# Forum Home Renovation Home Theatres  Wall acoustic dampening

## shlape

Hi, 
This is my first post here. 
I'm hoping to get some acoustic sealing tips and ideas as I'm currently preparing to remove the placterboard on the adjoining wall with my neighbours in this townhouse complex. From what I've gathered so far I hear neighbour noise in townhouses is all-too-common. 
I've had some advice so far but would feel more comfortable taking the plasterboard down having a solid plan finalised. 
I look forward to hearing from you.

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## phild01

Best to provide additional information about the existing wall structure.  Being a townhouse, it would be expected that your wall would be doubled and heavily lined already.  What type of sounds are disturbing you at the moment?

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## OBBob

Do you know exactly what the current construction of the wall is? This is a tough area with a  bit of black magic involved from what I can tell.

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## shlape

Thanks for your replies phild01 and OBBob. 
The noise problem exists at approximately the 60-140Hz range (according to an app I have on my phone), or what I understand as 'strike noise'. Most I have talked to speak of doom and gloom when it comes to screening bass noise, speaking of it 'travelling through the structure' and there's nothing I can do about it. 
The following is a building report picture of the cross section of my townhouse. The roof and building is continuous but the framework is not.   
I have already tried some simple things. Looking at the picture, the dots represent the aluminium L-brackets bracing the wall. The red dots are the resilmounts I used to replace those L-brackets in the hope they would prevent a noise transmission path, which unfortunately did next to nothing. Considering the broader picture I'm not surprised but I think they may still play a part.
The blue dots are brackets I _think_ are there. I believe I may have just caught sight of the top ones but can't confirm the others which may run the length of the perimeter. When I get to taking the plasterboard off "BED 1" as labeled in the picture, I'll be able to get a better view of the side of the partywall and any flanking paths there. 
These brackets are on both sides of the fireproof partywall; the ideal sound transmission path.  :Annoyed:  
I bought a cheap 4 meter piece of round electrical conduit so I could poke around in the gap between this partywall/firewall and my house's framework. In short, the conduit hit nothing. There are no brackets or hard connectors below the red dots and between the blue dots of the picture above. 
This lead me to believe the firewall may be acting like a huge bass speaker cone. Without any central bracing it may be contributing to resonance between our walls, effectively amplifying the bass noise. 
The bass noises are mainly from the front/rear doors closing, BIR sliding doors closing and heel strike. Hitting the walls with the side of your fist is like hitting a big bass drum. This place was really made 'on the cheap' and I think the existing plasterboard is no longer completely secure to the studs, and it's only about 6 years old! ... but I won't rant about the dodgy builder. 
Measurements I took are below: https://drive.google.com/open?id=0B-...kVETXdGUGRJY1U https://drive.google.com/open?id=0B-...kJHZXJodHNzZkk 
I'm sure flanking paths are a problem as well, as can be seen below. This is why I can hear chopping noises in their kitchen and high-heels hitting the tiling (in their townhouse). I've already started by sealing up these holes with acoustic/fire sealant in the roof (the place I can currently access). https://drive.google.com/open?id=0B-...mR4R0E1U3VnVVk 
I had an 'out there' idea to use EVA foam (and silicone) to brace the firewall but also absorb the noise transmission as can be seen below. I'd be interested to hear thoughts on this. I understand EVA foam isn't fireproof but I've been told (as part of a standard partywall installation) the aluminum L-brackets are designed to fail and let the firewall fall away in the event of complete fire damage. This idea may not be 'up to code' but there's a lot about this place 'not to code' courtesy of my dodgy builder.  :Annoyed:  https://drive.google.com/open?id=0B-...EdKTGtxRFA5bmM 
Before I go ripping the plasterboard off (starting in BED 1, the master bedroom) I need to determine what thickness acoustic batts to use. Using a stud finder I have determined the width needed. Obviously the ticker the better? From the links above you can see the woodwork isn't that wide and I'm concerned of the acoustic batt overhang into the cavity space using 110mm thick batts (R3.1). Do you think this would be a problem? 
I was considering using reilmounts and furring channels mounted on the framework then 13mm soundchek on top of that. This would be done on the adjoining wall where I can here the strike noise coming though. Another question comes from that... what about the other walls coming off this adjoining wall, ie the other 2 walls of the master bedroom? Do I do the same to them? My thinking is, after the soundproofing work is done, the framework near the partywall will still be exposed to the bass noise and could potentially travel through the structure, effectively making it a kind of flanking path around the 13mm soundchek'd wall. Thoughts on this? 
Let just say I'm itching to tear the plasterboard off and make a start, but I'd like to have (at least) the batts, resilmounts and furring channel on hand at that time. 
What do you think?

