same 5/8" all around.

so dennis, are you saying that using a 3/4" and 5/8" is better than 2 5/8" simply because there is more mass? would you recommend i do this instead or just go ahead and use the same 5/8" all around.

I don't think you'll find 3/4" drywall. 5/8" is about as thick as I've ever seen it.

okay, i guess i'll just do double 5/8" then. i have also figured out the hvac portion of the theater and will have 2 low wall supplies at the rear of the room, and 1 high wall at the front. i will have 2 returns as well, 1 high and 1 low.

i have also figured out the hvac portion of the theater and will have 2 low wall supplies at the rear of the room, and 1 high wall at the front. i will have 2 returns as well, 1 high and 1 low.
Nah...don't think so. You'll want two supplies (typically in the front of the room, high mounted) and two returns (high mounted) in the back of the room. You do not want air flow directly on any seating location. You do not want a velocity of more than 250 FPM through any vent (diffusor). You want the HVAC system to maintain a temperature of 70 degrees F with an outdoor temperature range of -30 to 100 degrees F and to maintain a relative humidity of not less than 25% nor greater than 50%. You want six air exhanges per hour and 15 CFM of fresh air per person.

Not really, Rick. There are two schools of thought on this.

One says you should always used the max thickness for both layers to give maximum mass, and therefore maximum isolation.

The other says you should use two different thicknesses, e.g. 5/8" and 1/2", to circumvent a potentially nasty sound isolation problem called "concidence effect." The latter is a dip in the isolation curve which occurs at 2-3 kHz, due to the bending sound waves in the sheet of drywall coinciding with the speed of sound in the sheet. This frequency changes with the thickness of the drywall sheet, so if you use two different thicknesses, the coincidence dips don't coincide, and the isolation from one sheet fixes the coincident dip of the other.

I tend to favor the latter approach, particularly after I have come from the lab and seen some rather extreme measurements of coincidence dip. :eek: But the thing is, the real-world severity of this effect is hard to predict. Two walls, built ostensibly the same, can exhibit different degrees of coincidence dip. I don't know why.

Regards,
Terry

Thanks for the clarification of the science involved Terry I appreciate it.
Maybe I have been reading to much on here and its time to start my own theater already. :D

-Rick

i would like to know if my current setup is sufficient. this is in regrads to foregoing the use of dc04 clips tp decouple the exterior walls of the theater to the ceiling joists. right now, i constructed my walls 1/2" short of the ceiling joists and there is 1 nail every 4' around the perimeter of the room holding the walls in place. so total number of nails in the theater is like 20. so the only coupling of the exterior walls would be the nail that connects it to the floor joists. is this an okau practice or will it make all my efforts of double drywall, greenglue and independant floating ceiling futile?



another question is in regards to filling the stage with sand. below is a pic of my setup.

http://i471.photobucket.com/albums/rr72/anthony_arci/Theater%20Construction/Layout.jpg

note the area at the bottom of the pic where it shows a large sub box. this is where the sub will be housed. could i make this small area (its about 4'x6') detached from the stage and fill it with sand and forego having to fill the rest of the stage with sand? the lcr speakers (which will be klipsch ultra 2's) will be installed and bolted to the wall and there will be nothing actually resting on the stage. what are your thoughts on this?

i would like to know if my current setup is sufficient. this is in regrads to foregoing the use of dc04 clips tp decouple the exterior walls of the theater to the ceiling joists. right now, i constructed my walls 1/2" short of the ceiling joists and there is 1 nail every 4' around the perimeter of the room holding the walls in place. so total number of nails in the theater is like 20. so the only coupling of the exterior walls would be the nail that connects it to the floor joists. is this an okau practice or will it make all my efforts of double drywall, greenglue and independant floating ceiling futile?

The nails will not provide wall to joist decoupling. If you want this, you should replace them with the RSIC-DC04 clips. It is exactly what they were designed to do.

