Soundproofing question

[gio321]

Hi all,
I'm soundproofing a room (walls and ceiling) and the company I'm getting the materials from suggested the following solution.

Independent stud wall 100mm with 60kg/m3 rw3 rockwool, resilient channel, 19mm sound plank, green glue + tecsound sy50, 12.5mm acoustic plasterboard.

My question is, Is there any benefit from using both the Tecsound panel and the green glue? They are both recommended to be installed between the 2 boards by the manufacturers. Will I get better performance installing both between the boards or will it be worse, since both materials require to be sandwiched between 2 rigid materials? Should I for example install the tecsound between the resilient channel and the 19mm board and then green glue between the panels?

The room will be used for mixed tracking / mixing use and is around 8.5m x 3.5m

Thanks in advance,
George

[Soundman2020]

Hi there George, and Welcome!

the company I'm getting the materials from suggested the following solution.

That would be the first alarm bell and red flag! Maybe I'm just too cynical, but it's rather strange that the company that wants to sell you lots of products is also the company that is recommending that you buy lots of the products that THEY happen to sell! If I were a car salesman, I'm sure I'd be recommending that you buy an expensive car with all the accessories, even if I knew that what you really needed was a motorbike!

Independent stud wall 100mm with 60kg/m3 rw3 rockwool, resilient channel,

Second red flag/alarm bell, and this is a big one. It indicates either ignorance or deliberate intention to sell you what you don't need. If the wall is an "independent stud wall", then why would it also need "resilient channel"? That makes no sense. The purpose of building an independent wall is to have the mass (plasterboard) on one side decoupled from the mass on the other side. That's why we recommend independent walls in the first place! So if the independent wall accomplishes that so well, why would you also need to decouple the wall again, using resilient channel? Answer: you wouldn't! If the wall is already decoupled, then then there is no need to decouple it a second time. There's only two reasons why someone would recommend doing that: 1) they don't have a clue about acoustics, and don't know what they are talking about, or 2) They actually do have a clue, but they wanted sell it to you anyway, to line their pockets at your expense...

You do NOT need resilient channel on an independent wall. That would be like someone telling you that in order to get as wet as possible, you need to go sit on the bottom of the ocean, but you should also take a running hose pipe with you to get you even wetter... It really is that silly. If you are totally wet, then you are totally wet and no amount of extra water is going to make you wetter. If your wall is fully decoupled then it is fully decoupled, and no amount of resilient channel, isolation clips, hat channel, or anything else is going to make it "more" decoupled.

Just for fun, ask them why they think you would need resilient channel on a wall that is already fully decoupled... I'd love to hear their reasoning. Ask them for published test results that support their answer...

Is there any benefit from using both the Tecsound panel and the green glue?

There's a MAJOR benefit to that, yes! It will make them richer and you poorer! Of course, that's not a benefit for YOU... But it sure is for the sales quota of the guy wanting to sell you that. There's no acoustic benefit at all, and in fact I suspect that using both together would be detrimental to isolation. Each manufacturer has tested their product in specific ways, and has specific test results to show how it works when used as intended. But neither has tested both of those together, so there's no results. Green Glue, for example, is a visco-elastic CLD, and as such it is designed to be used between two massive RIGID layers of a walls, such as between two layers of drywall, or drywall and OSB, or MDF and plywood. But Tecsound sy50 is not rigid mass! It is also an elastic polymer! Therefore, Green Glue would NOT be able to work the way it was intended and designed to work, as it would have no "second layer of massive rigid material" on one side! CLD (Constrained Layer Damping) products work by damping acoustic transmission in the sheer plane between two solid surfaces. If it is not in contact with one of those surfaces, then it cannot do its job.

So you are correct: you do not need both of those. In fact, you probably don't need either of them!

will it be worse, since both materials require to be sandwiched between 2 rigid materials?

Exactly. Your suspicions are well founded. Whoever recommended that is either clueless, or out to milk your wallet dry.