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## OBBob

Wowser... so you've been thinking about this for a while then.   :Biggrin:

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## shlape

It's been many-a-year in the contemplation/planning.
Many many stories to tell.  
BTW the pics are from within the roof area, and when I say 'not exactly to code', well... have a look what the original build resulted in with the "fire proof wall" https://drive.google.com/open?id=0B-...HdlR0NMSEpvSlU https://drive.google.com/open?id=0B-...U9xQndHakZvenM 
This 'slight breech' has since been repaired.

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## OBBob

Thus is beyond my knowledge to be honest... but you sound like you are on to any air gaps and that's one really important thing to address. Good luck.

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## pharmaboy2

Don't stuff heaps of insulation in to the wall - it just increases the chances of a coupled wall.  90mm wall, 70mm thick insulation. 
green glue.  That's your best chance of fixing bass frequencies without a concrete block wall.  Means 2 sheets of gyprock plus a maybe a $1k worth of green glue for the entire party wall.  Don't skimp on the sheet rock, maybe 13mm fyrchek, then green glue, then 16mm fyrcheck.  Caulk with fire/acoustic sealant. Check their reports on the US site to see if resilient mounts helps for your frequencies , I suspect not. 
once you have done that, if it's not fixed, you know for certain that it's not the wall that is your problem. 
make sure you run some sort of similar system up into the roof space on the party wall, or put another layer of fyrcheck on your ceiling. 
fyrchek is going o help, because if in doubt, add mass. 
oh, the other option for inside the ceiling space, is get mass loaded vinyl - attach it to the rafters as high as you can and let it hang down and lay on the ceiling - you need some overlap on the sides.  
There will be somewhere a direct connection between their floor and the party wall which is transferring footfall.  The joist should be parallel and I'd bet it's side bolted, so you have to stop the noise on your side as best you can.   
Because of of the frequency as I'm sure you've figured out, air flanking isn't likely to be your problem, it's coupling.  I Built a wall a few years ago with ply, then 13mm fyrcheck, batten, mass loaded vinyl and some rubber between batten and frame . You can hit that wall with hammer, and there is not much noise from the hammer and none inside.  It's solvable, start with the party wall first, fix it, then move on to next most likely  
admire your efforts in educating yourself - you are 80% of the way there  http://www.ultrafonic.com.au/Shop/ca...g-Compound.htm

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## phild01

As pharma mentions, it seems to me your primary concern would be coupling.  Particularly that you hear sliding/opening doors and heel noise.  It may be that the construction method is not totally isolated. Could be there is not much you can do that is viable, so be careful how much you spend on the wall dampening.  If you don't hear conversation or TV sound then the wall may be adequate.  Bass sounds are hard to isolate, think about how when waiting for a movie at the cinema and you hear muffled bass from the present movie playing, or when a neighbour is playing music and all you hear is boomf. 
First thing though is to be certain that you aren't being oversensitive to low level sound.  Of course this type of sound can be disturbing to sleep.

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## shlape

Thanks OBBob.   

> Don't stuff heaps of insulation in to the wall - it just increases the chances of a coupled wall.  90mm wall, 70mm thick insulation.

  OK I'll keep the batts within the width of the woodwork. At least it'll be cheaper.  :Smilie:    

> green glue.  That's your best chance of fixing bass frequencies without a concrete block wall.  Means 2 sheets of gyprock plus a maybe a $1k worth of green glue for the entire party wall.  Don't skimp on the sheet rock, maybe 13mm fyrchek, then green glue, then 16mm fyrcheck.  Caulk with fire/acoustic sealant. Check their reports on the US site to see if resilient mounts helps for your frequencies , I suspect not.

