Elastic or rigid room in room walls

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Re: Elastic or rigid room in room walls

Postby andrebrito » Wed Jul 29, 2015 1:56 pm

I will compare two cases

Red brick 15 cm - 40 cm rockwool - red brick 15 cm

And Red brick 15 cm - 40 cm rockwool - 2 gypsum boards 13 mm with Green Glue

The last one has better performance than the first one even if the mass per sqm is lower.

There is a huge documentos with tons of information on red brick , concrete and gypsum testa but it is in
portuguese

http://www.preceram.pt/documentos/Prece ... 006_12.pdf
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Re: Elastic or rigid room in room walls

Postby Ido » Fri Jul 31, 2015 1:27 pm

how y'doin Andre?
that document looks amazing and very needed...
could you possibly check if they made an english version?
if not, could you please show at least the 1 important graph that you mentioned (brick versus 2 GG drywall) and say who is who?
thanks
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Re: Elastic or rigid room in room walls

Postby bert stoltenborg » Sat Aug 01, 2015 6:15 pm

The document doesn't show data under 100 Hz, Ido, so for music isolation it is guessing which construction is better.

I think what Eric means is that a stiff construction like a brick wall will perform inferior compared to a wall of the same mass build of sheets of gypsum.
The gypsum sheets can move a bit and that friction improves sound isolation. Also the resonance freq is lower due to that phenomen.

And a gypsum wall with studs every 600 mm is superior to one with studs every 400 mm for it is less stiff and has a lower resonance freq.

It is a bit difficult to compare data when they are taken from different labs, as the size of the device under test, the size of the rooms and the alcohol percentage is of influence.
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Re: Elastic or rigid room in room walls

Postby andrebrito » Sat Aug 01, 2015 7:56 pm

Hi,

That document is only available in Portuguese, all measurements were done on the same lab.

One of the first charts says brick 15 cm + 4 cm + brick 11 with Rw of 52 dB

On the last part of the report they have several charts all dedicaret to gypsum. I think 3 gypsum boards on each side gets around 62 dB.

These reports are from building acoutics mainly so no information below 100 Hz
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Re: Elastic or rigid room in room walls

Postby Ido » Sun Aug 02, 2015 10:27 am

hey Andre,
as you know the issue here is the frequencies and not the STC,
and we are mainly interested in the lower freqs cause we like music :)
Bert, I think even data just to 100 Hz can still give inclination to where things go, no?
as you say, the thing is resonances, and the problem with light blocks is that they have the worst of both worlds, low mass and lower coincidence than drywall sheets (smack in midrange, which is why Eric prolly thought it should be exiled), wheras if I remember right the massive blocks have their coincidence below the 100 Hz mark and anyways their resonance ai'nt terribly sharp/low.
so we would prefer a wall with better LF isolation even if it has lower STC, which I can only guess is what would be with the 2 scenarios mentioned.
really seems like a great paper for us, not to mention comparison of drywall with GG to bricks...
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Re: Elastic or rigid room in room walls

Postby bert stoltenborg » Sun Aug 02, 2015 12:32 pm

I think it is dangerous to just extrapolate/estimate data, Ido.
I'll post some examples later.
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Re: Elastic or rigid room in room walls

Postby andrebrito » Sun Aug 02, 2015 3:41 pm

Hi there,

Bert is correct, that is not accurate to extrapolate data.

Even so, one some of the examples you can clearly see the mass air mass resonance on the charts on the light weight examples.

About the report

Image on page 8 is all about red bricks with different sizes. Ido, not sure if it is possible to translate the document using Google translate, you may try it.

It has tons of information on using different kinds of absorbent materials like mineral wool, but also cork, xps plates etc etc... It is mainly for building construction but still quite useful.
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Re: Elastic or rigid room in room walls

Postby bert stoltenborg » Sun Aug 02, 2015 6:38 pm

These are data from the University of Leuven.
It is a 100 mm limestone wall and the same wall with decoupled double gypsum constructions.
You see that especialy in the low frequencies under 100 Hz you cannot just extrapolate the graphs.
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Re: Elastic or rigid room in room walls

Postby andrebrito » Sun Aug 02, 2015 8:20 pm

Are these results reliable for such low frequencies even below 50 Hz.... Since modal activity is probably high on both the receiving and emitting room... I know for absorption values it can be quite tricky to measure at low frequencies, wonder how does this works for sound transmission loss
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Re: Elastic or rigid room in room walls