Should I for example install the tecsound between the resilient channel and the 19mm board and then green glue between the panels?

Neither! Forget the resilient channel, since you do not need it, and forget the Techsound barrier, since you do not need that either! You could use Green Glue between two layers of drywall (plasterboard), nailed directly to independent studs, yes. That would work. It would be far cheaper, and probably more effective, than the weird and exotic conglomeration sandwich that you were told to use. That's a known and tested method, and it works very well.

Here's the thing: in the equations for calculating low frequency isolation, the only parameters that you can plug in, are the numbers for the mass of the two leaves, the distance between them, and the damping. There's nothing else! Those are the ONLY factors that govern the resonant frequency and the isolation of a two-leaf system. Sound waves cannot read price tags, so they really don't care how much you paid for the mass or damping that goes into your walls. So it makes sense to use the least expensive materials that will do the job. Exotic materials will do the job too, if they have the right mass and damping characteristics, but why pay more? The sound waves don't care... they are totally unimpressed by the cost of the materials... All they react to is the mass and the damping.

The room will be used for mixed tracking / mixing use and is around 8.5m x 3.5m

Let's take a step back here, and start from basics. Clearly, you came here because you have some serious doubts about the information you were given by a guy who wants to unload tons of his products on you, while he happily pockets your money. And rightfully so! Your doubts are well-founded.

So you came to the right place: We'll give you solid acoustic advice on how to go about this, for free, and we won't try to sell you any products at all. John specifically forbids people from advertising any acoustic products on the forum, even if he uses that product himself! There are several manufacturers who do post on the forum, but they only do so to provide help to forum members, not to openly advertise their products. So nobody here is "out to get you". That's the way it should be: With any consulting service, you should never buy the products from the same guy who recommended them. It's common sense. If a guy sells a product, then clearly he makes money from doing that, so he has an incentive to recommend his product, rather than another better one that he does not sell.

So we can certainly help you out there, by recommending the products but not selling them to you.

However, we'd first need to know a lot more about what you are trying to do! There's a thousand ways that an 8.5 x 3.5m room could end up as a "studio", but only a few of them are any good. In order to guide you to one of those few ways, we'd first need to know all about the room as it is right now, and the other rooms around it on all sides, and what it is that you hope to accomplish when you are done, and how much you plan to spend on doing it, and how much isolation you need, and a whole bunch of other things.

So please post some photos, diagrams, and descriptions of what you have, where you are right now, and where you want to go, and we'd be happy to put you in the best path to get there.

- Stuart -

[CliffParker3]

That would be like someone telling you that in order to get as wet as possible, you need to go sit on the bottom of the ocean, but you should also take a running hose pipe with you to get you even wetter...

Although I've read some great analogies by Stuart that help us laymen wrap our heads around building our spaces -- this has got to be the best I've seen yet. Perhaps some brave soul will drag a running hose to the bottom of the ocean just so we can really know what the effect would be . Thanks Stuart

[Soundman2020]

Thanks, Cliff! Comments like that make all the effort worthwhile. It's good to know that my attempts at explaining in off-beat ways, are appreciated!

- Stuart -

[gio321]

Hahaha. Damn! That was one of the funniest yet most informative posts I've read! Thanks Stuart!

Ok let me explain better what we are trying to do.

We have this space in the first floor of this building which as I said is 8.5m x 3.6m (at it's widest point). This is a temporary space as in around 2 years' time the whole building will be renovated internally by a construction / architectural company and we will be able to re-arrange the whole first floor to our needs. Hence the solution we are looking for now is the best possible, but still won't break the bank as it will only be there for a couple of years.

On the first floor right adjacent to us, there is a dance school / studio. The internal walls are pretty crap, just a few layers of plasterboard. One of the long dimension walls (8.5m) is an external wall (normal brick) and there are rail tracks and trains passing by.

