double leaf effect cost more than triple in most situations.

[Eric_Desart]

The curves are similar. Above the concrete (block or slab) critical frequency the added leaf provides advantage. Below that critical frequency the concrete (solid or block) alone is superior. As predicted by Mass Law.

Don't confuse critical frequency (referring to coincidence) with Mass-Spring resonance.
Indeed concrete blocks and glass bricks behave as single leaf (hollow or not)

So lastly I ask how does a standard coupled double leaf wood framed ceiling behave when a third leaf is added? Starting on page 70 of the NRC’s IR811 study I find some rough comparisons that might help me.

I see that adding a third leaf to the traditional framed double leaf does not de-rate the system, and does not appear to negatively affect the low frequencies, at least down to the available data limit of 50Hz

So I could infer that the addition of a third leaf to an existing double leaf may not reduce the low frequency transmission loss. I might further infer that due to the stiffness of the hollow block, it does not behave as a double leaf, but rather behaves more like a single leaf.

Clearly these triple leaves are a waste, but that wasn't the point.

You call it a traditional double leaf, I call it a sick double leaf. That original curve is dominant defined by structural resonance, and the added panel by 2 things:
1) far to the left of the resonance around 200 Hz (you have a cavity of only 13 mm) these 2 panels start moving in phase (restoring themselves to the mass law of both panels together, meaning that these panels further below the MSM start acting as a single panel as if that cavity hardly exists = standard behavior) and
2) the resonance itself is strongly damped to the extreme small cavity (visco-thermal acousto-elastic interaction - see Tom Basten ISBN 90-365-1597-1)

Wat I do notice is that on the same pages in this report you refer there are combinations wih more logical cavities where the phenomenon becomes more clearly. These you don't speak about.
As long as the others don't get confused here it's OK for me.
I also agree with xSpace: wat you see on that typical picture are STC values. A higher STC value is a higher STC value, nothing else. For years people are telling that STC isn't representative for low frequency content, or studio use.
For me that picture has no other value than showing the idea of MDOF systems (Mass-Spring systems with Multiple Degrees Of Freedom).
That's a typical picture once taken from a UK site (which is afterwards removed by them) and that went into the traditional copy/past net procedure, where giving sources are more of a sin than a virtue.

Mass-spring principles applying on STC values based on measurements where structural resonance is, or can be, a dominant factor is like comparing apples with oranges.

Ted, why do you think I'm so careful in expressing myself physically, if you try to get me to confirm simplified statements/conclusions?

[Eric_Desart]

Mass-spring principles applying on STC values based on measurements where structural resonance is, or can be, a dominant factor is like comparing apples with oranges.

An Example:
http://www.nrc-cnrc.gc.ca/obj/irc/doc/p ... c44692.pdf
A Simple model of the sound insulation of gypsum board on resilient supports
Bradley, J.S.; Birta, J.A.
NRCC-44692
Look at fig. 2 on the 3rd page (p 217)

NRCC-44692 fig2.png

3 walls are build-up to test possible differences between 3 different RC models. That bad curve is the same wall based on wooden studs without any RC.
What you see are structural resonances and flanking. With such a wall you can try to stylize the problem to a mass-spring resonance (MSM). But it has hardly sense since you're looking, from an acoustical point of view, to a sick wall build-up dominated by whatever other phenomena.
These 3 RC versions you can apply some simplified reasoning, that acoustically bad version you can, as a matter of speech, make and end-work of it.

If Green Glue, Brian tells that doubling the panels on a wooden stud wall only gives a couple of dBs then that is because he compares acoustically 2 bad walls dominated by other phenomena than the doubling of the mass/panels on both sides.

[AVare]

I don't think you can necessasarily equate the reactions of a masonry wall as the starting point with the original question which has to do with a frame wall and drywall on both surfaces.....

Thanks Rod. I was giving an example of where adding a third leaf reduces LF TL. As far as the original question, or statement goes, I can not figure out exactly what the OP meant.