  I haven't sourced green glue yet. It's likely I'll be buying that online. 
When shopping around for batts I asked about fyrchek vs soundchek. I was told soundchek is heavier, so I'm thinking "heavier" = "more mass" = "less noise coming through". How much more effective they are is the question. If negligable I'd rather go fyrchek which I think is cheaper. As I've been told, anything that has an 'acoustic' brand to it has a mark-up in price.  :Annoyed:    

> make sure you run some sort of similar system up into the roof space on the party wall, or put another layer of fyrcheck on your ceiling.
> fyrchek is going o help, because if in doubt, add mass.

  I was considering fixing fyrchek to the existing firewall/partywall. Would this be a good idea (in terms of adding mass) to dampen the bass noise. If so, what's the best way to secure it to the partywall? I've seen a bit of that broken off partywall... it's like concrete.
Another 'out there' idea was to carefully remove the existing plasterboard and fix it to the partywall to add the mass. It would only be 10mm as opposed to 13mm ...just a thought.   

> oh, the other option for inside the ceiling space, is get mass loaded vinyl - attach it to the rafters as high as you can and let it hang down and lay on the ceiling - you need some overlap on the sides.

  Would that lay over the insulation batts inside the roof? Aren't they suppose to have ample airflow to avoid mould forming? What if (instead) they were hung down in the cavity space between the partywall and the frame of my house from the top floor roof cavity?   

> There will be somewhere a direct connection between their floor and the party wall which is transferring footfall.  The joist should be parallel and I'd bet it's side bolted, so you have to stop the noise on your side as best you can.

  As mentioned, I put a 4 metre conduit pipe in the gap between the framework of my place and the party wall. Moving left to right I found no coupling, no brackets, nothing connecting physically. This pipe went past the first level floor so I can confidently say our first floors are not physically connected.
The only coupling is the colorbond roof and suporting beams, the front and rear brickwork, and the concrete slab.   

> I Built a wall a few years ago with ply, then 13mm fyrcheck, batten, mass loaded vinyl and some rubber between batten and frame . You can hit that wall with hammer, and there is not much noise from the hammer and none inside.

  I'd be interested to know what type of rubber was used between batten and frame, ie neoprene, eva? 
Thanks for your comments & suggestions. It has given me some more 'food for thought' before kick-starting the project.

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## shlape

> ...Of course this type of sound can be disturbing to sleep.

  Bingo! It's mainly to help with getting a good night's sleep. At the moment I'm relying on a white-noise generator to drown out the noise... not a preferable solution but a short-term one nonetheless. 
Having the sound of someone punching the wall when otherwise quiet... well you'd have to sleep like the dead to get past that. 
...that I can't do.

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## phild01

You mention running conduit in the wall cavity, but other aspects of the construction might be unitary! 
Also, has the neighbour laid a new hard floor surface.  This type of thing is normally governed by body corporate's.

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## pharmaboy2

> Thanks OBBob.   
> OK I'll keep the batts within the width of the woodwork. At least it'll be cheaper.    
> I haven't sourced green glue yet. It's likely I'll be buying that online. 
> When shopping around for batts I asked about fyrchek vs soundchek. I was told soundchek is heavier, so I'm thinking "heavier" = "more mass" = "less noise coming through". How much more effective they are is the question. If negligable I'd rather go fyrchek which I think is cheaper. As I've been told, anything that has an 'acoustic' brand to it has a mark-up in price.   Last I checked, weight was very close, price not so much, but it could have change in the last few years 
> I was considering fixing fyrchek to the existing firewall/partywall. Would this be a good idea (in terms of adding mass) to dampen the bass noise. If so, what's the best way to secure it to the partywall? I've seen a bit of that broken off partywall... it's like concrete. dnt secure it to the party wall, you must decouple whenever you can- if you must, then that's when you use resilient channels
> Another 'out there' idea was to carefully remove the existing plasterboard and fix it to the partywall to add the mass. It would only be 10mm as opposed to 13mm ...just a thought.  It all helps, but it will be more work than it's worth for the dollars you save (10mm green glue 10mm is pretty damn effective as long as there is insulation in the cavity between   
> Would that lay over the insulation batts inside the roof?no, let it drape down to the top of the ceiling, you'll have to look up how MLV works - it needs to be limp and it needs to be overlapped Aren't they suppose to have ample airflow to avoid mould forming? What if (instead) they were hung down in the cavity space between the partywall and the frame of my house from the top floor roof cavity?  If you are allowed to and can - this could be an effective idea - need to check the frequency absorption of MLV though .  I mentioned the green glue because it has exceptional dampening at low frequencies for its weight, not sure on how it compares to MLV , I only used MLV because it was attainable and green glue was not (9 years ago)   
> As mentioned, I put a 4 metre conduit pipe in the gap between the framework of my place and the party wall. Moving left to right I found no coupling, no brackets, nothing connecting physically. This pipe went past the first level floor so I can confidently say our first floors are not physically connected.
> The only coupling is the colorbond roof and suporting beams, the front and rear brickwork, and the concrete slab.   
> ...