The space will be used both for music production / recording / mixing as well as band rehearsals.
We are trying to minimise the noise from outside which will affect the recording / music production / mixing part, as well as minimise the noise from the rehearsals as there are artists on the floor above us and the dance school adjacent to us. There is none we will be bothering on the floor below us.

The reasoning for the resilient bars is this. Although the stud wall and ceiling will be independent to the existing walls and ceilings, it will be coupled to the floor as we are not treating that for now (cost), which will have impact / vibrations from the dancers next door and the train from the other rooms' external untreated walls.

Green Glue is very expensive in the UK, so the salesman proposed a UK alternative that "does the same job". From what Stuart said it will be a total waste of money to use both GG and Tecsound so I'm thinking we might go with the Tecsound membrane to sandwich between the 2 layers of plasterboard which does a very similar job and adds a bit of mass and there are at least independent lab test results to back this up, instead of going with the untested UK alternative of Green Glue or Green Glue itself (due to cost).

Also keep in mind that the "control room" portion of the room will have a width of only 3m (before treatment) so unfortunately we can't go with building double stud walls or adding many layers of plasterboard as this will reduce the width to unusable dimensions.

On the picture below.
The black lines are the existing walls, the red line is the new stud wall.
The top wall is the external wall, the dance studio is adjacent to the left wall, there is a corridor on the bottom wall, there is a writing studio adjacent to the right wall.
The mixing position will be on the right part of the room facing the right wall. We need to keep the 2 external windows which will be quadruple glass (2 externally on the existing windows and double glass on the stud wall, depicted by the dotted red lines). The thin dotted pencil lines, are a quick drawing of the mixing position (desk on the right) and some other furniture like a couch etc.

Again many thanks for all the input!

[Soundman2020]

Hahaha. Damn! That was one of the funniest yet most informative posts I've read! Thanks Stuart!

Glad you appreciate it, George! A little touch of humor and sarcasm can certainly help a dull day...

Anyway, back to the problem...

We have this space in the first floor of this building ...

"First floor" as in British "first floor", I presume? Meaning one level above the ground, with the "ground" floor below it? Not "first floor" as measure in the USA, meaning the floor that is ON the ground, or AT ground level? (confusing....)

From what you say, I'm assuming British: ten feet above ground level, with another floor below...

On the first floor right adjacent to us, there is a dance school / studio.

Oops! Not good news. That implies loud music, and impact noise.

... and there are rail tracks and trains passing by.

Triple-quadruple ouch!!! That implies structural vibration, oodles of low frequency energy, and probably loud horns too.

You certainly have picked the ... ummm.... "most ideal" spot for a studio! I can't think of much more to add to make it any worse, except maybe if you are one mile off the main runway at Heathrow, directly under the flight path, there's a night club above you, and the local police shooting range for high power weapons and hand grenades is in the room below!!!

Seriously, you have a LOT going against you. I hate being a wet blanket (wet with both ocean water and hose-pipe water, of course), but this does not bode well...

I would suggest that before you make any decisions about how to isolate, you should first get valid data about how bad the problem is. Get a good quality sound level meter, and measure the levels inside your room at the same time a typical dance session is running full-bore next door, and also when some typical trains are rumbling past. In both cases, also borrow a stethoscope and use it to listen to the floor, walls and ceiling when said events are in progress, to see how much of that is in the building structure itslef.

For the sound level meter readings, use the "C" scale and "slow" response, but if the meter also has the option for truly "flat" response then also measure with that (in addition to "C").

Let us know just how bad it is, then we can give you a better idea of how to deal with that.

Hence the solution we are looking for now is the best possible, but one that will not break the bank as it will only be for a couple of years.

OK, so you have the worst-case venue-from-hell, and you want to make it into Abbey Road on a shoe-string budget. OK, got it!

the space will be used both for music production / recording / mixing as well as band rehearsals.

When you say "recording", what type of instruments and genres? It's one thing entirely to want to record a band that thinks Led Zeppelin and Grateful Dead always played way too quiet, and another to want to record "The Whispering Sisters" accompanied by a solo piccolo and two triangles!

