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PostPosted: Fri Jan 22, 2016 5:20 am 
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Joined: Sat Oct 04, 2014 3:02 am
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Location: Berlin, Germany
Hi guys,

first of all this is my first post, although I have been coming time and time again to the forum for information. It's always a nice read and the members are very nice. This is why I come here today to ask something that puzzled me.

Me and my partner accepted a few months ago a project which consisted in planning and assisting in the construction of 6 studio rooms in a 160m2 hall with 4m ceilings. The guys that were going to be using the studios took on the construction. We planned the rooms with wooden frames sitting on Sylomer, with the ceiling (3,80m in 4 rooms and 3,50m in the other 2 rooms) sitting on two of the walls. I calculated the total weight of each wall (including ceiling on those which applied) and chose the correct Sylomer type and length for each wall. Hard work considering the rooms are not only rectangles but pentagons or even more complex. The flooring would be a dry screed with a gravel base, Floorrock 40mm (Rockwool) and on top 25mm Fermacell screed and 12,5mm Fermacell Fiberboard. All the walls, ceiling and flooring have Green Glue between the layers. 100mm Sonorock was fitted behind each wall and the distance between walls is 250mm (for around 21Hz Resonance between the walls).

The guys have finished the construction and now the last details are being done, however I have realized something that I wouldn't have expected out of my theoretical knowledge. When I stomp hard with my fist in one wall in one of the rooms, the vibration can be felt and heard in the next room although these two walls are supposed to be mechanically decoupled through actually 2 layers of Sylomer (one under each wall).

How do you think the vibration is getting through, from one wall to the other? Is the air the conductor? Since the walls are limp (the nature of plasterboard), could it be just the air between the layers short-circuiting the two walls? What do you think?

If you think I'm missing info, please let me know.


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PostPosted: Fri Jan 22, 2016 10:55 am 
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Joined: Thu Aug 21, 2008 10:17 am
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Location: Santiago, Chile
Hi there "Hache", and Welcome!! :)

Quote:
We planned the rooms with wooden frames sitting on Sylomer,
Why? Is there something wrong with the original floor? Is that floor concrete?

Also, how did you attach the wall framing to the sub-floor, through the Sylomer, without coupling it again?

What loading do you have on the Sylomer (kg/m2), and how much is it deflecting under that load?

Quote:
with the ceiling (3,80m in 4 rooms and 3,50m in the other 2 rooms) sitting on two of the walls.
Why is the ceiling sitting on only two walls of the room? It should be sitting on all 4! What are the other two sides of that ceiling attached to?

Quote:
I calculated the total weight of each wall (including ceiling on those which applied) and chose the correct Sylomer type and length for each wall.
Are you certain that the loading is even and linear? It is possible that some parts of your framing are heavier or lighter than others. Did you account for that?

Quote:
The flooring would be a dry screed with a gravel base, Floorrock 40mm (Rockwool) and on top 25mm Fermacell screed and 12,5mm Fermacell Fiberboard.
Once again, why? What is wrong with the original floor that makes it unusable as it is? If it is concrete, then is it badly cracked, or uneven, or flaky?

I'm trying to understand why you are not using the original floor.

Quote:
All the walls, ceiling and flooring have Green Glue between the layers. 100mm Sonorock was fitted behind each wall and the distance between walls is 250mm
How are those walls built? Please describe, in detail, layer by layer, what I would encounter if I were to cut through one of those walls. Something like "16mm drywall, Green Glue, 18mm MDF, 40x90 stud with 90 mm mineral wool, 50mm empty air, 40x90 stud (with 90 mm mineral wool), 16mm drywall, Green Glue, 16mm drywall" or whatever it happens to be in your case.

Quote:
(for around 21Hz Resonance between the walls).
Which equation did you use to arrive at that conclusion?

Quote:
The guys have finished the construction and now the last details are being done,
Are all of the doors and windows in place, with their respective seals?