  Best of luck, isolating exactly where sound is coming from is difficult.

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## OBBob

Ok, I said above that I don't know what I'm talking about here  :Smilie:  ... but is there any value in less invasive options? I'm thinking like the noise deadening hangings they use in theatres or a really thick heavy woven hanging across a large area of the wall ... perhaps even similar things that could be done to the ceiling? 
Edit ... or ask your neighbour if you could donate them a hanging for their side!!  :Smilie:

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## shlape

'Less invasive' would be preferable but I don't think it'll work. 
Basically I'm addressing strike noise which is a hard-to-solve problem with buildings like apartments. Hopefully, from what I found so far I may not have a similar problem. 
In most parts of the house I can 'roughly' identify the direction of the noise as coming from the master bedroom's partywall, however if I'm standing in the master bedroom it's hard to narrow it down to whether it's coming through the floor or wall.
The strike noise happens through the adjoining master bedroom partywall. I don't know what they're up to in there and I kind of don't want to know if it involves that sort of random noise.  :Wink 1:  Jokingly, I described it to someone as "it's like they're playing a game of catch with a medicine ball, very poorly". 
I have raised this with them on a number of occasion but they claim they're not doing anything that would produce such a noise. I'll give them the benefit of the doubt and consider the theory I heard of 'bass amplification' in the poorly-designed/constructed party wall system. 
I'm building the budget at the moment. Can anyone suggest websites which compare acoustic specs of various batts and plasterboard? I'll do a bit of searching myself but it'd be handy to know if anyone knows of a good one. 
Thanks.

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## chalkyt

You might like to look at a product called "Wavebar". We had it installed in a factory to reduce the factory noise in a drawing office many years ago. It was mostly low frequency rumblings from air compressors and the like and the wavebar was very effective. 
I subsequently used it in an accommodation business that we bought. Originally you could hear whatever was happening in the guest rooms... eeek!!! We relined the rooms using wavebar under the wall lining and it made a heap of difference. 
Wavebar is literally as heavy as lead, and I guess works the same way. My first attempt at using it by myself was abandoned until I could get a "helper". I imagined that I would just hang it like wallpaper... wrong, I could only lift it halfway up the wall by myself! 
So, subject to some advice from the suppliers, you might find that it kills the sound transmission as hanging it on the offending wall should give you a complete barrier with no solid transmission path (except for a few screws or nails). Then, just reline the wall over the wavebar... or be really clever and batten the wall so that you have an extra air space between the wavebar and the lining. 
Good luck!

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## chalkyt

Whoops... forgot to mention that we also put sound bats between the studs when we stripped the lining. They were a green poly material, not fibreglass and tough as anything to cut but the combination worked (just don't know how much was due to the bats and how much was due to the wavebar.

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## phild01

I used acoustica &#124; QuietWave® drywall acoustic barrier product when I did my party wall, in addition to sound and thermal insulation, double stud walls, one being steel framed, and 16mm fyrchek both sides in addition to what was there. 
The Quietwave product, too, is heavy but did manage to unroll it up a 3.6m wall, but only just. 
The total result is good but loud subwoofer movie sounds can still penetrate, though not annoyingly so.  Very loud speech can be perceived in bits. 
There would be some flanking noise too difficult to eliminate and transmission noise as not all the framing members could be isolated.  Overall I am happy with the result.

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## phild01

> Whoops... forgot to mention that we also put sound bats between the studs when we stripped the lining. They were a green poly material, not fibreglass and tough as anything to cut but the combination worked (just don't know how much was due to the bats and how much was due to the wavebar.

   I used that green stuff as well but also Tontine sound insulation which was totally different and IMO better!  That green stuff is horrible to cut.