We are trying to minimise the noise from outside

With freight trains running right past... I think I'll modify my scenario from the previous post, and suggest that what you are trying to do is akin to trying to NOT get wet from the "bottom-of-the-ocean-plus-running-hose-pipe" by taking an umbrella with you on that outing...

In other words, that's a serious amount of energy you need to block: Trains are heavy, and even on a good track they make buildings shake and vibrate, and put out a lot of low-frequency noise from the locomotive itself (diesel-electric, I presume?). If that sound and vibration is in the building structure, then your chances of eliminating it on a low budget with simple isolation, are way down there between "nil" and "nothing at all".

The reasoning for the resilient bars is this. Although the stud wall and ceiling will be independent to the existing walls and ceilings, it will be coupled to the floor

You didn't mention what the floor is made of, but I'm assuming reinforced concrete? Correct?

Here's the thing with RC (="resilient channel"): it does not make isolation better! That sounds strange, but a lot of things about acoustics are not intuitive, until you understand that underlying principles. What you propose sounds good, intuitively, but in practice won't achieve anything. RC can improve isolation where there isn't any, but it cannot improve isolation where there is. Isolation systems are tuned systems. You probably already know that. The mass of each leaf and the air gap between them are chosen in order to get the MSM resonant frequency as low as possible, because isolation only occurs above that frequency. The "mass" on either side of the wall plus the "spring" in the middle (air) make up the resonant system. More mass = lower frequency. More air gap = lower frequency.

Here's where it gets interesting: You'd think that if one spring in the wall is good, then surely two must be better! If you have the "air" spring and also the "RC" spring, then you'd think that would make an even better "bigger" spring... but it doesn't! The problem is that they work in series (one after the other), not parallel (both at once). In effect, you add the resilience of the air to the resilience of the steel ... and since the steel has much higher resilience, it wins! The air loses. The resulting MSM resonance is now limited by the steel spring of the RC, so it does not matter how big you make the air gap beyond 6 inches, the overall isolation is governed by the RC alone. In effect, by using RC on a coupled wall, you can get an improvement of about 16 dB over having no RC, which is a huge jump, and very worthwhile, but adding RC to a wall that is already decoupled does NOT improve things at all, since the limit is already reached.

To get the full technical details, you should download the paper "NRCC-44692", titled "A Simple model of the sound insulation of gypsum board on resilient supports" from the Canadian National Research council. The introduction to the paper says: "While the model is useful to optimise the low frequency performance of double
leaf constructions with resilient channels, it also demonstrates that the practical range of improvements is limited". In the conclusion section, it says: "The system with the resilient channels has a fundamental resonance frequency that is determined by the combined stiffness of the resilient channels and the air space... The maximum increase in transmission loss due to the addition of resilient channels is about 15 dB and only occurs for cavity depths greater than about 75 mm where the cavities are filled with sound absorbing material."

There's a graph on page 7 of the report (which is actually numbered 221 at the bottom, since it is part of a larger report). Here it is:

maximum-improvement-from-RC-resileint-channel.jpg

As you can see, RC places a LIMIT on how much isolation you can get: it does not IMPROVE isolation at all. Anything beyond 6" (16 cm) is wasted.

In other words, if your air gap is 6" or more, than adding RC is pointless.

Ocean bottom. Hose pipe...

"But!" you say, "I'm not talking about airborne sound!!! I'm talking about structure-borne sound!!! The RC will stop the sound in the studs from getting to the drywall!!" Yep, I hear you. And you'd be wrong there too! Actually, you'd be right, but still wrong...

You'd be right because it would, indeed, help to stop the sound that is in the floor from traveling up those studs and making the drywall vibrate... Very true. But that isn't the problem! The problem is two-fold: Firstly, that very same noise is ALSO in the existing outer-leaf wall, and it will be transmitted across the air gap to the new drywall anyway, to a certain extent, regardless of the RC. And secondly (this is the biggie): the sound is in the floor anyway!!! And you told me that you don't plan to do anything about the floor. So even though you might slightly reduce some small amount of transmission through the walls, by the equivalent of a whisper, you'd still have thirty-one square meters of floor screaming at you! You'd be taking great care to keep the tiny little Capuchin monkey out of the room, while totally ignoring the 800 pound gorilla!