Quote:
When I stomp hard with my fist in one wall in one of the rooms, the vibration can be felt and heard in the next room although these two walls are supposed to be mechanically decoupled through actually 2 layers of Sylomer (one under each wall).
The Sylomer (if it is doing anything at all) is only reducing vibration transmission into the original floor. It is NOT reducing airborne coupling between the two leaves of the wall. That is an entirely different mechanism.

Quote:
How do you think the vibration is getting through, from one wall to the other? Is the air the conductor?
Yes, definitely. Air is a very good conductor of sound and pressure waves over short distances.

Quote:
Since the walls are limp (the nature of plasterboard),
They are not limp: they are rigid, but slightly flexible. MLV is limp mass. Most rubber sheeting is limp mass. Fabric is limp mass. Plastic is limp mass. Even lead sheeting is somewhat limp (or at least, self-damping). But drywall is not limp. It is rigid.

Quote:
could it be just the air between the layers short-circuiting the two walls?
It is not short-circuiting the leaves: it is doing what it is supposed to do. It is acting as a spring within the MSM system that the wall creates. MSM systems have a resonant frequency, and any sound at that frequency will not only get through clearly, but might also be amplified. Any sound up to 1.414 times the resonant frequency will be transmitted. Above that, mass and damping are the governing factors, and below that rigidity is the governing factor. Drywall is rigid, but partly flexible, so it does not do a very good job of reducing transmission for frequencies below MSM resonance.

I would suspect that the impact noise from your hand hitting the wall is either in the MSM resonant range or below, or that it is purely the impact that is creating an over-pressure condition that is transmitted across the wall.

I would not use a "thump-on-the-wall" test to see how well a wall is isolating. Rather, I would play loud full-spectrum music on full-range speakers in one room, at a known level, then measure the level received in the adjacent room. If the difference between those two levels is not at least as great as the design TL for the wall, then there is another problem somewhere. If it is as high as, or higher than, the designed TL, then there is nothing to worry about.

The walls are supposed to stop loud music getting through, not impact noise.

Please answer all the above questions as well as you can, and also provide a sketch of the facility, as well as a couple of photos of the rooms in question. If you have photos of how the rooms were built, please post some of those as well eg, while the framing was going up, when the HVAC silencers went in, when the windows were installed, when the drywall went on, when the doors were installed, when the door seals were installed, etc.

- Stuart -

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I want this studio to amaze people. "That'll do" doesn't amaze people.


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PostPosted: Fri Jan 22, 2016 7:41 pm 
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Joined: Sat Oct 04, 2014 3:02 am
Posts: 2
Location: Berlin, Germany
Soundman2020 wrote:
Hi there "Hache", and Welcome!! :)


Quote:
Quote:
We planned the rooms with wooden frames sitting on Sylomer,
Why? Is there something wrong with the original floor? Is that floor concrete?

Also, how did you attach the wall framing to the sub-floor, through the Sylomer, without coupling it again?

What loading do you have on the Sylomer (kg/m2), and how much is it deflecting under that load?


Yes the wall framing is sitting on the Sylomer. I calculated the Sylomer using Getzner's own "FreqCalc" program to obtain the resonant frequencies of each wall section.

For each wall section, the deflection is different, since the pressure (Kg/mm2) is different, and each Sylomer Type has different load deflection curves.

I accounted for the long term deflection also and required the builders to keep a clearance between the plasterboard and the subfloor of at leas 8mm at the end of the construction (when the load is maximum) to account for the long term deflection. All gaps were of course sealed using Green Glue sealant.


Quote:
Quote:
with the ceiling (3,80m in 4 rooms and 3,50m in the other 2 rooms) sitting on two of the walls.
Why is the ceiling sitting on only two walls of the room? It should be sitting on all 4! What are the other two sides of that ceiling attached to?


Why? The framing is made using construction wood (KVH) beams. We calculated the weight of the ceiling and the bending of the wood beams under that load and adjusted the amount of beams per m (in the width dimension). Since these beams carry the weight to two or three walls, those walls carry their respective % of the weight which is dependant on the % of surface of the ceiling that sitting and this is adjusted for in the Sylomer calculation. I don't see the problem at all in sitting the ceiling on two or three walls and it's much easier than sitting on all walls. In some cases as you will see in the attached plan, the weight sits on more than 2 walls.