Postby Ido » Sun Aug 02, 2015 9:04 pm

hey, what i said on extarpolating data is an insignificant side line,
my point was that it would be good to see a comparison between 2 massive walls and between 1 massive/1 light.
in drywall combos we've seen enough resonance weak spots in the 100 Hz region...
Bert, if i understand correct your graph doesn't show such comparison, no? but Andre's doc does.
also, massive I mean were one is at least 15 cm concrete or 20 cm block, I don't think 10 cm brick is heavy enough.
so for me the right comparison would be a base massive wall of say at least 300 kg surface mass and the second wall would be once a secondary massive wall of at least 200 kg/m2 versus a drywall combo preferably with/without GG,
I would guess the massive combo would be better and steadier in the LF but have lower STC but what do i know...
where's the master when you need him, eh?
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Re: Elastic or rigid room in room walls

Postby andrebrito » Sun Aug 02, 2015 9:32 pm

I got another document in portuguese much simpler to read

http://paginas.fe.up.pt/~earpe/conteudo ... Aereos.pdf

Check pg 8, you will see a comparison with red brick and gypsum....

Red brick, the mass law works, on gypsum it does not.

BTW Brick in Portuguese is "Tijolo"
gypsum is referred as BA13
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Re: Elastic or rigid room in room walls

Postby Ido » Sun Aug 02, 2015 9:49 pm

dammit Bert, we gotta start learnin' portugese...

thanks Andre
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Re: Elastic or rigid room in room walls

Postby andrebrito » Mon Aug 03, 2015 11:10 am

That PDF is from a PowerPoint from a post graduation in acoustics

All the lovely formulas are related to the prediction of sound insulation over frequency or predictions of sound insulation taking into account the flanking transmission.

There are software that can do this INSUL and ACOUBAT but you can also do it with excel l(done it before pain in the ass)
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Re: Elastic or rigid room in room walls

Postby Ido » Mon Aug 03, 2015 11:43 am

seems like good work though even with your guidance I still don't have a clue to what does what :D :bang ...
I have to say in these things I'm interested in the actual measurement data and not the theory (which I understand is the first doc).
so Andre, portugal is back to being a superpower? :mrgreen:
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Re: Elastic or rigid room in room walls

Postby andrebrito » Mon Aug 03, 2015 5:08 pm

All those formulas are quite useful and are to be used with lab measurements.

The main idea is to predict the real sound insulation in buildings with flaking included, which lab measurements don't take into account.

A lab measurement may say 52 dB of Rw but in practice you get 45 dB of R'w for a specific case.

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Re: Elastic or rigid room in room walls

Postby Yannick » Fri Aug 07, 2015 8:58 am

http://old.jhbrandt.net/ir586.pdf

That is imo a very interesting document, which shows well-executed mass cannot be beaten by gypsum board.
I had that discussion years ago with Eric, he did not believe a combination of cellular concrete (150 and 240 mm) with "kalkzandsteen" (150mm) would work in my situation.
I did it that way anyway, based on the STC 79 on page 17.
The 190mm blocks they are using are low-weight concrete, not cellular concrete, but the author believes cellular concrete could be superior (never found the study he was planning to do).
Anyway, the 90mm-90mm graph is still very impressive, and still does not show a coincidence dip (STC 77).

My main point was and is, you are NEVER going to reach 50+ dB isolation around 100 Hz with a 100 mm air gap and several layers of gypsum.

Of course, this only works if the interior room is floated (comparison on p19).
Amazingly, there is a coincidence dip all of a sudden. Could it be this happens only when the 2 wythes are coupled through the floor (the airgap is equal, as is the glass fibre)

Also very interesting is the crap valua of styrofoam in the air gap.

My conclusion would be that elastic walls can be better:
a. if the interior room is not (well-)floated
b. above the resonance freq of the wall

Around and below the wall resonance, a massive wall system should be quite superior (at least 20 dB better than gypsum).
A gypsum wall in front of a brick wall will always behave as a (fairly inefficient) drum skin at LF.
(a very efficient drum skin if it is badly executed)
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Re: Elastic or rigid room in room walls

Postby Ido » Sat Aug 08, 2015 7:36 pm

hi Yannick,

Yannick wrote:...I had that discussion years ago with Eric, he did not believe a combination of cellular concrete (150 and 240 mm) with "kalkzandsteen" (150mm) would work in my situation...)


again, I'm pretty sure it was because of it being cellular, not because of 2 massive walls...

