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Hey all,

found this forum while I was starting my HT build and thought I would post here what I am doing, in the hopes that I may get some suggestions and may help some others with their builds.

I live in a 4 bedroom home in Adelaide, Australia.

I have a L shape room that I am converting to my purpose, sectioning the largest portion into a dedicated theater. I have started on a room within a room style theater. I have done a lot of research on sound proofing and room treatment, but am no means an expert.

Construction started this week, installing a double stud wall. Something I have done different to most, is the internal stud wall. It is isolated from the concrete slab using 'Waffle Pad' (a new style) and rubber washers.

The Drywall (what we call Gyprock here in Australia) will be 16mm Fire Rated (5/8") two layers with "Green Glue" between(I am interested if anyone else has had experience with this).

I am looking at a floating floor design to isolate from the concrete slab. And I am looking to sound proof the ceiling.

For those interested, the completed room will have the following internal dimesions 4.9m(L) x 3.3m(W) x 2.4m(H) (16'1" x 10'10" x 7'10").

I am looking for suggestions on how to sound proof the ceiling and any comments on the "Green Glue" product.

Thanks
Dave
 

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Green Glue is a great product. Can't recommend it highly enough.

Floating the walls like this is fine - just understand you still have to fill that gap with something and get some mass in there so you don't defeat the isolation gained. If it were me, I'd just build the walls on top of the floated floor instead of floating the floor in the center of the walls.

To complete the isolation you're planning, you'll need something like PAC International DC-04 isolation clips to tie the wall tops to the structure above instead of directly tying it. You'll also need some sort of clip and channel system (RSIC-1 and hat channel recommended) to isolate the ceiling drywall.

Remember to alternate layers of drywall - ceiling, then 4 walls, then back to ceiling, then 4 walls. Caulk all 90 degree joints. This forces the sound to try to get through a Z shaped 'crack' as opposed to a straight line.

Pay very close attention to ANY holes in the room. Any outlets, can lights, switches, etc. - anything that cuts a hole in your room defeats the isolation.

Bryan
 

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Hi Bryan,

that is what I was thinking of doing, using a resilient mount with channel. I have already put the walls in place, they are isolated top and bottom using rubber so that the bolts do not touch the timber (was thinking of using a steel frame, but much quicker and eaiser to use timber). Thanks for the heads up with the drywall, I have a bit of info from an Australian (but interstate) company who specialise in sound proofing, and they suggested the same technique as you have, as well as recommending green glue. They suggest a fire rated mastic sealant and a box or overlapped section over any penetration/switch/socket.

Dave
 

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I second the green glue comments. it's good stuff - worth the money. first time i've used it but it amazed both myself and the guy that installed my sheetrock. when you knock on the wall - you can't tell where the studs are anymore... the whole wall sounds like it's a stud. :)
 

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Correct. Any holes in the wall for electrical should have a massive (we use MDF) box behind them with just a single hole for the Romex to enter - and that's caulked up. For lighting, due to the heat, the boxes will need to be a bit bigger and you'll want to make sure you use IC rated cans if you're using can lighting.

Bryan
 

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Penetrations for single outlets are demonized. They are not the threat that people perceive. The issue is the size of the penetration opening.

If you have a single outlet box, it simply needs to be sealed up. Acoustic sealant, caulk, putty pad, etc. Some insulation behind it and you're fine. It's not a significant enough opening to worry much about once seales airtight.


Double and triple gang boxes are getting larger, and this now allows a lower frequency problem. This is the same issue when you have recessed can lighting. Typical new construction cans are 6.5-7.5" diameter. Way too big and these are definately worth worrying about. They need the massive backer boxes mentioned.

More of a concern is the ventilation and doors. They are the two biggest sources of flanking.
 

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Agreed on the ventilation and doors. I would respectfully disagree on the outlets and switches. When you look at the sheer number of them in a room, that's a lot of opening. Figure 2 on each wall for outlets. Add in however many switches and you have a pretty decent amount of loss.

It's not hard to box around them and IMO, it's worth the extra 10 minutes per outlet to do.

Bryan
 

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I don't mean to be argumentative. Sorry if I appear that way. I mean no disrespect whatsoever.

It is intuitive that a small opening would unravel all the good efforts of soundproofing. But the data is quite clear that this is not the case at all. Surprising, really.