Quote:
Quote:
I calculated the total weight of each wall (including ceiling on those which applied) and chose the correct Sylomer type and length for each wall.
Are you certain that the loading is even and linear? It is possible that some parts of your framing are heavier or lighter than others. Did you account for that?


No, but I adjusted for the "unevenness" and created subsections. Of course there were differences. You will see in the plan.


Quote:
Quote:
The flooring would be a dry screed with a gravel base, Floorrock 40mm (Rockwool) and on top 25mm Fermacell screed and 12,5mm Fermacell Fiberboard.
Once again, why? What is wrong with the original floor that makes it unusable as it is? If it is concrete, then is it badly cracked, or uneven, or flaky?
I'm trying to understand why you are not using the original floor.


Simple, because the original floor would create a flank if you don't decouple the studio floor from the concrete floor underneath. In the best case, we should have built a concrete plate for each room sitting on Sylomer or springs, and then built the wooden framing on top. This was impossible since the ultimate (bearing) load of the concrete subfloor was 5KN/m2 which would have not allowed us to build this way. We would have surpassed the bearing load of the floor once we include the live load (2KN/m2) which is obligatory in Germany.

Therefore the decoupling occurs by using low dynamic stiffness Florrock HP with 40mm thickness with enough weight on top, to achieve a low enough resonance (25 Fermacell screed plus the 12,5 Fermacell fiberboard plus Green Glue, although Green Glue here was a bit overkill).


Quote:
Quote:
All the walls, ceiling and flooring have Green Glue between the layers. 100mm Sonorock was fitted behind each wall and the distance between walls is 250mm
How are those walls built? Please describe, in detail, layer by layer, what I would encounter if I were to cut through one of those walls. Something like "16mm drywall, Green Glue, 18mm MDF, 40x90 stud with 90 mm mineral wool, 50mm empty air, 40x90 stud (with 90 mm mineral wool), 16mm drywall, Green Glue, 16mm drywall" or whatever it happens to be in your case.


Sorry for the lack of info. Layers are: 12,5mm Knauf Silentboard - Green Glue - 18mm Knauf Diamant - Green Glue - 12,5mm Knauf Diamant - 100mm Wood Studs with 100mm Sonorock - 50mm air - 100mm Wood Studs with 100mm Sonorock - 12,5 Diamant - GG - 18mm Diamant - GG - 12,5mm Silentboard.


Quote:
Quote:
(for around 21Hz Resonance between the walls).
Which equation did you use to arrive at that conclusion?


f=850/(SQRT(m*d))
where m is the weight of each wall layer and d the distance between them.
Extracted from "Schallschutz in Gebäuden" by Guido Dietze.
I correct, the Resonance was 24Hz and not 21Hz. 21Hz is from another Project. According to your formula fisol=fres*1,414 where fres is the resonance frequency of the wall and fisol is the frequency at which the wall starts isolating, we should isolate from 34Hz onwards, right?


Quote:
Quote:
The guys have finished the construction and now the last details are being done,
Are all of the doors and windows in place, with their respective seals?


Yes, they are, we want to cover the gaps not only with sealant but with a rigid material which will also optically cover the gaps. The doors are Rw=46dB. There are no doors between loud rooms.
The windows are our own design, and don't have an Rw measured in a lab. However they are made of laminated glass. Laminated glass is 4mm float-0,78PVB-5mm ESG-0,78PVB-4mm Float-0,78PVB-5mm ESG. The gap between the glass layers is 138mm at the shortest and 171mm at the furthest (one the glasses is inclined at the requirement of the customer).