So now we get to the REAL point: Unless you do something to the floor, you'd be wasting money on anything more than mid-range isolation. Isolation is only ever as good as the weakest link, and in your case the weakest like is the floor. Isolating the walls, ceiling, windows, doors HVAC system and electrical system to any level higher than the non-isolated floor, is a waste of time, money and effort.

That's not what you want to hear, I'm sure, (and certianly isn't what the guy in the store told you!) but it's the ugly naked truth.

it will be coupled to the floor as we are not treating that for now (cost), which will have impact / vibrations from the dancers next door and the train from the other rooms' external untreated walls.

Correct, but incorrect. The impact noise coming through your walls is not an issue. The impact noise (including train rumble/vibration) is in the building structure, and there is NOTHING that you can do to get it out again. The untreated walls are irrelevant here: they are not the problem: The problem is the building itself. Impact noise (people dancing, trains rumbling by, as well as people walking, doors opening and closing, toilets flushing, water in pipes, elevators/lifts, pumps, HVAC equipment, etc.) is structure-borne. It is vibration that is running through the actual construction materials of the building itself. And in your case, that translates to the floor.

Here's the kicker, you are on an upper level, with a room below you, so there is no damping on your floor. In effect, your floor is a drum head: a membrane stretched taught across a frame. In this case, the "frame" transmits the structure-borne vibration energy into the floor, when then vibrates happily, and acts as a huge loudspeaker, right under your feet.

That's the real issue: your studio is on top of a drum head.

Green Glue is very expensive in the UK, so the salesman proposed a UK alternative that "does the same job".

If you'll pardon the insulting analogy, that would be like me going to buy a car in China, and being told by the Great Wall salesman: "Rolls Royce cars are very expensive here, but we have something that does the same job"...

'nuff said!

If it ain't Green Glue, then it ain't Green Glue!

so I'm thinking we might go with the Tecsound membrane

Before doing that, I'd ask them for their certified lab test reports, showing how their product actually performs, and compare that to how GG performs. Did you notice that there's no actual acoustic data in their advertising? Just vague claims that it does wonderful things? Red flags... Don't get me wrong! Maybe it works really well! But without seeing the actual data from tests that were done in reputable independent acoustic labs, you can't be sure. Green Glue publishes abundant data about how their product works, with dozens of tests done at very reputable places like Riverbank labs. I looked for similar data on the Tecsound website, but couldn't find much. So ask them for it, and if you do get it, then let's compare. If they can't or won't send it to you, then forget it. Go without, and add another layer of drywall. Green Glue themselves recommends that. They openly state that their product is roughly equivalent to adding an extra layer of drywall, but has the advantage of lower cost, less space, and much less weight.

If prices in the UK would make GG more expensive than a layer of drywall, then just add the layer of drywall! If it works out less expensive, then bite the bullet and do GG. No-brainer.

The same applies to that Tecsound product: assuming you do get favorable acoustic data, compare the cost: If it works out cheaper to use their product than it does to ad one more layer of drywall, then by all means buy dozens of square meters of that stuff, but if it is more expensive per square meter, then forget it, and buy drywall.

The math is simple, and once more we get back to the fact the sound waves have very poor eyesight, and just cannot read price tags...

keep in mind that the "control room" portion of the room will have a width of only 3m (before treatment)

Ouch... that's not very big... How long will it be?

unfortunately we can't go with building double stud walls

Then I must be very confused about what I'm seeing, and what you said before, because your diagram does seem to show a black "existing" wall and a red "new" wall, and you did talk about "independent" walls yesterday... that looks an awful lot like a 2-leaf wall to me! It seems to me that you are ALREADY doing two-leaf walls... so why do you say that you can't do two-leaf walls, when that's what your diagram shows?

we can't go with building double stud walls or adding many layers of plasterboard as this will reduce the width to unusable dimensions.

