# New basement, new HT, needs advice on soundproofing



## dahak (Mar 9, 2008)

Hello all,

Boy am I glad that I found this forum. I've been reading through it for the past week and even tough I knew that building a dedicated HT would require a lot of planifications, I didn't know it could become that crazy ! So here I am looking for some advice. 

Background of the basement and the HT to be: 
- New home, built in 2006
- House is a semi-detached type (2 units in one physical building with concrete wall between the 2)
- No inside divisions in the basement yet , only the exterior walls are framed with studs and insulated
- Total basement size: 30' x 18' 6" (not huge I know)
- Ceiling : 8'
- the actual budget for the construction of the HT (doesn't include any equipment) : 5000$

I have to say also that unlike most other HT people here, I don't own any HT a/v equipment yet. So yes, I am really starting from scratch. This is why I will be browsing these forums for a very long time, sucking all the knowledge from your brains !!! :hail:


Now since I am in the planification process, I was thinking of asking the experts to prevent costly mistakes. Since I assume most people are visual like me, I have included a Google Sketchup plan . 










The HT room itself would be around 18' x 11'

My first serie of questions will be about soundproofing. Since my wife can get really testy if I watch a movie too loud, I need to make sure that no sound comes out of the HT.And of course, since it is a semi-detached house, I have neighbors right on the other side of that concrete wall.
I've read a little about double studs, staggered studs walls, sound clips, decoupling etc... 

First question: How should I sound proof the 2 walls next to the foundation (concrete walls)?
2nd question: How about the new walls that I will have to build (the front wall and the side wall next to the stairs) 
I also know that I will have to use a soundproof door.I am still hesitating between a drywall celing and a hanging one. I understand that drywall celing gives you a better sound isolation. 

And with this kind of HT size (18' x 11'), do you guys think that I would be able to squeeze two row of seats in there. 

Thanks in advance. 

Yanick
PS. I am including the Google Sketch Up file if some of you really feel like giving me the best possible advice on the design of my HT. 
http://www.nazcasolutions.ca/images/basement2.skp


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## bpape (Sep 14, 2006)

Welcome to the forum.

You can do 2 rows in there, just plan for that first and get a screen sized accordingly. Don't make the mistake of picking a screen size and letting it drive everything else.

For the room, if you're AT ALL concerned about isolation, forget the drop ceiling - not gonna happen. If you do that, you might as well forget clips, staggered studs, solid doors, etc. - because you have a hole the size of the square footage of your room at the top for bass to go through. That's the WORST place since some of the floor structure between units is likely shared.

If you planificate properly, hang all of your walls on DC-04 clips to isolate them. That negates the need for RSIC-1 clips on the walls and saves you a bunch. This lets you do double drywall and green glue to get better isolation. Staggered stud walls on the 2 walls not against the foundation will work - double walls will work better.

Does your $5k budget count seating? Or, is it just the room, electrical, carpet, etc? If you're DIY'ing and it's not seats, you should be able to do a nice job in that budget.

Bryan


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## dahak (Mar 9, 2008)

Hi Bryan, 

The 5K budget does not include seating, it's only for the construction. And yes, most of it will be DIY except for the electrical, one of my neighbor is a commercial electrician and will help me with that. 

As for the ceiling, yeah, that's what I thought... so drywall it is...

When you say double walls, you mean double stud walls like the one showing here ?

And what kind of wall for the 2 against the foundation ? Would the existing single stud frame and insulation be enough since it is sitting against a concrete wall ? I also have 10 4' x 8' sheets of Sonopan that I bought more than 1 year ago. Where could I use it effectively ?

I am also a little bit concerned about my equipment rack. I am not sure if the actual spot where it is on my plan would be OK.

Thanks again for all your help


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## jerome (Apr 24, 2007)

bpape said:


> You can do 2 rows in there, just plan for that first and get a screen sized accordingly. Don't make the mistake of picking a screen size and letting it drive everything else.


This is really important because it could lead you into a difficult situation where you have to place your speakers in from of the screen or sit way too close to a large screen. I have experienced it, unfortunately 

What I recommend is that you work with the acoustics first and find out your screen size later on when your speakers and seats are correctly placed. As Bryan noticed, don't choose a screen size according to your room size and try to make everything else fit to it because it doesn't work very well.


For you door, you may want to consider mounting 2 standard doors instead of an expensive soundproof door. I couldn't do it myself but have read that this solution works fine too.


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## dahak (Mar 9, 2008)

jerome said:


> This is really important because it could lead you into a difficult situation where you have to place your speakers in from of the screen or sit way to close to a large screen. I have experienced it, unfortunately



Make a lot of sense. What is the formula again to calculate the screen size according to the seating distance ? I saw a link to a website with a calculator on the forums but I cannot find it anymore.


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## salvasol (Oct 31, 2006)

dahak said:


> Make a lot of sense. What is the formula again to calculate the screen size according to the seating distance ? I saw a link to a website with a calculator on the forums but I cannot find it anymore.