As far as the suitability of a CMU wall for triple leaf effect goes, mass is mass. CMU units act acoustically for the most part as mass, not a double leaf. This is evident from the TL curve for the bare wall.

Here is an example from IR-766 pdf pages 124 and 125. It is a floor system, but the material densities are closer to walls. Examples 1 and 4 use identical material, but in different ways. The design with the third leaf has an STC 17 points lower than the one without. Unfortunately I have not been able to find the TL data for the tests. Of course the usual STC applicability qualifier is emphasized.

As an edit because I posted the above earlier, IR-811 has the TL data on pdf page 72.

Andre

[rod gervais]

"Ted is absolutely correct in what he is saying, and the chart proves it...."

No he isn't and I haven't seen the chart that proves it.

xSpace,

the chart I am referring to is the one posted by Stuart...... take a look at it please......

In the most simple of forms........ if you begin with a single stud double faced wall - and you build a wall adjacent to it - adding another face - (all things being equal)this will increase your isolation - not decrease it. Which is the point Ted is trying to here here.....

The fact that you can add some fairly drastic additional isolation by taking just that 3rd leaf and relocating it to one of the outmost wall surfaces is not relevant to the point he is making.

I always tell people to avoid the 3 leaf whenever they can - but when they can't - then just live with what they have - and overcome the obstacle with mass........

3 leaf walls are not an insurmountable problem, and they cannot ALWAYS be avoided.

When they can't be avoided this doesn't mean that the people who own the property are automatically screwed and will never acheive decent (or even great) isolation - but rather, they are just going to have to work a little harder (and smarted) to acheive their goals..

Sincerely,

Rod

[AVare]

I always tell people to avoid the 3 leaf whenever they can - but when they can't - then just live with what they have - and overcome the obstacle with mass........

3 leaf walls are not an insurmountable problem, and they cannot ALWAYS be avoided.

When they can't be avoided this doesn't mean that the people who own the property are automatically screwed and will never acheive decent (or even great) isolation - but rather, they are just going to have to work a little harder (and smarted) to acheive their goals..

+1. The biggest problem, as I see it, is people taking as absolute what are generalizations, without knowing the factors involved. I think this is about the fourth time I am writing this week that "acoustics is not intuitive and requires detailed knowledge to do properly and cost effectively."

Andre

[Soundman2020]

3 walls are build-up to test possible differences between 3 different RC models. That bad curve is the same wall based on wooden studs without any RC.
What you see are structural resonances and flanking.

Eric, I'm just curious here: On that graph that you posted from NRCC-44692, the resonance dip seems to drop from about 120 Hz. on the basic wall to about 60 Hz. with all three types of RC. Is that drop due to the decoupling provided by the RC, or to the deeper air gap, or to something else?


- Stuart -

[xSpace]

I don't believe inserting a third leaf makes LF worse than before

And that comment from a man that proudly displays a soundproofingcompany.com link in his sig.


Well I admit I have no idea to what the suggestion that Mr. White is correct about because whatever his point was...keeps moving

My opinion has not changed about the initial question, while the initial question has morphed into something entirely different.

I thought it was a general acceptance that a three leaf is just like the existence of spiders, your never more than 3 feet away from one at any given time. So you live with it, try to understand it better, but you still live with it.

I have my own "proof" that a three leaf is not recommended and can support that the LF will in fact be worse as will the TL and the STC and the FSTC and the IIC.

In a nutshell, he may be selling it, but I ain't buying it

[rod gervais]

And if you want the theory behind it, with abundant examples and numerous real laboratory tests, then the best I can recommend is the 1973 Wyle report:

http://www.box.net/shared/jcaoavdc8g

It might be old, but it is still very, very valid. And very interesting reading.


- Stuart -

Stuart,

I never reviewed that document before.......

One thing I found very interesting was that one of their assesments of 3 leaf construction noted that it might be a worthwhile consideration for construction when seeking to take the minimum TL value of the assembly to greater than 20dB...... something they are not seeing as a reasonable consideration with 2 leaf frames.........