Then compensate! There's more than one way of skinning a cat, as the saying goes. If you don't have room for large air gaps and thick leaves, then use smaller air gaps and thinner leaves of higher density!

The equations for calculating MSM resonance only have variables for mass, air-gap, and damping. If the air gap must be small, then the mass must be large, If you don't have space to use low-density mass, then use high-density mass. Instead of drywall, use something that has even greater density. There are several materials... Your cost will go up, of course, but you can't eat your cake and have it too. You can't have lots of space AND high isolation AND low cost. You can have space. Or mass. Or cheap. Or isolation. Choose any two, but only two, and the other two automatically go the other way...

The black lines are the existing walls, the red line is the new stud wall.

Bingo! So that's even more confusing, since two minutes ago you said: "we can't go with building double stud walls", yet here you are showing exactly that!

So what is the situation then? Are you doing "existing black walls plus new red walls", or are you not? If you are, then you have a two-leaf system, which is all you need. If not, then I don't get the black-and-red thing.

We need to keep the 2 external windows which will be quadruple glass (2 externally on the existing windows and double glass on the stud wall,

A SIX LEAF system??? Seriously? Have you looked into the implications of multiple-leaf resonant systems? Are you aware that each time you add a leaf of mass over a thin air gap, the resonant frequency of the entire system goes UP, and the low frequency isolation goes DOWN? Your biggest problem here is very low frequency isolation (trains, for example...) A six-leaf window would be absolutely amazing at isolating the piccolos and triangles, and all other high-frequency sounds. Incredibly good. Very high isolation, without any doubt. But at the opposite end of the scale, down where kick drums, bass guitars, and locomotives live, you'd be trashing it.

What is on that existing external window right now? I'm guessing that it is a typical commercial-office-building type double-glazed unit? And I'm also guessing that you cannot replace it with something else, due to building by-laws, etc.? If so, that's fine. If that's the case, then the solution isn't that hard: in your new inner-leaf wall, you will put one single pane of thick laminate glass, and that's it. The thickness can be calculated once all the other parameters are known.

Yes, that would be a 3-leaf system, which is of course worse than a two-leaf system, but it is still way better than a six leaf system, and it is possible to compensate for the 3-leaf effect.

Again many thanks for all the input!

You're welcome!

And here's some more...

Your biggest problem is still the 800 pound gorilla: your floor. That's where all of the impact noise is going to manifest itself. It does not matter what you do to the walls, ceiling, windows, door and HVAC system, once you get beyond the isolation level of what the floor can provide, all the rest is wasted money. So for example, if you figure out that your floor can provide 35 dB of isolation, then doing the walls to 50 dB makes no sense at all.

Of course, for impact noise, you should be looking at IIC ratings, not so much transmission loss. Take a look at the document IRC RR-169 (also from Canadian NRC), to get an idea of the problem you are facing. IR-766 might also be of interest. Without doing anything to the floor, I doubt that you'd be getting IIC better than about 28 or so, if that. A typical 150mm concrete slab all by itself will get you barely IIC 25. Assuming yours is a bit better: IIC 28, maaaaaybbe 30, on a good day. That's not very heartening, considering that you should be shooting for the 50-something range...

So what's the solution?

This is the sad part: There isn't any low-cost, simple, effective solution. I wish I had better news, but that's what they laws of physics say, and without resorting to magical incantations, there's no way around those (in fact, even with magical incantations, there's still no way around them!)

The solution that ISN'T low cost and simple, is to float your floor. You might think that means: "Cool" Rubber pucks and plywood! No problem!" Except that you should take a look at IRC-IR-802 first. You'd soon learn that such light-weight solutions are fantasies. Not only do they NOT improve isolation, they actually make it WORSE. For low frequencies, you can expect a REDUCTION in isolation of several decibels, in the region below 200 Hz (ie, in the region inhabited by kick drums, bass guitars, organs, pianos, electric guitars, dancing neighbors, and passing trains.)