The front wall wall is shared with the stairwell. Stairwells will communicate sound vibration very well. It's advised not to incorporate that stairwell wall into the build.

Hello Anthony,

I noticed a post of yours in another thread, that kinda sent up same red flags for me...

http://www.avsforum.com/avs-vb/showthread.php?p=16884895#post16884895

Are you really planning on using 2x4 for Joists, as your independant "Floating Joists"? Spanning 15' unsupported, then hanging 2 layers of Dwall.

Not only will this not pass inspections, but you can expect some serious ceiling sagging in the future.

I didnt take the time to look it up, and I'm no structural engineer but even at only a 15# dead load, i would bet you need a min of probably 2x8, to span 15'.

If you dont have the ceiling height below or the room between your current joists because of mechanicals, for larger joists then you would be better off with clips / channel / current joists to decouple your ceilings. IMHO

If I misunderstand what you mean by floating ceiling or i read your intentions wrong then I apologize and disregard this post.

Brad

I don't mean to hijack, but I have a question that probably serves the thread well.

For a basement theatre, what is the best course of action for the ceiling?

1. Z-Channel and 5/8" drywall
2. Z-Channel and doubled up 1/2" drywall/green glue
3. Doubled up 5/8" drywall without the channel (right onto joists).

I am going to use pink QuietZone all round the room and in the floor (basement ceiling) joists. I am trying to not go too expensive so these are the best options for me I think.

I have only read about Z-Channel, is it readily available at a place like Home Depot? How much is it?

Thanks guys

I don't mean to hijack, but I have a question that probably serves the thread well.

For a basement theatre, what is the best course of action for the ceiling?

1. Z-Channel and 5/8" drywall
2. Z-Channel and doubled up 1/2" drywall/green glue
3. Doubled up 5/8" drywall without the channel (right onto joists).

I am going to use pink QuietZone all round the room and in the floor (basement ceiling) joists. I am trying to not go too expensive so these are the best options for me I think.

I have only read about Z-Channel, is it readily available at a place like Home Depot? How much is it?

Thanks guys

I would not use Z-Channel. Too stiff. Here's what is recommended starting from the top and working down in terms of performance:

#1 a Floating Ceiling. Best, most complete decoupling. Uses simple lumber

#2 Use Resilient Clips and Drywall Furring Channel

#3 Use the Drywall Furring Channel attached directly to the joists. Attach drywall to the channel. Channel is 24" on center

#4 Attach drywall directly to the joists.

In the joist cavities use dtandard (cheap) R19 fiberglass. Shop for the best price.

Use double 5/8" drywall. It's too cheap no not use 2.

I would not use Z-Channel. Too stiff. Here's what is recommended starting from the top and working down in terms of performance:

#1 a Floating Ceiling. Best, most complete decoupling. Uses simple lumber

#2 Use Resilient Clips and Drywall Furring Channel

#3 Use the Drywall Furring Channel attached directly to the joists. Attach drywall to the channel. Channel is 24" on center

#4 Attach drywall directly to the joists.

In the joist cavities use dtandard (cheap) R19 fiberglass. Shop for the best price.

Use double 5/8" drywall. It's too cheap no not use 2.

Pardon my ignorance, but what exactly is a resilient clip? Is the furring channel the same thing as a Z channel? I only have an 8' ceiling down there so I don't think I'll have the space for a drop ceiling.

I have only read about Z-Channel, is it readily available at a place like Home Depot? How much is it?

If you mean "resilient channel," fugetaboutit. :D It used to be an option for sound isolation, but has proven:

1. Unreliable to install, because of the likely possibility of installers shorting it out with long screws.

2. Unpredictable, due to product change/variation and lack of testing for new versions.

The replacement for these are RSIC -- Resilient Sound Isolation Clips, distributed by PAC International.