Here is one http://myhometheater.homestead.com/viewingdistancecalculator.html#anchor_13194

You'll be okay with two rows, my room is 18 x 9 x 8 and I have two ... the viewing distance form first row is around 11', but the only problem is that my second row is just 1' from back wall; so if is possible make your room a little longer than 18' :yes:

By the way, I have a rear projection DLP (18" deep), so if you use a front projector and put your screen against the wall you'll get 3' in the back ... but if you build a stage it will change everything :yes:

You'll have a nice HT ... check this threads you'll get a lot of ideas 

http://www.hometheatershack.com/for...-tanner-ridge-cinema-construction-thread.html 

http://www.hometheatershack.com/for...construction/8587-blaser-ht-build-thread.html 

http://www.hometheatershack.com/for...n-construction/5979-finniss-home-theatre.html


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## dahak (Mar 9, 2008)

Thanks for the links David. 

The Tanner Ridge cinema is quite impressive. I'm really looking into building something similar. I love the idea of having a stage.

It wouldbe almost impossible for me to have the room longer than 18'. 

Can someone tell me what is the minimum distance I should have between my rear wall and the 2nd row seat ?


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## bpape (Sep 14, 2006)

Screen size will be driven by a combination of proper viewing angles and the throw distance/brightness of the PJ that you're considering. We have to do it all together as 1 plan or something suffers.

When I say double drywall, I mean just that. Normal walls but 2 layers of drywall instead of just 1 and with Green Glue between layers. The other thing that must be considered is HVAC and electrical. ANY hole you cut in the shell is a sound leak. Everything must be isolated to do it properly. 

Bryan


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## dahak (Mar 9, 2008)

bpape said:


> Staggered stud walls on the 2 walls not against the foundation will work - double walls will work better.


I was talking about that part ... by double walls you mean double studs wall ?

And what about the 2 walls against the foundation ?


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## gullfo (Nov 25, 2006)

you can use a pair of walls back-to-back, alternating studs on a wide plate, or you can split the plate with a cut and stagger the studs on that. that gives you more isolation than just staggering but not as much as double walls. steel walls can be single wall and get good isolation. it also partly depends on whether or not the walls need to be load bearing or not.


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## dahak (Mar 9, 2008)

Many thanks for all that info Glenn and Bryan. From what you say and from the reports I saw on the Green Glue Company website, it seems double wall would give me the best soundproofing option but of course, I don't have an unlimited budget so I might go with the staggered "cut" solution proposed by Glenn. 

Now excuse my ignorance but what should I do with the 2 walls sitting against the foundation (concrete)? I know that concrete is pretty effective in blocking some frequencies. So my question is can I save some money with these 2 and go with a regular single stud wall option ? Or should I treat it just like the 2 other walls and if so, then why ?

Thanks for all your help. :T


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## bpape (Sep 14, 2006)

No need to do any special framing on the walls close to the foundation since you won't be drywalling the back side. You still need to double the drywall and the Green Glue or sound will find that weak point and flank around it to the upstairs that way.

The split plate wall can work just fine. Part of what the double wall gives you is more depth to the cavity which will also lower the resonant frequency of the structure. Either will work. Just weigh the cost diff of the 2x6 bottom and the labor vs double 2x4's and much easier assembly. If space is at an absolute premium and your time is 'free', then do the split.

Bryan


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## dahak (Mar 9, 2008)

Thanks for the advice Bryan. Can't wait to start building my HT !!!


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## dahak (Mar 9, 2008)

bpape said:


> If you planificate properly, hang all of your walls on DC-04 clips to isolate them. That negates the need for RSIC-1 clips on the walls and saves you a bunch. This lets you do double drywall and green glue to get better isolation.


Are these the clips you are talking about ?

http://www.pac-intl.com/decoupled_lp_wall_systemx2.html


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## bpape (Sep 14, 2006)

http://www.pac-intl.com/decoupled.htm

... though sometimes we have to use them a little differently when there isn't a concrete wall right next to it. You can actually tie the 'tail' of the clip to a joist above, build the wall 1/2" short, and put the rubber pad on the top of the top plate so you get a shearing force across the rubber when the wall tried to move.

Bryan


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## dahak (Mar 9, 2008)

Sounds good. 

Tonight I've verified the space available for my HT project (created temporary divisions to see how much space I need) and I'm happy to say that I should be able to use double stud walls for the 2 walls not sitting against the foundation: 

5/8" drywall + GG + 5/8" drywall + 2 x 4 wood stud with insulation + 1" air gap + 2 x 4 wood stud with insulation + 5/8" drywall + GG + 5/8" drywall (as recommended on the GG website)

For the 2 other walls that are sitting on the foundation, I would use:

5/8" drywall + GG + 5/8" drywall + insulation w/studs attached to DC04 clips in concrete

Does this sound Ok to you Bryan ? 

Since I am not planning to sell this house (not for next 20 years anyway) I think that it would be better to go all the way with the actual construction. I will only have one chance to build it right...


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