Your real solution is floating your floor properly, which implies a concrete slab floated on proper idolaters. But that costs money, and likely it is more money than you are prepared to spend at this point. You'll have to do that anyway, when the full remodel comes, so you might want to think about it now at least.

Bottom line: RC and polymer mats are not going to do what you want, and are certainly not going to do what the salesman is trying to convince you they will do. But don't take my word for it: download the documents that I mentioned (they are available for free), and check for yourself. If you feel like a laugh to brighten you your sad day, show those graphs to the salesman and ask him once again how his proposed solution will beat the laws of physics and accomplish what the graphs say is impossible... Also ask him what equation he used to calculate the resonant frequency of the system he is proposing, and how many decibels of isolation it will provide... Ask for that in writing, signed and guaranteed... (You could even video-tape his reaction, and put it on YouTube... actually, maybe that's not such a good idea!)

So, getting back to reality: the real issue here is not your walls, but your floor. If you didn't have a dance studio next to you and a railroad outside your window, you'd stand a much better chance, but dealing with those gorillas takes us back to the "venue from hell" issue: you pretty much picked the worst possible spot to have a studio that needs to be silent!

Solutions: There are some things that you can do to mitigate the issues, to some extent (a "drum riser" style floor would help, for example), but the real solution is not what you are being sold by the fast-talking salesman.

The real solution in your case is a floating floor.

That's a phrase that you won't hear me say very often. 99 times out of a hundred, you'll see me trying to dissuade people from floating their floors, but you are that one "other" case: number 100. Not among the 99. Your case is very different, so I had to force myself to type those words very carefully, without putting a "do not" in the middle.

Below is a link to an interesting thread that I often direct people to, when they insist on floating their floors unnecessarily, but I'm directing you to it for the opposite reason: because you DO need to do it. It gives you an idea of what is involved:

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

OK, now maybe I'm terribly wrong in my guesstimates, and the dance studio is only for 3 year old kids who wear soft padded fluffy sheepskin slippers and only ever shuffle softly to quiet lullabies, while the train track is just from a kid's model electric train set, two miles away ... in which case you can ignore all of what I said! (or most of it at least). But if we really are talking full-size building-shaking trains thundering past within a few dozen meters of your studio, and full-sized adults thumping and thudding on the same floor as you, right next door, then please don't ignore it. (And if those adults are learning to tap-dance with clogs on, using Led Zepplin soundtracks, then your problem is even worse than I imagined!)

The end of the story is this: there ARE solutions to get you from where you are to where you want to go. They are not cheap, and you won't be able to buy them at the store that wants to sell you RC and GG and SY50 and "soundplank" (whatever that is!) and all the rest of it. There are some things you can do get reduce sound levels to a certain extent, but your specific case is a real tough one, and getting good levels of isolation is a lot more complex than your friendly salesman with the dollar signs in his eyes, would have you believe.

Sorry I don't have better news for you, but that's reality.


- Stuart -

[gio321]

Thanks again for such a detailed reply Stuart.

You are right about the walls being 2 leaf with the new construction, I just meant that the existing wall is not a "proper" acoustically treated stud wall (with mineral wool etc). My mistake, I'm very new to all these terms!

Good news is that I might have found the Green Glue cheaper than the Tecsound panels, so we'll go for Green Glue instead of those panels.
Just to answer your question about the "sound plank", It's just 19mm thick plasterboard, cheap as normal plasterboard, they call this one plank for some reason..It's 15Kg/m2 and the 12.5mm plasterboard is 10Kg/m2

Concerning the resilient channel, from the graph you posted, I understand that with less than 6'' gap between the existing wall and the new stud wall, we will have gains using RC. We can't afford to have a 6'' air gap due to size constraints (as I told you 3m before treatment is the width of the control room portion). We are planning for a 1''-1.5'' max air gap between the stud walls. This will bring the width at around 2.7m which is barely usable for now. Unless I didn't understand again how the air gap is measured...I assume from the existing wall to the beginning of the new stud wall.