- Terry

Great question. A Z-channel is used for other things, but not ideal for this application. Distinctly different animal from a Drywall Furring Channel. See various clips and applications here: http://www.soundproofingcompany.com/products/clips/

My apologies for the commercial nature of this link. You can see various types and how they are applied

Thanks for the help guys

Just a little interesting tidbit. Holmes on Homes episode this weekend had the big man using hat channel. In his explanation he said that they only fastened it on one side so that it would hang down and act like a spring for sound proofing.

Kind of a poor man's Z channel if you ask me. Also struck me as a little risky to use it in a manner it wasn't intended.

Wow. What a liability

The nails will not provide wall to joist decoupling. If you want this, you should replace them with the RSIC-DC04 clips. It is exactly what they were designed to do.

how much flex do the dc04 clips have in terms of measurements? (ie. can i push the wall 1/4" in)

The front wall wall is shared with the stairwell. Stairwells will communicate sound vibration very well. It's advised not to incorporate that stairwell wall into the build.

what would be your suggestion ted? that wall is a 2x4 bearing wall resting on concrete, but i can add a 2x2 plate on the bottom and top and use more 2x4's to make it a staggered wall. this is will be covered with dd and gg on the theater side, but single layer on the stair side. or would you recommend resilient clips, etc?

Hello Anthony,
Are you really planning on using 2x4 for Joists, as your independant "Floating Joists"? Spanning 15' unsupported, then hanging 2 layers of Dwall.

Not only will this not pass inspections, but you can expect some serious ceiling sagging in the future.

Brad

i thought so too until my carpenter advised me that it is standard practice to use 2x4's vertical and then use either 1 or 2 perpendicular pieces to tie them together. i asked an engineer who is a friend of mine, and he said that will be much stronger than if i were to use 2x6 verticals. aparently the span is by code as well, so we'll see tomorrow how it goes. if i find i can't hang from them ;), then i'll beef it up with something bigger. this method is used when reinforcing roof trusses and is quite solid when completed braced and nailed together.

i thought so too until my carpenter advised me that it is standard practice to use 2x4's vertical and then use either 1 or 2 perpendicular pieces to tie them together. i asked an engineer who is a friend of mine, and he said that will be much stronger than if i were to use 2x6 verticals. aparently the span is by code as well, so we'll see tomorrow how it goes. if i find i can't hang from them ;), then i'll beef it up with something bigger. this method is used when reinforcing roof trusses and is quite solid when completed braced and nailed together.

Sounds like engineered web joists... in which case yes these are stronger and can span farther than dimensional lumber of "=" size.

in regards to insulationg a ceiling, i need some help. i have 2x10 joists, followed by a 6" air space, and then a 2x4 independant floating ceiling for my theater. so total joist air space is about 20". other than the fact that anything more than r12-19 is sufficient, is it advisable to stuff this entire 20" air space to avoid resonance, or can i simply put up r19 at the top of the 2x10 joists and have about 15" of airspace in the cavity? will this act like a drum and should i competely insulate this space?

Your earlier posts describe walls build within 1/2" of your existing joists, at first I thought you were going to rest your new ceiling joists on top of the walls you built (with new joists Weaved between existing joists) to create your decoupled ceiling. Then I read this post that describes the bottom of the new joists being ~ 10" below the existing joists.

Are they using joist hangers off of the walls to carry the new "floating ceiling"?

If you could post some pictures that would be great.. I'm having a hard time wrapping my head around the construction of what you are describing. (maybe i shouldnt post until i have 6 cups of coffee in me :o) sorry about being so dense, but now I'm curious.

Brad

how much flex do the dc04 clips have in terms of measurements? (ie. can i push the wall 1/4" in)
This turns out not to matter, Anthony. The issue is with mechanical decoupling of the walls to the ceiling.

Another option is to use sway braces to hold the walls. But these are not designed to support the walls -- only stabilize while mechanically isolating them. And they tend to be rather expensive compared to the DC04 clips, which provide support as well.