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## shlape

> I used that green stuff as well but also Tontine sound insulation ...

  They sound a bit like CSR's "Martini Absorb" which I've been told is different to the Bradford Acoustic batts. They claim they're "Thermally bonded polyester fibre". 
I have some acoustic performance figures for them but still looking for the Bradford ones to compare against. It'll be a cost vs effectiveness thing, ie why fork out for something that will marginally provide better performance.

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## shlape

> You might like to look at a product called "Wavebar". We had it installed in a factory to reduce the factory noise in a drawing office many years ago. It was mostly low frequency rumblings from air compressors and the like and the wavebar was very effective.

  Pharmaboy2 suggested something similar. A website I found on Wavebar suggested it could be used "inside cavities". I think I'm leaning toward something like that using Pharmaboy's suggested application of it. 
The thing that is holding me back from starting is deciding what to do about the (centrally) unsupported firewall between our townhouses, which is only bracketed around the edges. I'm happy to be corrected on this, but wouldn't such a large, mainly-unsupported structure vibrate when subjected to low frequencies? Using reilmounts to provide support may help but I'm concerned I'll be adding low frequency transmission paths. Can mass loaded vinyl (MLV) replace the need for this? 
I'll need to price the MLV and was considering hanging it down (loosely) between the firewall and framing/batts of my place from the highest point in the roof. I'm not sure if this will be effective just hanging half way down the wall cavity, and covering the entire wall cavity with this stuff seems like it'll get pricey real fast.  :Frown:  
Considering the cavity area has no obstructions I may be able to add this later if required. Firstly I could add the batts and soundchek, then see how that goes? Alternatively would it be worth starting with the MLV, see if it improves things, then if need-be rip the plasterboard down and add the batts?

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## pharmaboy2

MLV won't be effective doing half the cavity (nothing will really).  If you really have no connections between the stud wall and the party dividing wall, being able to fix at the top and drop MLV down the cavity till it touches the floor is going to be the cheapest option.  Just because buying some plasterboard seems cheap, you have to then apply t, set it, undercoat then paint it - that's no small task and many days labour. 
no matter what, you are looking at some thousands of dollars - it's a lot cheaper than the $50k it costs to sell up and move because you aren't happy.  You have a relatively low frequency problem, you need dampening and there are no shortcuts for that unfortunately - green glue plus multi heavy sheets of PB with insulation or MLV if it will install down the cavity. 
You need mass and mass that won't vibrate .  
Its ts the most annoying thing about BCA and councils, they care about the 1 in a thousand chance your next door neighbours house burns down, but don't care about the certainty that your next door neighbour will make noise that disturbs you.

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## shlape

> Its ts the most annoying thing about BCA and councils, they care about the 1 in a thousand chance your next door neighbours house burns down, but don't care about the certainty that your next door neighbour will make noise that disturbs you.

  Yes... I have entirely different story to tell about this house's builder and their lack of understanding of the BCA. I've been told a number of times it should have been a brick separation, but I have to work with what I have. 
I'm not trying 'go on the cheap' with this, but rather make sure I don't blow out the budget going overboard with things that may not work. 
I'll get some prices on MLV to begin with. It would be great if I wouldn't need to take any other part of the adjoining wall off, ie other adjoining room and ground floor. 
Thanks for all who suggested MLV. I wasn't aware of it (being used for acoustic screening) before coming to this forum.

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## joynz

Have you considered getting some professional advice about this from some one whose job it is?

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## pharmaboy2

I have a mate who was an acoustic engineer - he is deaf, true story. 
fair call though, $1000 might make sure what you do is the right thing for the problem

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## FrodoOne

> You might like to look at a product called "Wavebar". We had it installed in a factory to reduce the factory noise in a drawing office many years ago. It was mostly low frequency rumblings from air compressors and the like and the wavebar was very effective. 
> I subsequently used it in an accommodation business that we bought. Originally you could hear whatever was happening in the guest rooms... eeek!!! We relined the rooms using wavebar under the wall lining and it made a heap of difference. 
> Wavebar is literally as heavy as lead, and I guess works the same way. My first attempt at using it by myself was abandoned until I could get a "helper". I imagined that I would just hang it like wallpaper... wrong, I could only lift it halfway up the wall by myself! 
> So, subject to some advice from the suppliers, you might find that it kills the sound transmission as hanging it on the offending wall should give you a complete barrier with no solid transmission path (except for a few screws or nails). Then, just reline the wall over the wavebar... or be really clever and batten the wall so that you have an extra air space between the wavebar and the lining. 
> Good luck!