Thanks for the windows tip as well. They are basically single glass. So from what you said, we'll just insulate/seal the existing windows the best we can and then add a double glazed window to the new wall in order to get the triple leaf. The existing windows will be around 3 feet away from the new windows so correct me if I'm wrong, the triple leaf effect will be sort of compensated for?

At this stage building a new floor is not worth it and impossible, just getting the planning permissions, structural evaluation etc. We will sort this one out in a couple of years when the building will be torn apart anyway.

Is there an intermediate easy solution for now that will improve things a bit? You mentioned a "drummer riser" like floor for example.
The trains are not too bad, in the sense they are passenger trains without heavy load and the tracks are pretty decent in the area so there are not extreme vibrations. Also the dance school is mostly young kids. Still not ideal, but I can live with a little bit of impact noise for now especially from the dance school as it is only 2-3 hours a day.

Would a solution for the floor of 100mm 60kg/m3 rockwool (or 50mm 100kg/m3 for more stiffness) -> 19mm plank -> 12.5mm plasterboard -> 12.5mm plasterboard -> 19mm plank -> laminate flooring be good enough for now? Again not to eradicate the vibration problem, just to make things a bit better.

Also since we are on the 1st floor (UK terms), not on the ground floor, we are on the floor above, would all this extra building material we are putting, which I calculate will be around 6,000 Kg total, cause any issues?
I assume it will not as the architects who made the plans and the builders who all visited the place didn't mention anything, just asking if anyone has experience on this.

[Soundman2020]

Unless I didn't understand again how the air gap is measured...I assume from the existing wall to the beginning of the new stud wall.

It's the depth of the cavity, from surface to surface. Imagine that you could somehow shrink down to stand inside the wall cavity, and take a tape measure with you. Measure the distance from the surface that you see on one side of you, to the surface that you see on the other side of you, ignoring the insulation. Just hard, solid surface to hard, solid surface. That's the "air gap", regardless of whether or not it is filled with insulation. That's what you use for calculating the resonant frequency, and hence the transmission loss.

Is there an intermediate easy solution for now that will improve things a bit? You mentioned a "drummer riser" like floor for example.

That's possible in theory, but might not be allowed by your building code for the entire floor. to do that, spread 2" of OC-703 across the entire existing floor, wall to wall, and place two layers of 3/4" plywood (or OSB) on top, screwed together. Cut the plywood so that it does not touch the walls at any point: leave a gap of a few mm, and seal that with acoustic caulk or other good quality very flexible caulk that does not ever harden. It's not a true floating floor, but it can help to knock a few dB off, and it will definitely reduce impact noise getting into the building structure. But do check your local code first, to find out if that is allowable. Lay laminate flooring on top of that, with suitable underlay, once again taking care that the flooring does not touch the walls at any point. If you use skirting board, raise it up a few mm on the side walls so that it does not touch the flooring.

would all this extra building material we are putting, which I calculate will be around 6,000 Kg total, cause any issues?

I can't tell you that. You0d have to hire a qualified structural engineer to take a look and crunch some numbers, to see if that's OK or not.

I assume it will not as the architects who made the plans and the builders who all visited the place didn't mention anything, just asking if anyone has experience on this.

The only person who is qualified to tell you that, both legally and just from the point of view of common sense, is a certified structural engineer. He will go to your building, look, measure, calculate, and then answer the question. When it comes to critical safety issues that could kill you, don't rely on "I assume" or "I think", or "I hope".... or even opinions over the internet.... DANGER! Pay the extra money and get the real export out there to do what he does, and then put it in writing for you. It's not worth risk your life (and the lives of many others) to save those few dollars / pounds / euros / yen / rubles / pesos / whatevers.


- Stuart -