Film-Tech Forum ARCHIVE: sound proofing

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Posted by Ben Mozer (Member # 3401) on 10-30-2006, 11:01 AM:

I'm starting a twin theater and will be splitting one big room into two small theaters (80 seater, 50 seater) and am having trouble with the sound proofing problem. my architect says i need to take the dividing sound proof wall all the way to the roof deck or else there will be too much sound transfer. now the ceiling is insulated with R-38 and I'm thinking if i double drywall the ceilings the transfer will be minimum as to not necessitate demoing the existing ceiling and building that wall all the way up, especially sinceall the movies i show will be independent/foreign and not have many loud scenes.

am i crazy?

Posted by Jesse Skeen (Member # 586) on 10-30-2006, 12:34 PM:

Keep the theater the way it is. Twinning is so 70s.

Posted by Ben Mozer (Member # 3401) on 10-30-2006, 01:44 PM:

not really what i'm asking. we don't have much choice in the matter as far as splitting the space. too many pillars

Posted by Kara Tillotson (Member # 3899) on 10-30-2006, 02:57 PM:

Im not sure what else they did but at our theatre, which was originally a single, they put up a bigass cement wall....but then again im not sure what else they put there. But with ours it was just blocking off the balcony to make it a seperate theatre so probably less interference witht he other screen.

Posted by Richard Fowler (Member # 893) on 10-30-2006, 03:07 PM:

The basic problem is low frequency such as part of the male voice or rumbles, thumps ( such as a door closing ) et cetera on the sound track, traveling between rooms. Double drywall in the ceiling will help stiffen but the STC ( sound attentuation factor ) from the extra sheetrock is slight; double drywall improves covering the gaps between the sheets in preventing sound transmission. The trick is to have a floating ceiling with insulation and air to trap the transmission versus going to the roof with your dividing wall; whichever is cost and time effective. In test situations we have produced pink noise @ 85 db minimum level to listen for sound transmission issues between rooms in rehab projects and usually gives the client the point(s) we are addressing.

Posted by Mike Blakesley (Member # 26) on 10-30-2006, 03:16 PM:

Ben: Contact Polson Theatres, www.polsontheatres.com. They are a Montana circuit (24 screens). Probably half of their locations were old singles when they acquired them and they've twinned quite a few of them. The owner (Howard Pickerill) is very good at it and could probably answer your questions, and he absolutely loves to talk shop.

You can get their phone number from the "home" page on their website. Howard is semi-retired and lives part-time in Utah when the weather is cold, but the general manager Gary Dupuis would probably give you his phone number. (And Gary is very knowledgeable, too.)

You can also e-mail them from the site, but they don't check their email very often, so phone is the best way to contact them.

Hope this helps.

Posted by Gordon McLeod (Member # 33) on 10-30-2006, 03:46 PM:

The simple awnser is the demizing wall must go to the roof deck and not be pierced
any other solution will in the long term be found unsatisfactory

Posted by Ben Mozer (Member # 3401) on 10-30-2006, 05:48 PM:

thanks, everyone. i didn't know if i would get any responses, this has been a big help.

Posted by Steve Guttag (Member # 268) on 10-30-2006, 10:48 PM:

I'll go further than that. The demising wall must go from beyond the floor to above the roof.

I've done some FSTC measurmenets and just the fact that the wall behind the screen, the booth wall and the continious slab reduced a wall's STC rating from STC-72 to a mere FSTC of 62. Cutting the slab can not be over emphasized. Sound travels through solids better than through air. Any common surfaces between the rooms WILL be a point of sound transfer. Also, keep all of the air vents away and non-common...they are great for transfering sound.

For non-digital films an STC-65 is about as low as you can go without noticing the sound transfer...for digital it shoots up to at least STC-75.

Posted by Mark Gulbrandsen (Member # 72) on 10-31-2006, 07:49 AM:

quote: Steve Guttag
I've done some FSTC measurmenets and just the fact that the wall behind the screen, the booth wall and the continious slab reduced a wall's STC rating from STC-72 to a mere FSTC of 62. Cutting the slab can not be over emphasized. Sound travels through solids better than through air. Any common surfaces between the rooms WILL be a point of sound transfer. Also, keep all of the air vents away and non-common...they are great for transfering sound.

I agree with Steve but I've also had the larger leakage problem happen from sound traveling down the roof decking. Like he mentioned cutting the floor is a very good way to control leakage along that path, while cutting the roof decking is all but impossible unless the entire roof is removed and rebuilt as seperates. So exploring other alternatives of controling or minimizing leakage along the deck is a very good idea. Roof deck transmission is one of the biggest problems in strip mall type buildings I've encountered. In new construction spliting the floors and roof decks is practical and done all the time.

All of this is very definately best left to an acoustician who deals mainly in theaters to get it right for you.

Mark

Posted by Monte L Fullmer (Member # 2797) on 11-07-2006, 10:10 PM:

Question on cutting the floor: does the floor has to be cut ALL the way through, or down to the foundation gravel, or can it be cut just down enough to limit the sound travel - esp if the floor had ductwork and crawlspaces underneath that can't be cut through..?

Heard also that with using the floating ceiling is to lay thin lead sheets across the top of the wall to the ceiling to prevent sound crossover to the other house...but need corrective info on this one.,.

-Monte