  Looking at your problem I was thinking (virtually) what was said by "chalkyt". 
The only way to attenuate low frequency noise in a building is to interpose 'MASS" (i,e. Lead sheeting, or similar.) 
He advocated "Wavebar" and said 
"Wavebar is literally as heavy as lead" 
So, there is your (quite expensive) answer.

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## shlape

> Have you considered getting some professional advice about this from some one whose job it is?

  I tried speaking with people in this line of work with very limited success.
The majority never returned calls or emails, which lead me to think I wasn't enough of a "$$ big ticket item $$". 
I had someone come to have a look and suggest some possibilities. They didn't sound optimistic suggesting the possibility of a room within a room, and that I couldn't expect to get rid of the noise completely.
He mentioned nothing about wall cavity resonance or MLV, and didn't discuss what he could offer as a service. I tried following up with him about the room within a room for pricing but I got no response.
Another company in Sydney suggested this "sound absorbing" system, from what I understand it has some free moving mechanism absorbing the low frequencies. Again, I got no further communications with them, and I'm really not sure if that method would be the way to go, ie possibly too bulky for the space available in the wall.
As you can see, not many willing people in the industry... it would seem.

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## shlape

For anyone following this with the idea of doing something similar, I thought I'd share pricing and any other advice I pick up along the way. 
Wavebar 8kg (Approx. 1.4m wide, 5m long) - $69
Martini Absorb acoustic HD75 insulation (2400mm x 1200mm x 750mm) - $130 (4 sheets per pack) 
The top plate is approx 700-800mm wide and the next (thickness) size up in martini is HD100 (too wide).
The "Acoustic performance" between HD75, XHD75 and XXHD75 is 0.41, 0.45 and 0.40 respectively at 125Hz (which is the approx. target frequency range I'm addressing). I'm assuming higher is better here and the figures don't seem to have much between. The HD75 seems to out-perform the other 75's at most higher frequencies. 
The advice I got from the sales rep was wavebar doesn't need to be secured to the sides. Just the top and sealing around any obstacles along the way down. 
I was in contact with Pyrotek today and was told one of their tech's would call back to discuss this idea. Not-surprisingly I got no call back, but there's always tomorrow... I live in hope.  :Rolleyes:  
I agree with earlier posts that speaking with an acoustic engineer would be a better way forward, but getting people to call back or answer questions seems far too difficult. 
Considering the idea of running the wavebar from the top story roof trusses all the way to the ground I'd need approx 8-10 rolls; maybe the full 10 considering it is approx. 5 metres from the first floor top plate to the ground floor. I'm assuming the best result would be to hang it up at the highest point below the colorbond, or would the top plate be enough?

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## pharmaboy2

Cut a length that will make top plate all the way down to the floor plus 50mm, then cut to size the bit from the rafters down with a 200mm overlap on the other.  It's heavy, and not fun at all to work with anymore than you absolutely have to

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## shlape

> Cut a length that will make top plate all the way down to the floor plus 50mm, then cut to size the bit from the rafters down with a 200mm overlap on the other.  It's heavy, and not fun at all to work with anymore than you absolutely have to

  OK sounds like a plan for the wavebar. 
Going back to your earlier post regarding green glue, I originally thought of using furring channel and mounting the plasterboard onto that. Alternatively, would 2 fyrchek boards (13mm + 16mm) green-glued together be better?
I've heard a suggestion of 2 green-glued boards over a furring channel arrangement but I'm concerned about how much space will be swallowed up. The concern is for the built in robe which (one side) anchors on the shared wall.

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## pharmaboy2

Hi,  check the website for green glue in the US, they have heaps of different test results and equivalencies. I mentioned it originally because it has some performance in the frequency bands you are talking about beyond simply mass.  I've always thought of resilient mounts being good for mid frequency and vibration, the STC ratings etc aren't necessarily useful for you because you have a specific frequency problem. 
if you can get that MLV all the way down to the floor with some overlap, I think it's got a good chance of fixing it on its own, but you are going to need a mirror and focused torch to get a good look down there.

