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sound proofing just 2 walls?

Discussion in 'Home Cinema Buying & Building' started by Arkham Insane, Apr 17, 2005.

  1. Arkham Insane

    Arkham Insane
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    hi, im going to build a dedicated cinema room in a few months and was wondering about the soundproofing. The room is 3.5m by 4m and the front wall is connected to the next house, the left wall to the rest of our house. The right and back walls to nothing. Is it ok to just soundproof the 2 walls and the floor. What is the cheapest and most effective way of doing this? i need something good as if i raise my voice you can here it next door right now. The stud partition wall with the plaster board and insulation in between seems like a lot of work, but il do it if there is no better way. any help? thanks
     
  2. Gary Lightfoot

    Gary Lightfoot
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    If you don't think the sounds that may leak through the two walls you don't want to soundproof are going to affect anybody, then you can leave them as thay are.

    The cheapest way to make some adequate soundproofing for most audio frequencies is the 4" x 2" stud wall built an inch away from the existing walls, filled with rockwool or similar, and finished off with two layers of plasterboard (glued and screwed). Make sure all edges at the floor, ceiling and walls are sealed with silicon rubber to ensure an air tight seal - where air can go, so can sound. Replace the door with a heavey duty door and seals around all edges including the bottom - you will probably have to fit something along the floor for it to seal against (edging similar to what exists around the door frame already). Fitting a neoprene rubber strip belween the footer and header 4x2 helps too.

    You need mass and isolation to assist soundproofing - the plasterboard is the mass, and the air gap is helping to isolate. The insulation helps with in-wall resonace and some highe frequencies. As your house is physically touching next door, stopping the deep bass will always be very difficult to do. You can place the sub woofer on an isolation platform to help reduce the physical vibrations from transmitting, but there's no guarentee that next door will not hear your bass. You will have greatly reduced the other frequencies above 125hz though.

    A 'room within a room' will be the best option but means mounting a new floor on some form of isolation platform (that doesn't tough the existing walls) and building new walls and ceiling onto the new floor. you will lose a lot of room though - at least a foot in width and depth, as well as floor to ceiling height. You will have achieved a great deal of isolation though.

    I can probably dig out some pictures of how the walls should be built if you need them.

    For other options, you could always try these people: www.rpg-europe.co.uk. They sell products similar to Auralex accoustic stuff and they have some products for sale in the powerbuy section which may be helpfull.

    Gary.
     
  3. Arkham Insane

    Arkham Insane
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    thanks for the reply, yes the sound leak through the other 2 walls will not be a problem to anyone (except maybe the squirrels outside) , if i have to build an extra platform to further isolate the sound on the floor then this is also something i have to consider. I have read the basic idea of mounting the 4 x 2 wood in a criss cross way an inch from the existing wall and then filling with insulation (you mention rockwool, is this the best because it is the most dense) however i am not at all confident i could do this yet without some more reading. pics would be appreciated. also, how exactly is the wood fixed together and to the floor and ceiling without touching the exisitin wall? cheers, look forward to the pics
     
  4. Gary Lightfoot

    Gary Lightfoot
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    Hi Bepin,

    I'll try to get the pics posted here. Here's a link that might help:

    http://www.audioholics.com/techtips/roomacoustics/SoundIsolationNoise.php

    Here's a pic of a side view including a suspended floor. I think you can use Wickes High Density 30mm slabs for the floor and place your new flooring on top - a floor of 4x2 joists just like a normal wooden floor has, with floorboards on top of that. Make sure the new floor is spaced 1" away from the existing walls - you can probably use Wickes 30mm slabs cut down to do this. The drawing shows a 1" spacer in place. Ordinary rockwool insulation like that used for lofts is often used and is readily available.

    If you want to use extra materials such as soundboard or use something more dedicated to isolating a new floor, talk to Matt who seems to sell stuff for this very purpose. They have a web-site here: www.rpg-europe.co.uk

    Gary.
     