Quote:
Quote:
When I stomp hard with my fist in one wall in one of the rooms, the vibration can be felt and heard in the next room although these two walls are supposed to be mechanically decoupled through actually 2 layers of Sylomer (one under each wall).
The Sylomer (if it is doing anything at all)
I don't know why you doubt so much the sylomer is doing anything at all :cop: It is calculated correctly and in all cases resonances are well below 12Hz which means from 20Hz onwards the isolation is greater than 90%. (FreqCalc results)


Quote:
is only reducing vibration transmission into the original floor. It is NOT reducing airborne coupling between the two leaves of the wall. That is an entirely different mechanism.

Quote:
How do you think the vibration is getting through, from one wall to the other? Is the air the conductor?
Yes, definitely. Air is a very good conductor of sound and pressure waves over short distances.

This is the answer I was looking for. This is a perfectly normal mechanism that can't be avoided, besides by placing the walls 40cm apart or more.

Quote:
Quote:
Since the walls are limp (the nature of plasterboard),
They are not limp: they are rigid, but slightly flexible. MLV is limp mass. Most rubber sheeting is limp mass. Fabric is limp mass. Plastic is limp mass. Even lead sheeting is somewhat limp (or at least, self-damping). But drywall is not limp. It is rigid.


I might have used the wrong word. In construction terminology, in Germany, there's a clear distinction between "Biegesteif" or "bending stiff" (i.e. concrete, a massive wall) and "Biegeweich" "bending soft". Plasterboard, specially for example Knauf Silentboard is "Biegeweich". The more "biegeweich" a material is, (and in direct relation to the thickness of the material), the Coincidence Frequency is higher displacing it from the more audible frequencies.

Quote:
Quote:
could it be just the air between the layers short-circuiting the two walls?
It is not short-circuiting the leaves: it is doing what it is supposed to do. It is acting as a spring within the MSM system that the wall creates. MSM systems have a resonant frequency, and any sound at that frequency will not only get through clearly, but might also be amplified. Any sound up to 1.414 times the resonant frequency will be transmitted. Above that, mass and damping are the governing factors, and below that rigidity is the governing factor. Drywall is rigid, but partly flexible, so it does not do a very good job of reducing transmission for frequencies below MSM resonance.

I would suspect that the impact noise from your hand hitting the wall is either in the MSM resonant range or below, or that it is purely the impact that is creating an over-pressure condition that is transmitted across the wall.

I would not use a "thump-on-the-wall" test to see how well a wall is isolating. Rather, I would play loud full-spectrum music on full-range speakers in one room, at a known level, then measure the level received in the adjacent room. If the difference between those two levels is not at least as great as the design TL for the wall, then there is another problem somewhere. If it is as high as, or higher than, the designed TL, then there is nothing to worry about.


Sorry, my English terminology knowledge is not as good. What does TL stand for?

Quote:
The walls are supposed to stop loud music getting through, not impact noise.

Please answer all the above questions as well as you can, and also provide a sketch of the facility, as well as a couple of photos of the rooms in question. If you have photos of how the rooms were built, please post some of those as well eg, while the framing was going up, when the HVAC silencers went in, when the windows were installed, when the drywall went on, when the doors were installed, when the door seals were installed, etc.

- Stuart -
Find the plan in the link at the bottom.

Thanks for your reply Stuart, really, much appreciated. Yesterday, after thinking about the problem, it was clear to me that it had to be the MSM system between the wall-air-wall, that's what I meant by short circuiting. I thought that since the sudden air pressure change would not allow to be dissipated on such a big surface, and it basically acts as a enclosed system with two membranes.

I will be testing today and will post the results. The problem was: there was no electricity in the rooms to be able to test anything with speakers so far. My intention is to measure with pink noise at 0,5m from the source and in the next room. Then also do measurements with sine waves at 31,5Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1KHz, 2KHz 4KHz 8KHz and 16KHz in both rooms and plot a graph for D for each octave and then calculate R'w. Rw of this type of wall is according to Knauf 72dB which will always be less in real life. Therefore, accounting for the windows between the rooms, 70dB difference should be more than acceptable. What do you think?

https://owncloud.rummels-acoustics.com/ ... ozNLMSHXgN


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