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Discussion Starter · #1 ·
Hey all,


I have read just about every topic I can search for on this topic, but have a couple of questions that I may have missed.


1. What is the floating technique? Should the 5/8 be hung vertically and the 1/2 horizontally or are both done horizontally? I do know that if I don't want really wavy walls to mount the top layer horizontal. :D


2. What treatment is normally done with the 5/8 drywall seams? I plan on beading all seams with acoustic caulk before floating the drywall, but what (if anything) should be done with the seams? I imagine taping is not at all necessary, but should any mudding be done? Using acoustic caulk like mud and evening out the seams?


I appreciate any help available on this subject.


Take care.


Sand


BTW, I have finished framing and used the Resilient Sound Isolation Clips that were suggested in a previous thread (thanks for that). They provide a little wiggle, but should help in keeping the sound from travelling up into the main floor.
 

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I've been reading the Acoustics101 document from Auralex and it answers a lot of the types of questions you're asking with regard to alternating drywall directions and sealing the seams with tape and mud.


If you want to check it out, here's the link:

http://www.acoustics101.com/
 

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You can do either with regard to the orientation. Actually, you get better seam coverage with both vertical but offset by 1 stud.


As for the seams, Caulk, tape, and mud the seams on both layers. Don't have to be real careful about the underlayer when mudding but i would get a good layer on there just to hold things in place. If you don't tape, the mud WILL crack over time.
 

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Discussion Starter · #4 ·
Thanks for the info guys.


Bpape, the one thing I do know about drywall is to never mount the outermost layer (i.e. the layer that will be visible) vertically. It is a surefire way to ensure you have a very wavy wall. ;)


Take care.


Sand
 

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Personal choice. I always hang all my drywall vertically. I would rather spend the time with multiple coats to get it smooth working with the depressions on the width of the board. I am no pro and can't get a good smooth seam that I am happy with where horizontal boards meet. With downlighting, that is asking for a nice shadow line the whole way around the room. Just personal preference on my part.


Of course, if you are going to be covering the wall with TS and fabric, it really matters not since you don't have to do a great mud job on either layer then.
 

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Check Acoustic Sciences Corporation's (ASC) web page. It has a lot on quiet wall construction. My company is presently constructing two such rooms for customers. ASC sells a substance called decidamp that it used between the studs and the 1/2 inch resilient channel upon which the sheet rock is mounted. ASC also sells resilient channel with a strip of decidamp where the first sheet of sheet rock attaches. Decidamp goes over the seams and then squares get compressed between the two sheets. First sheet is 1/2 inch green board and the second regular sheetrock. This will all be clear by going to the web page. The outer seems are taped and the wall is acoustically treated with soft and hard absorption and diffusion. The whole wall is then covered with Guilford fabric. ASR is the company which does this part.
 

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When you do double-drywall, do you do it on all 4 walls in the room, or just the partition walls? Seems to me like it would be a waste to do it on the walls that rest against the outer walls of the house (bricks). But would it throw off acoustics if one side is double drywalled and the other side is just single drywalled?
 

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Double drywall is not to isolate sound primarily. It is to stiffen the wall so the wall doesn't resonate. You need stiff walls on all 4 sides.
 

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The double drywall provides sound isolation and low frequency absorption. The joist/stud cavities must be insulated to prevent resonance inside the walls. While 'soft' and flexible walls also provide low frequency absorption, it is not an ideal practice in playback environments. It is non-uniform, largely non-predictable, and may cause problems which cannot be easily corrected. Using walls as diaphramic absorbers is effective if your primary interest is sound isolation. Otherwise, seek other methods.
 

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Dennis, Are you saying that double wall construction is not effective to prevent the wall from resonating and that insulating inside the walls is preferred? Sorry, I got a little lost in your post.


I have a HT room that was built without any tought to sound. See my story here: http://www.avsforum.com/avs-vb/showt...hreadid=147259


A suggestion I received was to insulate and then add another layer of sheetrock and I'm trying to understand the concepts of each. Also, what is TS?


Rich
 

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If I may, I think Dennis was simply saying that double drywall does both keep sound in and make for rigid, predictable wall behavior. The idea of the insulation is to prevent resonance buildup inside the walls and also to help in blocking sound.


Ever listen to a bass drum of a drum set with and without the pillow? Some of the diff is because the pillow is against the head. Some of it is because it absorbs the airborne waves.


I think the suggestion of insulating and then adding another layer is an excellent way to go.
 

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Read the ASC white papers guys. We have a store with seven soundrooms designed with two purposes. One to keep the sound in each room. The second to make the rooms sound good. My HT at home is designed just to sound good. Sound insulation is not an issue. Walls need to be stiff and need to dissipate vibrational energy. Studs should be attached or blocked to the outside wall to avoid stud twang. Studs can be blocked together if a free standing walll. ASC also sells stud dampeners. After the walls are built and doubled sheet rocked, application of acoustical treatment will be necessary. Bass traps will also be necessary in most rooms. Bass traps besides dealing with bass resonances also relieve back pressure on the midrange drivers.
 

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Quote:
A suggestion I received was to insulate and then add another layer of sheetrock and I'm trying to understand the concepts of each. Also, what is TS?
Insulation within the stud/joist cavities provides two primary functions: (1) any air cavity can become a resonance chamber like the body of a guitar or violin; and, (2) the insulation will assist in sound isolation ... not only sound leaving the space, but external sounds entering the space and raising the noise floor in the room.


Double layers of drywall will: (1) stiffen the walls preventing the wall from becoming a diaphramic absorber of unknown (in advance) properties; (2) provides additional transmission loss characteristics in the low bass regions to assist in sound isolation; and, (3) is helpful in the absorption of lower frequencies to achieve a proper RT60 (in residential spaces the more serious problem typically occurs in the 250 to 500 Hz range).


"TS" and "TS+" refers to a Johns-Manville product called Theater Shield. This product is no longer manufactured and the one used in its place is "IS" or Coated Insul-Shield Black. This is a 1" thick fiberglass mat or board product used on the surface of the walls in the room primarily, again, to achieve a proper RT60 in the room. Owens-Corning and Knauf make similar products.


"Stud Twang" is a voice inflection found commonly in the vicinity of the Cheyenne Days and Days of '47 rodeos. The medical community suspects there is a cause and effect relationship with large belt buckles.
 
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