Yannick wrote:...
The 190mm blocks they are using are low-weight concrete, not cellular concrete, but the author believes cellular concrete could be superior (never found the study he was planning to do).
....


do you happen to know the density?
too bad such a serious study and no accurate mention of it.
Bob, if you're reading this, would there be canadian standard bricks fitting the description which you could guess densities?
regarding cellular, I just saw some vague line about it, no more, and I am very skeptic (unless it has good mass)


Yannick wrote:...
A gypsum wall in front of a brick wall will always behave as a (fairly inefficient) drum skin at LF.
(a very efficient drum skin if it is badly executed)


that is too harsh/deterministic/generalizing and in this specific point I will rise up and say "Bert is right" :mrgreen: . damping and carefull design can make em good. not as good as 2 heavy massive in LF, but not necessarily inefficient drumskins.
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Re: Elastic or rigid room in room walls

Postby Yannick » Sat Aug 08, 2015 9:16 pm

The xella/ytong c3 blocks are 485 kg/m3.
This amounts to approx. 120 Kg/m2, plastered, 240 mm thick.
You need multiple layers of gypsum to have the same mass, but I have the impression two other factors are to my advantage (in my situation):

- the wall is thick, and becomes much less resonant than eg. a 100 mm wall with the same total mass
- the wall is load bearing. It is supporting a 46 m2 26 cm thick concrete upper floor slab plus the next floor. This changes the resonant behaviour - cellular concrete or not.

When I play 95 dB plus, bass heavy music in my mastering studio, in the next room I can hear nothing. If it is completely quiet, I can sometimes hear a faint bass line. Whatever comes through is unmeasurable, as it is buried in the noise floor anyway.

It was my argument this stifness should increase isolation at LF. The problem with stiff concrete walls is that they will transmit higher frequencies if they are too light ? It could very well be that cellular aerated concrete is much more lossy at higher frequencies ?
I can try to find the lab measurements I received for the Ytong walls and for the lime-sandstone walls.
Could be interesting to compare with a single wall of concrete or concrete blocks, or eg. 4 layers of gypsum.
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Re: Elastic or rigid room in room walls

Postby Ido » Sun Aug 09, 2015 4:59 pm

Yannick, the real life doesn't always fit into theory patterns we believe in, so when ur talking stiffness etc best listen to Bert..
I think it's not the stiffness working rather it's the pure mass. The downside of these light blocks versus drywall is their resonances in midrange
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Re: Elastic or rigid room in room walls

Postby Yannick » Sun Aug 09, 2015 6:49 pm

I know they are not the most performant in the midrange, but that is why I combined them with Silka blocks, which are outstanding in the midrange.
(1000 1250 1600 2000 2500 3150 4000 Hz
54 56 58 60 62 63 65 dB)


At the same time, these "light" Ytong Blocks actually perform better below 200Hz than a 150mm massive Silka wall, which weighs 2x per m2 !
Hence my thought about the "stiffness" of the thicker wall contributing to something.

Also, the SIlka measurements show a weakness around 160 Hz. I have the faint impression this has more to do with the size (self resonance) of the test sample.
I noticed, I was afraid the 150mm wall was too thin (bumping it made it ring at LF). I tested the same thing on a show, with a 200mm sample, and it was much more inert.
However, when the ceiling beams were suspended on the SIlka walls, the resonance changed.
When 1/3 of the 40m2 ceiling had the second layer of drywall with Greenglue in between, the Silka walls all of a sudden became virtually non-resonant !
This phenomenon happenend between adding 5m2 and 15m2 of second layer already.

To date, I find it a pity I did not record this wall resonance with a contact mic. It was fairly impressive.

IMO other things than sheer mass and thickness can work to our advantage (or disadvantage).
Loading of the wall by a heavy ceiling or not, finishing, the amount of precision in the work, heck even the paint you put onto it :mrgreen:

I worked in a basement room with light gyproc walls on metal studs. LF RT was huge, when I pressed stop during editing, you could actually hear the walls ring for more than a second...

I know I must listen to Bert, but I never extrapolated something out of something.
I just looked at this Canadian study, made a wall in which each wythe outperformed the Canadian STC77 sample, by quite a margin.
I then made sure my inner wall was very well floated (built on a concrete slab, calculated by Getzner themselves).
I made sure all resonances of air gaps and springs were well below the usable LF response in my room.

I remain confident I could never have constructed it this good with gypsum inner walls.
My ceiling is Fermacell (three layers, total thickness 50mm, 2x greenglue, 14 cm Rockwool on top, 25 cm airgap to the 26cm concrete upper floor slab).
When my kids are jumping up stairs, the ceiling is the weak link.

Maybe I made the beam structure too stiff, it could have been more lossy, I don't know. The beam structure behaves basically as one big piece of wood.

On the other hand, airborne noise does not make it down- or upstairs. Ever.
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