The NRC studied this exact phenomenon in their excellent study IR-772. Series of outlets were tested and found to have very little to no effect on the resulting STC. We know that due to the small opening, any loss of isolation would be restricted to the higher frequencies.

I myself was involved in similar testing looking at multiple small wall penetrations. As long as the holes were small, the compromise to sound isolation was incredibly small.

Applying massive backer boxes to small outlets sure won't hurt anything, but they have been thoroughly lab tested as unnecessary.
 

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No offense taken. Just good discussion.

Understand on the frequencies issue. IMO, it's still a loss. People spend a lot of time and money trying to get everything sealed up the best they can and I don't want to let something like this compromise it in any way - no matter how small.

If we go by that theory, then there would be no need for any caulking of seams, not letting drywall joints overlap, etc. as those 'openings' are an order of magnitude smaller than an outlet box. How about the gap under a door that's only maybe 1/4"? Sure makes a difference in my book.

Bryan
 

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If we go by that theory, then there would be no need for any caulking of seams, not letting drywall joints overlap, etc. as those 'openings' are an order of magnitude smaller than an outlet box. How about the gap under a door that's only maybe 1/4"? Sure makes a difference in my book.

Bryan
Yes, but those are all examples of unsealed flanking paths. A sealed outlet is sealed.

My point is that everything needs to be sealed, but the heavy backer boxes are not necessary on single gang outlets. Get much bigger than three gang and the backer box becomes necessary.
 

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So you're saying that as long as I caulk the seams of drywall, I can line them up right on top of each other? No need to stagger 90 degree joints?

Sorry - guess we'll have to agree to disagree. Yes - each by itself is a little thing. But, all the little things add up to a big thing. I'm going to keep recommending what I know works for sure. Mass. I know with mass, it's not going to be an issue.

Bryan
 

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I must be just generally dense today. I'm not finding anything on the site showing a direct comparison with outlets not sealed, sealed, and backer-boxed as far as difference in noise transmission. Got a specific link?

Bryan
 

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For those interested, the completed room will have the following internal dimesions 4.9m(L) x 3.3m(W) x 2.4m(H) (16'1" x 10'10" x 7'10").
Hi Dave,

Your room dimensions are almost identical to my own..5m.x 3.2m.x 2.4m.
I'll be following your build with interest..
One thing you will need to include is a lot of acoustic treatments..
Small rooms are notorious for sound reflections..
 

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Discussion Starter #15
I must add that I have only one door to this room and I am in the process of designing an airconditioning/ventilation system for this room, any suggestions on this appreciated.
The door will have a double seal, acheived by attaching a smaller sheet of MDF to the door to give a staggered seal effect. Two doors will be used to give a 'dead air' chamber. This should take care of the door.
 

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Sorry for disrupting your thread.

For HVAC, you want flex duct or duct board. How to isolate it depends on how it will be run. If it's in the soffit and there are no penetrations in the soffit, you're good to go if you have enough length and it's all insulated.

If there are penetrations, you can use a similar type MDF box to hold the ducting. Preferred is at least 3 90 degree bends with at least 5' between them from exit of the room to the diffuser itself.

Bryan
 

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The boxes that are installed in electrical device holes are not of sufficient mass to stop sound from leaking. That is reason enough for me to re-establish the continuity of mass with surrounds made of MDF or some other type of dense material.

I think putty pads are as good an idea for closing penetrations versus nothing.
 

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The boxes that are installed in electrical device holes are not of sufficient mass to stop sound from leaking.
... Surprisingly, this is not so. Data shows that plastic works better than steel, despite the reduces weight (for that sized hole).

If you feel more comfortable installing MDF boxes, that's fine, of course.
 

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But....:)

The typical box has minimum four tabs that allow leakage, even if the plastic has the properties to stop 100% of the sound it encounters. It's stickler notion of mine and others I realize this Ted, but for good reason.

Where I am, code requires a device every six feet(IIRC) from the corner. That can easily translate into a lot of small leaks that add up to a big leak. A small bedroom can have five boxes. You turn that into a big theater that has hvac noise that didn't quite get isolated, leaks in windows that did not get mass matched as well as should be, doors that leak just because the builder is tired of all "this" and, and, and, the additional requirement for devices and switches and cabling passthru, you have a potential isolation leak as big as a small window.

I'm on your side that one receptacle box space may not effect isolation, but where in what room does only one box space exist? Don't you have to consider the cumulative totals? How close together can you install one space boxes and not have them reduce your work?
 
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