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## phild01

How effective will MLV be if it is only unrolled with open-ended sides!

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## pharmaboy2

You overlap it between each length phil - good question though, it's purpose isn't to solve flanking, but to absorb and muffle lower frequency sounds that travel straight through most other building materials. 
this is why sound is such a inexact problem to solve - hard to locate exactly where it's coming from and thus what will solve it.  Probably why one of the acoustic guys wanted to build a room within a room - it always works, it's just hell expensive and uses up a lot of real estate.

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## phild01

Yeah, I asked the question as there should be a frequency where the flanking issue becomes critical, even though overlapped.

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## shlape

> You overlap it between each length...

  That's what the plan was although it will be tricky getting it down the wall. 
As an update, I spoke with an acoustic engineer who basically told me to 'hit the brakes on the project (for now) and instead start by looking at CSR's redbook to identify the partywall system I have in place (or at least try to identify which one in that document). 
The closest match is the "Timber Frame Internal Wall Systems Party Wall with 41mm Fire Barrier" (pg 12), although I'm pretty sure my dodgy builder did not put the necessary 2x10mm Gyprock Plus plasterboard. I think I'm lucky to get one 10mm standard plasterboard. There's plenty of opportunity for flanking paths as the ceiling plasterboard doesn't quite meet the wall. The cornice makes up the short-fall. Like I said... dodgy. 
The redbook document identifies this partywall as discontinuous which is a good start. Page 36 discusses what I believe to be flanking paths for this partywall system.  
Looking at the diagram my place is to the left with the H-channel supporting the partywall. The neighbour has the attached fyrchek which doesn't go all the way to the roof (parallel with the top plate, approx. 10cm from the apex of the colorbond). I'm glad to see dodgy builder has our fire safety in their best interests. 
I know this because I could see the fyrchek through near the H-channel  they damaged when one of dodgy-builder's knuckle-draggers slammed the roof support  onto the firewall.  :Annoyed:  You can just see it through the hole in this picture: https://drive.google.com/open?id=0B-...U9xQndHakZvenM 
Considering the flanking path (on pg 36) is a 'known issue' with the system, I'll discuss the MLV with the acoustic engineer as one part of the whole solution.

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## shlape

I had a chat with the acoustic engineer again today. 
He basically said to add MLV to the existing wall and then add 16mm fyrchek to the top. This should alter the resonance characteristics of the partywall system but it isn't known if (or unlikely) it will eliminate the bass noise. This was my expectation from the start, hoping to maybe drop the frequency to a less-audible level. 
He warned about using furring channel, effectively turning the triple-leaf system I have into an (untested) quadruple-leaf system, potentially worsening the problem. 
He also added, stripping the wall down and changing the batts may only drop the noise by about 1db; not really worth the pain of doing so. From his experience the best effect comes from tackling the issue at the plasterboard, effectively adding mass, which the MLV + 16mm fyrchek would do. Anything more than this would probably not produce any notable increase in sound attenuation, ie poor cost-to-benefit ratio. 
I was advised not to stick the MLV on either side. Just suspend it like curtains before sandwiching it between the fyrchek and existing plasterboard. 
So what do you think?

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## phild01

Sandwiching is what I did as well, and how green glue is done.  I was nearly going to go with greenglue but did not find any performance figures done for many years after it's installation. 
With regard to what you want you may need 3 layers of 16mm fyrchek both sides!  But what's the point if the wall is not the only entry area.

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## shlape

> With regard to what you want you may need 3 layers of 16mm fyrchek both sides!

  At most I was considering 16mm fyrchek + wavebar + 16mm fyrchek, all attached to the existing plasterboard, but the engineer said beyond the MLV + fyrchek you'd probably need something like 12 layers to notice anything more/better. Again it seems a cost-benefit ratio thing. 
This afternoon (while measuring up the wall) I tried hitting the plasterboard with the side of my fist and noticed (visually saw) the brief vibration. The existing plasterboard really isn't doing anything to help keep the bass out. I think just about anything rigid attached to this wall would make a considerable difference. 
Considering this, maybe green gluing the arrangement mentioned above to the existing plasterboard would be the best way forward.