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  5. Gary Lightfoot

    Gary Lightfoot
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  6. Arkham Insane

    Arkham Insane
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    hey thanks a lot, thats really useful, im getting an idea of how to do it now, it doesn't seem as difficult as i thought building another wall might be. the animation demonstrates the steps well. When you say dont use the resilient channel do you mean the resilient bars used, should i just use 4x2 accross instead? i appreciate all the info, thanks! im prob going to start in june so il be getting ready.
     
  7. Gary Lightfoot

    Gary Lightfoot
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    Hi Bepin,

    Resiliant channel is fantastic at isolating a room, but it has one possible drawback that may or may not present itself once the room is finished - they can sometimes convert the walls into a huge bass trap, and no amount of subwoofers will generate any bass in the room.

    I heard of one installation that had resiliant channel and 5 subwoofers but no bass. The walls had to be ripped down and the RC removed. When the walls were re-finished without the RC, a single subwoofer was able to supply plenty of bass.

    Use 4 x 2 or even 6 x 2 if you want better results, but it depends on how much space you're willing to lose.

    If you do go for the new floor, you won't necessarily need to use a neoprene rubber strip between the 4x2 'footer' which you screw onto the floor for the uprights to fix to. You will need it to go between the 'header' which will fix to the ceiling though. Fix 4x2 vertical beams at 600mm centers so the plasterboard edges can be glued and screwed to them. Cross bracing between the 4x2s is used to help make them more rigid. Fit insulation between the beams and make sure it goues to the back wall, as it helps to act as a fire barrier.

    Fit the first layer using no more nails and a few screws. The more screws you use the more of a direct path you provide, so use just enough to ensure a good fixing, but allow for the glue to be the main bonding agent. Seal the joins uisng scrim tape and plaster. When fitting the second layer of plasterboard, make sure the joins don't line up with the first layer, as you're trying to minimise any possible direct routes for the sound to travel through. Use plenty of no more nails to adhere the first layer to the second, so spread it around using the caulking gun to make lots of large 'Z' shapes on the first layer before placing the second layer and screwing into place.

    Try to keep the plasterboard from directly touching the floor and ceiling, leaving a small gap. That will be filled when you use silicon rubber to seal all joins at the walls floor and ceiling. You need to do this to ensure there are no gaps that sound can travel through.

    You can replace the door with a heavy duty wooden door which will help reduce sound travel much better than a normal internal hollow door. You will have to ensure it seals all round with no air gaps, including no keyhole. There are some good methods of sealing doors using rubber beads but I can't find the links right now. I'll try to find them for you though.

    I've enclosed a pic which is a view from above showing the wall construction, but I think you've probably got the idea know from the animation in the other link.
     

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  8. Arkham Insane

    Arkham Insane
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    wow, thanks, that is as clear as it gets. i didnt think about the sound travelling through the screws, i was going to screw it all but il use mostly no more nails now. i feel a bit bad for sacrificing so much space but i guess its worth it rather than the neighbours constantly ringing our doorbell. you've been more than helpful, thanks a lot!
     
  9. Gary Lightfoot

    Gary Lightfoot
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    I used quite a few screws with mine, as I didn't think about the fixings when I did my walls. It wasn't until afterwards that I read some articles that mention using fewer screws along with a glue that I could see the idea behind it.

    There are probably other methods that use rubber washes or similar to further isolate the fixings and help reduce sound travel, but it's dependant on how far you can go and the availaibility of crtain products. Soundboard is something that is similar to plasterboard but is denser so better for soundproofing. Some recommend sandwhiching it between two layers of plasterboard, and some use it as the first layer. It depends on how far you want to go.

    I agree that if you want to keep the neighbours at bay you have to make sacrifices, and it's good to know that people like yourself are willing to do that. There are so many people that turn their music up with no thought or care about their neighbours.

    If you need any more help or pics, let me know and I'll see what I can find.

    Gary.
     
  10. Arkham Insane

    Arkham Insane
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    willdo, should be fine for now, just doing some research into the area. Going to start implementing my cinema in june, after the exams(im a student). will def post some messages later on as i will no doubt need further help, cheers :thumbsup:
     
  11. NoiseStopSystem

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    Just remember that isolation and increase of mass is the key to getting good sound reduction!

    :thumbsup:
     

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