Question Advice on soundproofing for imminent Home Theater build

Lord Dawkins

Novice Member
Hi AV Forums,

Firstly, hello! This is my first post, though I have been lingering for some time due to me knowing the timeline for my build start date.

Also, apologies if this is in the wrong place, I ran a search for threads with the soundproofing tags and it seems a lot of them came from here.

The goal of this thread is to pick the mind of other people, who may or may not have done something similar to myself. I ramble on a bit below, but I am trying to give as much information as possible to allow an educated decision and answer to be possible.

The Room

The room I am working with is 3.4m x 3.75m (11.1 feet x 12.3 feet) within an extension. The room is fortunate enough to have 3 external cavity walls, one of which is the original outside wall prior to extension. The remaining wall is a stud wall shared with a bathroom. The floor and ceiling are both of suspended wooden construction.

Limitations
1. The original external wall adjoins the stud wall though there is a door at the corner at which they join. There is only around 30mm of space that I could afford to lose due to the door opening. There is no way that the door can be moved due to the previously mentioned bathroom.

2. There is a window situated along one of the 3.4m walls. We had new windows fitted last year, the glazing is acoustic double glazing, and there are no trickle vents fitted but obviously a possible weak point.

3. Along the same wall is a radiator, due to the way the joists are fitted the radiator pipe is almost level with the joist, limiting my ability to bring the wall out too far. I can come out approximately 35-40mm maybe 45mm but the pipe will need adjusting with a 45degree bend. I do not wish to lift the chipboard floor as I have learned in other parts of the extension that these are glued and nailed down, with glue along the tongues.

Soundproofing Goals

1. The most important of the goals(apart from having a kickass HT room) is to prevent as much sound as is reasonably possible going upwards. Above this room is our master bedroom, I plan to keep the other half happy!

2. Stop as much sound as is reasonably possible from leaking in to the rest of the house.

Plans

Ceiling
- Current plan for this is to install a resilient channel solution, with 200mm of 60kg m/3 of rockwool or similar within the joists. On to this I plan to mount 11mm OSB, 19mm Knauf Plank, Green Glue and finally 15mm BG Sound Bloc. Everything will be sealed with some form of acoustic sealant, likely AC50 or AC95. The OSB is to add a little extra thickness / mass (at a fraction of Ply costs) and also give screws something to bind to if I ever have to fit something to the ceiling (such as a pelmet).

Stud wall (3.4m) - Exactly the same as the ceiling, except for 75mm of insulation.

Solid cavity wall adjoining stud (3.75m) - Due to the limited space I have on this, I was either planning to install as much mass as possible in the form of Knauf Plank and Soundblock, possibly with Green glue in the middle, though I have read articles suggesting the GG is useless in this scenario. This wall has 15mm of Concrete plaster on to the old external cavity wall which I did some calculations on to be around 28kg pm/2. I am not concerned about the noise going through the wall in to the rest of the house, my concern is around sound transmission through the wall to upstairs.

I also contemplated a furring channel straight to the wall with a single layer of some Soundbloc. Whilst this seems to provide some form of decoupling, reading online would suggest this would cause some resonance at somewhere between 200 and 400hz.

Solid cavity wall with window (3.4m) - Due to the radiator and joist issue explained above I was planning to do similar to the wall above, or as mentioned above also a small cavity wall with a furring channel.

Solid cavity wall (TV/projector wall)(3.75m) - This wall is going to have a decoupled stud build in front of it (probably 50mm), with insulation, OSB, Knauf Plank, Green Glue and Soundbloc. I am unsure if a resilient channel is required if the wall is already decoupled? If it will help marginally on top it seems a relatively cost efficient way to add a few more STC points.

Floor - I am not too fussed with the floor, just conscious of preventing most of the flanking noise. The current plan is to use some heavy floor matting from a company (not sure if I can say company names). This will be sealed on all joints and will have a carpet/underlay installed on top of it. The chipboard floor below will also be sealed prior to fitment. I am not concerned about floor height as the hallway has thick hard wood flooring, so is already quite thick.

Door - I plan to either have a thicker, denser door made, or purchase some form of acoustic door along with seals for around the edges and bottom.

Testing beforehand

Before I started to rip the current room apart I had the forethought to perform some testing. Whilst I have no doubt that this carries no scientific significance, it at least gives me a starting point.

Tests - Take sound measurements with calibrated device at several common frequencies. The sound measurements were taken at various points around my house, along with directly outside the window of the room. The source of the noise / frequency was recorded at 100db @ 20cm (very very loud! I would advise ear defenders if you try it)

Locations-
1.
Hallway directly outside the room with door closed
2. Bathroom with door closed and HT room closed
3. Hallway on the stairs
4. Living room, stood next to old external wall
5. Outside the rooms window
6. Upstairs in the master bedroom


upload_2019-6-17_18-44-17.png


upload_2019-6-17_18-49-22.png


As you can see from the results, I have a fairly decent starting point for most of the rooms. The main weakness appears around the lower frequencies. If I had thought a bit more, I would have performed this test at even lower frequencies. I also recall when taking these tests that the 125hz in the bedroom was noticeable shaking the floor. Obviously I never plan to watch films or listen to music at such volumes as it was uncomfortable, but it gives a good idea of the sound loss around the house at the start.

