[Anthony A.]

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?

 

[smokinghot]

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.

 

[sr20rocket]



Quote:
Originally Posted by Anthony A. /forum/post/16853320


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

 

[budk]

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!

 

[Terry Montlick]



Quote:
Originally Posted by sr20rocket /forum/post/16854208


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.

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

 

[Dennis Erskine]

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.

 

[Anthony A.]

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.

 

[Cathan]



Quote:
Originally Posted by Anthony A. /forum/post/16855166


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.

 

[Anthony A.]

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.

 

[Dennis Erskine]



Quote:
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.

 

[sr20rocket]



Quote:
Originally Posted by Terry Montlick /forum/post/16854298


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.

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.

-Rick

 

[Anthony A.]

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.

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?

 

[Terry Montlick]



Quote:
Originally Posted by Anthony A. /forum/post/16892829


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.

 

[Ted White]

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.

 

[KNKKNK]

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/showt...5#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

 

[slider33]

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

 

[Ted White]



Quote:
Originally Posted by slider33 /forum/post/16895575


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.

 

[slider33]



Quote:
Originally Posted by Ted White /forum/post/16895625


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.

 

[Terry Montlick]



Quote:
Originally Posted by slider33 /forum/post/16895575


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.

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

 

[Ted White]

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