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## pharmaboy2

> I had a chat with the acoustic engineer again today. 
> He basically said to add MLV to the existing wall and then add 16mm fyrchek to the top. This should alter the resonance characteristics of the partywall system but it isn't known if (or unlikely) it will eliminate the bass noise. This was my expectation from the start, hoping to maybe drop the frequency to a less-audible level. 
> He warned about using furring channel, effectively turning the triple-leaf system I have into an (untested) quadruple-leaf system, potentially worsening the problem. 
> He also added, stripping the wall down and changing the batts may only drop the noise by about 1db; not really worth the pain of doing so. From his experience the best effect comes from tackling the issue at the plasterboard, effectively adding mass, which the MLV + 16mm fyrchek would do. Anything more than this would probably not produce any notable increase in sound attenuation, ie poor cost-to-benefit ratio. 
> I was advised not to stick the MLV on either side. Just suspend it like curtains before sandwiching it between the fyrchek and existing plasterboard. 
> So what do you think?

  Sounds to me like you've described the problem and got a pretty good answer. Totally makes sense.

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## shlape

Thanks to everyone who provided input to this topic. 
Now comes the expensive part. I'm going to get all the supplies together (slowly, as my budget allows), and hopefully it leads to success.

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## Gaza

Just read this thread, you haven't removed any of the clips that support the "h" channel / party wall materials

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## shlape

> Just read this thread, you haven't removed any of the clips that support the "h" channel / party wall materials

  I replaced them with resilmounts.

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## Gaza

Potential issue is that the wall system is design that in event of fire on one side the other side supports the fire wall long enough, I am almost sure resilmounts can't take any heat

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## shlape

Maybe so. I've heard other explanations of the partywall system, and that the resilmounts may be 'too strong' for it. Either way I'm aiming to decouple as best as possible and I think they could have done a better job designing this thing, which seems to have completely missed the acoustic separation point. 
The builder of this place hasn't really stuck with the BCA so this modification isn't making it non-compliant... it was already in that state.

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## OBBob

I have just put James Hardie fire insulation in my boundary wall. Wow that stuff is dense... I wonder if it would be helpful on an acoustic basis?

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## shlape

I've only heard of Gyprock Fyrchek. Not sure how that would compare. How much did it cost, what thickness (mm), and the weight (if you have those specs)? 
I was told by the engineer (I spoke with earlier), that the 13mm Soundchek is equivalent to the 16mm Fyrchek due to the density/weight/mass of the two being similar. 
From what I've been told, mass helps with the bass noises.

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## OBBob

It's 90mm to go inside a stud wall and weighs 80kg/m3. I was just thinking it might be a good alternative to standard insulation?

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## OBBob

It's green, dense and ridgid (as insulation goes).

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## phild01

> I've only heard of Gyprock Fyrchek. Not sure how that would compare. How much did it cost, what thickness (mm), and the weight (if you have those specs)? 
> I was told by the engineer (I spoke with earlier), that the 13mm Soundchek is equivalent to the 16mm Fyrchek due to the density/weight/mass of the two being similar. 
> From what I've been told, mass helps with the bass noises.

  Soundcheck comes in 10 and 13mm, Fyrchek comes in 13 and 16mm.  They equate in weight rather than thickness so it comes down to whether 16mm Fyrchek has a significant price advantage over13mm soundcheck, and if the fire rating comes into play.

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## shlape

Sorry, I had my head stuck in "plasterboard thinking" when you were actually talking "insulation batts". 
Originally I was going to strip the wall back and reinstall the existing batts with something like that, but the acoustic engineer suggested I'd probably only get about 1db drop in the bass noise. 
From all the specs I've read on acoustic batts their frequency tests stop at 100Hz. The problem I have ranges from 60-140Hz, and the results they provide have the lowest attenuation at that frequency range.  
With his advice to leave the existing batts in and focus on thickening the wall, I'll just have to hope this pays dividends. 
I think those batts would show the best attenuation in the mid to high frequency range, as long as there's no flanking paths.   

> Soundcheck comes in 10 and 13mm, Fyrchek comes in  13 and 16mm.  They equate in weight rather than thickness so it comes  down to whether 16mm Fyrchek has a significant price advantage over13mm  soundcheck, and if the fire rating comes into play.

  I just had a look at the quote sheet I got from CSR. They have 25mm (600x3000) fyrchek. It might be interesting to get specs on that price it up.

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