I don't know the details of your configuration. But if you follow the PAC International's installation recommendations on number of DC04 clips, or speak to an engineer there (they are excellent), your wall will also be guaranteed not to fall down. :D

- Terry

you're right, i haven't been too clear, but basically the exterior walls have been built 1/2" short of the existing floor joists. the interior wall that i will be building (staggered one), will be about 10" lower than the existing floor joists' bottom. so the new independant ceiling will be resting on the staggered partition, but the other side will have a ledger nailed to the wall and then joist hangered for support. i hope this is clear, if not by tomorrow night the basement will be finished framing and i'll post some pics in my build thread.

Anthony, I would strongly encourage you to build a new wall system in front of the old theater stairwell. Any contact with that wall will diminish your results.

You really cant contact any existing framing, especially the stairwell framing. Everyone wants to, but not a good idea at all

okay i've been thinking that as well, but in order to minimize lost space, do you think a 2x2 wall is sufficient (spaced about 1/2" away from the stairwall) with 6" insulation between both wall cavities? or is the minimum 2x3 wall also for better support?

2x3 is better for support, but you would not want to compress any insulation. R11 or R13 in a 2x3 wall is OK but getting compressed will allow the insulation to conduct vibration.

Ideally, you would leave that stairwell in the dust and erect a double wall assembly to completely isolate the theater from the stairwell. A 2x3 wall in front of the existing wall would require you to include that stairwell as part of the decoupled framing. Not nearly as good a course of action.

okay, what if i were to leave a 1" gap from the existing stairwall and erect a 2x3 wall that is fastened only to the independant ceiling joists, thus not touching the stairwall. r11 insulation in the 2x3 wall with a little bit coming out of the studs at the back but held in place with a wire strap to keep it in, but not touching the stairwall. then i would insulate the 2x4 stairwall as well, with a single layer of drywall on the stair side, but dd and gg on the 2x3 wall facing inside the theater. so in essence the were would be about 8" of airspace total..... drywall + 2x4 wall with r13 + 1" airspace + 2x3 wall with r11 + dd and gg. do you think this would be okay?

sorry if i appear dense, just want to get it right. thanks again.

Hi Anthony,

You're not appearing dense at all. I think you'll be glad you're looking at this as hard as you are.

Could you:

Come away from that stairwell wall a couple inches and build a new 2x4 wall.
Drywall the side facing the stairs.
Insert R13
Install clips+channel
Double 5/8"

This would get you totally away from the stairwell, and not incorporate the stairwell into the theater walls at all.

So the resilient channel and dd/gg are on the new 2x4 wall on the theater side, and this new wall is not insulated, only the wall that touches the stairsan correct?

This is a great idea ted, although the new wall plus airspace plus rsc channel will easily eat up about 8-9 inches which I don't want to do. What is the next best thing I can do with only using 4 inches or so?

okay here is what i finally did. for the wall touching the stairs, i built a new 2x3 wall that does not touch the adjoining wall. this wall is about an 1 inch away from the existing wall. in essence its a double wall construction. i will either dd and gg it or put rsc clips on it plus dd and gg for the theater side. i have some new questions now.

1.) in regards to insulation, should i install r13 in the 2x4 stairwall and then r11 in the 2x3 wall (with an inch of space between insulation so they're not touching), or should i just insulate 1 wall with r11/r13 and if so, which wall exactly?

2.) the perimeter of the house has been insulated with vapour barrier already. you can see my build thread for pics in post #4 of the room.
http://www.avsforum.com/avs-vb/showthread.php?t=1164966

my question is whether or not i need to, or should put further insulation in these walls to maintain soundproofing. and if so, is this recommended?

3.) in regards to the ceiling, well i have to say that it is sturdy but there is too much flex for my liking. as already stated, i put 2x4's as new ceiling joists and then a vertical 2x4 to tie them all together. can i add a few dc04 clips to the vertical members and tie them into the existing 2x10 floor joists? i realize this may defeat the purpose of an isolated ceiling but i can take the compromise since i don't feel at ease with the amount of flex right now.

Hi Anthony,

I haven't been as attentive to your thread as I would have liked.