Question

Going by the information I have provided and the testing and results I have done do people have any feedback on the solutions I plan to implement? Ideally I will be placing the order for materials at some point this week but there is no definitive timeline, just my impatience.

Any feedback will be immensely appreciated. This is the first time I have taken on anything of this type, though I have a fair amount of DIY experience from doing up this house.

Thanks!
Sam
 

citywalker

Member
You have done a huge job already, but here's some things I noticed...
Didn't test subwoofer sound territory: 15-80hz. Most problems are related to stopping low frequencys.
Your ideas are great, but without real decoupling whole room (creating room in room) you can't stop low frequencys.
Of course all this helps and you probably can use this room listening little bit louder than before, but don't expect 'kick ass HT room' soundproofing results.
I'm personally not sure, that all this hard work pays off.... at levels what you expect.
 

Lord Dawkins

Novice Member
Hi Citywalker,

Thanks for the reply and sorry fr the sloth like response. I appreciate your feedback on what I wrote.

I am aware that I will not get absolute silence or anywhere near, my goal for sound is to be able to listen to a movie at an enjoyable level in the evening. I may have to turn the sub off once the Mrs goes to bed but I can live with that.

I have purchased all of the ceiling materials and some for the new stud I am going to build, along with the floor, just because I was looking to qualify for free delivery.

The window wall and old external wall are still up in the air. I have seen a few solutions by SoundStop for low profile walls which I might ring them about next week. As I said not looking for fantastic results, but a 10% increase is acceptable in my eyes, just trying to not make it worse.

One solution is SM20 panels with a single layer of plasterboard and the other is with Tecsound 50 with several layers of board.

I would still appreciate any input from anyone if you feel like contributing.

I am contemplating starting a build blog in the DIY section as this is going to take me a few months at least and motivation from people will help :)

Cheers,
Sam
 

Harkon321

Well-known Member
Impressed with what you've already managed.

Bit confusing trying to follow the walls info as it is different for each wall. Can you not frame the room with 2x3 timber, spaced 20mm off the block walls and then rest ceiling joists on top? Or will you lose too much ceiling height? Personally think it's easier than all the faff with channel.
One wall it looks like you've gone all mass but no insulation or isolation. Would think you'll get flanking as it's not decoupled.

I've read up quite a bit on different channels and if you properly decouple the wall, there is no benefit in adding channel.

The mass you're adding sounds great. Wasn't sure what you meant regarding Green Glue not working in some situations? Can you elaborate?
 

Lord Dawkins

Novice Member
Hi Harkon,

Haha yes I did not explain it so well. Thinking about it now, if you refer to the image with the rooms and numbers on (sound test):

4 = Solid cavity wall adjoining stud (3.75m)
5 = Solid cavity wall with window (3.4m)


Unfortunately wall #4 has a clearance issue with the door as described. I have since come across a solution from SoundStop that I am tempted to try out, it involves 2 layers 2 tecsound 50, with a piece of plasterboard in between each piece. I would assume tecsound would offer a small bit of damping which may help with flanking, but I have found nothing to support this :(

Wall #5 also has clearance issues due to the radiator and joist limiting the distance I can bring the wall out, I was planning a similar tecsound solution as the other wall but am always happy to hear other peoples feedback and opinions.

In a perfect world I would be able to do what you suggest with the walls and ceiling, however, such is life, there are compromises we have to make and this is just something I cannot do. I have racked my brain and come up with the best I can achieve.

In reference to my comment about Green Glue, I have read on the net (think it was AVF actually!) that GreenGlue used on plasterboard that is mounted directly to the wall is not a lot of use. I believe it was down to the two materials being of difference stiffness or the like. I am not sure if this extends to plasterboard mounted to plasterboard that is mounted to the wall directly :D
 

Lord Dawkins

Novice Member
These walls are currently finished in plaster, beneath that is concrete plaster (15mm) and beneath that concrete block.

I am contemplating tecsound straight to the wall, then PB, GG and PB, but unsure if the direct to wall (via tecsound) will counter out any green glue effect?

I guess it is all speculation as there is no lab data on any of this. :smashin:
 

Harkon321

Well-known Member
Problem is that you’ve got no isolation or insulation. You’re just adding mass and possibly camping through green glue.

It’ll help sound transfer for sure but it will be massively compromised due you missing the other two. It will help but it’s quite a lot of money to spend. Depends what you’re after really.

I caveat this that I’ve not done mine yet. Ive done my reading on AVS, Soundproofing websites and the recommended book ‘how to build a recording studio’. Can highly recommend it.
 

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