Rod

[John Sayers]

This is an interesting thread and I thank all the participants - unfortunately I've just been through a C:/ drive crash and have been busily rebuilding my computer.

Here's a pic to consider - I was amazed that no one picked it up at the time.

lou_1.jpg

taken from

STONEHILL-SD-110108 SHEET2 (A3).pdf

and this

STONEHILL-SD-110108 SHEET1 (A3).pdf

from this thread

http://www.johnlsayers.com/phpBB2/viewt ... =10&t=9156

[Ted White]

John, what was the story behind that partition? That was a very long thread you linked. Maybe you could give a two sentence brief for us.

[Eric_Desart]

Here's a pic to consider - I was amazed that no one picked it up at the time.
<pic removed, to be seen higher up>
taken from

STONEHILL-SD-110108 SHEET2 (A3).pdf

and this

STONEHILL-SD-110108 SHEET1 (A3).pdf

from this thread
http://www.johnlsayers.com/phpBB2/viewt ... =10&t=9156

Lou, You have all reasons to be proud on your work and studio.

But from a building physics point of view, I'm really sorry, that's a stupid design showing that these "The Studio People" don't have related insight and background.
I once had a similar discussion with Galaxy and Eastlake Audio at the Catholic University of Leuven. That's a whole story, but the result was that within an hour Galaxy understood that a big name in the studio world and knowing physics are not the same thing.

Just some additional references I looked up:
http://www.studiopeople.com/clients_st24.asp
http://www.studiopeople.com/index.asp
http://loustonehill.com/studio4_home.html

[Soundman2020]

Here's a pic to consider - I was amazed that no one picked it up at the time.

I'm looking at that pic, and scratching my head, and thinking: "Isn't that a SEVEN LEAF wall"???

Or am I misunderstanding the diagram?


- Stuart -

[Eric_Desart]

Here's a pic to consider - I was amazed that no one picked it up at the time.

I'm looking at that pic, and scratching my head, and thinking: "Isn't that a SEVEN LEAF wall"???

Such a picture makes me angry and stunned. It doesn't matter how many leafs this are. This is drafted by people without related knowledge. Such people sell themselves as related experts.

[Soundman2020]

I'm trying to get my head around this.

Eric, wouldn't a 7-leaf wall have all kinds of internal resonance issues? Wouldn't it also have a pretty high over-all resonant frequency, for the entire "MSMSMSMSMSM" system?

Some leaves are two layers of drywall, some are one, some have large air gaps, some small, some with damping insulation in the air gaps, some not... It must be extremely complex to even calculate the acoustic properties of such a wall, surely?

I just don't get it. It flies in the face of everything that I've learned about acoustics and isolation (which, admittedly, isn't all that much). Apart from being really expensive and hard to build, I just don't see the acoustic logic behind the design.


- Stuart -

[Eric_Desart]

Stuart,

I doubt (99 % sure) that anyone can calculate/simulate that.
One can calculate simple systems at straight incidence, but room acoustics adds a lot of unknowns and uncertainties. (angle of incidence, bending waves in the panels, and so on).
There are animations on the web but I can't find them now.
You have as many resonance frequencies as you have cavities (exacter expressed: degrees of freedom), but this are not the individual resonances per adjacent pair of leafs, but the interactions between all these masses.

At studiotips we have searched at a certain moment to find enough measured data of triple leaf systems, without much success. One can calculate this in a stylized manner which is based on the mechanical response of mdof systems. This works rather perfectly if one wants to calculate silencers. Room acoustics however adds a lot of uncertainties.

If you want to know how a double leaf system works check this animation and play with the parameters and frequency.
http://www.walter-fendt.de/ph14e/resonance.htm

I also find discussing wrong principles in the context of their purpose in a studio forum a bit a loss of time. (I spent some time trying to find clear animations, but without success for now).