Regarding this 2x3 wall parallel to the existing stairwell wall, both the stairwell wall and new 2x3 wall are unfinished? You are combining the stairwell wall with the 2x3 wall to create a double stud wall? As I've said "by the book" this isn't preferred, but we have to matty together practicality with the technicality. Insulate the walls as you have described.

Regarding the flexible ceiling framing, can you sister additional 2x4s to what you have now to stiffen?

no problem ted, thanks for your continuous support on these matters. i realize you told me to do 2x4 wall originally but since im slowly eating away theater space, i have been trying to minimize everything i can within reason and go for 95% efficiency. but yes, that is a double wall construction with a 2x3 wall in front of the existing 2x4 stair wall unfinished. they are not touching so i would assume this would be a double wall construction. just curious, but are you saying the book states to finish the stairwall with drywall on both sides and filled with insulation, and then leave a couple inches of airspace and build a new 2x4 partition which will be drywalled again on both sides and filled with insulation again? if this is correct, i thought it was recommended not to drywall 2 separate walls and leave an air cavity as it will act like a drum. maybe im not understanind this completely.

in any case, would using the rsic clips on the 2x3 wall insude the theater provide me with a much higher stc rating as opposed to 2 layers of dd and gg fastened directly to the new wall?

ps. im looking to put in an order for someone materials either today or tomorrow but the website only shows shipping to US and not canada. do i need to send you a pm for the list of materials i need and then pay with cc? or do you accept paypal?

Hi Anthony,

We ship to Canada almost daily. Just give us a call.

In that double stud config, there's no need for clips and channel. THe double wall is already considered a "decoupled" assembly.

okay thanks ted. i'll be back in a few hours and give john a shout.

would it be a no-no to use 3/4" mdf for the front wall of the theater and "sub area" to make it denser, followed by a layer of gg and then 5/8" drywall? im thinking the mass would be better than 2 layers of drywall but would like to make sure if it will be better since it is a lot stiffer than drywall. also, in regards to the "sub area" (which is about 4'x4'), i was thinking of using 2 layers of 3/4" mdf and then a layer of drywall (all with gg in between), to help absorb the sound pressure to the above room. would this be a good idea?

would it be a no-no to use 3/4" mdf for the front wall of the theater and "sub area" to make it denser, followed by a layer of gg and then 5/8" drywall? im thinking the mass would be better than 2 layers of drywall but would like to make sure if it will be better since it is a lot stiffer than drywall.
The densities of MDF and drywall are about the same. These can vary from about 39 pcf to 48 pcf. I generally use the 48 pcf figure for calculations. So maybe the extra 1/8" would make a difference. Maybe not.

Regards,
Terry

Anthony. The entire room is being exposed to the same soundwaves, so trying to reinforce obe small area isn't done.

Also, optimal damping occurs when both sides of the Green Glue sandwich are the same stiffness. Double 5/8" drywall is the way to go.

i know it has been stated many times (and most here do it) but im wondering if i can get away with it. specifically, the aquarium tank analogy is used to seal off the room with dd and gg and then one builds their stage, soffit, etc. im looking to build a bulkhead on the front ceiling that will mimic the design of the stage. originally i was going to dd and gg then entire room first and then build this ceiling bulkhead. im wondering now if i can get away with building it and drywalling it with the rest of the room. all seams will be covered with acoustical sealant and the edges will be taped and mudded before the second layer of dd and gg goes on. do you think this will be okay in regards to sound isolation? im going through the trouble of double stud construction, independant floating ceiling, dc04 clips, etc. i don't want to short-circuit my efforts but it would be a huge timesaver to build the bulkhead now. any opinions?

Hi Anthony,

You can certainly do this. Decoupling is a key component to isolation, but you can decouple the frame from the joists, and then attach drywall directly to the decoupled frame.

OR

You can build a coupled frame directly to the existing joists and then decouple the drywall from the frame using resilient clips.