double leaf effect cost more than triple in most situations.

[Ted White]

No worries Eric. The stylization is great.

So essentially you're starting Wall #2. Then you add a single leaf insulated 2x4 framed wall to create new wall #4.

You assume a 3" gap between the old leaf and the new frame. Decoupled.

Then you progessively moved that new single leaf wall back in 3" increments.

I believe that's what you are saying. And what did you find?

[Eric_Desart]

I believe that's what you are saying. And what did you find?

That what everyone is saying is correct.

A triple leaf system varies between bad, risky and inefficient unless the cavities become that large (frequency dependent) that the cavity starts acting as a room in itself.

The frequency and wavelength dependency is an complicated business not allowing to put a constant figure on this. And therefore, within normal or traditional space availability, cavity widths, uncertain behavior, it's a good thing that people summarize triple leaf systems as to be avoided whenever possible, and only allowed/accepted when forced by non-acoustic arguments.

Just look at these combinations and the resulting resonance frequencies, where for the triple leaf systems the higher resonance is (within traditional common circumstances) is defining. The idea of designing walls is to get this resonance far below the to be insulated frequency range of interest (at least a factor 2 to 3).

[Ted White]

You're saying that the LF performance of wall system #4 is worse than wall system #2

[Eric_Desart]

You're saying that the LF performance of wall system #4 is worse than wall system #2

That's what you like to hear, but not what I'm saying since also depending on the internal damping of the construction. But correct is that with a complete undamped system this is true.
And that it certainly doesn't improve that wall in a significant manner making it a risky and to be avoided advice to potential customers.

I told that I calculated this in a stylized manner. Nature and structures tend to react a bit more complicated. And I don't gamble, just to make things easier to express.

[AVare]

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

Interesting thread. I have respected your sharing of knowledge, particularly on Avsforum for years. It is difficult to accept things that are contrary to what has been beleived for years, especially if one is an expert in the field.

Hows about adding a third leaf reduces LF TL and STC?

It is all in this thread.

http://johnlsayers.com/phpBB2/viewtopic ... hilit=leaf

Andre

[Soundman2020]

(Stuart can you please enter sources of your pictures?)

Oops! Sorry!

... OK, I just updated the two-graph post with the correct references. I'm not sure where I got that original "several wall" graph from: perhaps SAE? I'll see if I can find the original source. But the link that I posted to Bob Golds page has roughly the same image.

Thanks for keeping me honest!


- Stuart -

[rod gervais]

And thanks once again! We all have heard the ills of triple leaves and the advantage of double. No question on the data. I don't believe inserting a third leaf makes LF worse than before

Ted,

that's because it doesn't........ no question that adding the 3rd leaf - with additional air spring - some more mass and insulation will improve the existing 2 leaf (constructed over a single stud frame)...... it will work every time as long as flanking isn't the weaker link. And that is where the potential problems begin....... you cannot predict exactly how the construction will react without a whole lot of testing...... but (keeping it simple):

The following data is from IR-761

Start with this:TestID TL-93-157 STC 34

1 single layer of 16 mm type X gypsum board
2 90 mm wood studs at 406 mm on centre
3 90 mm of mineral fibre insulation in cavity
4 single layer of 16 mm type X gypsum board

Now look at the next step (I do not have data with the 3 leaf and mineral wool - but the difference is still large:

1 single layer of 16 mm type X gypsum board
2 90 mm wood studs at 406 mm on centre
3 65 mm of glass fibre insulation in cavity
4 25 mm gap filled with CX
5 90 mm wood studs at 406 mm on centre
6 65 mm of glass fibre insulation in cavity
7 single layer of 16 mm type X gypsum board

and you will go from the original to the new - TestID TL-93-297 STC 55......
a gain of 11dB averaged.

BUT - the question is what do you give up...... if you simply slip that middle to one of the outsides you reach,

TestID TL-93-267 - STC 62 - another 11 dB gain just due to placement of materials.

Element Description:
1 single layer of 16 mm type X gypsum board
2 90 mm wood studs at 406 mm on centre
3 90 mm of glass fibre insulation in cavity
4 25 mm gap filled with air
5 90 mm wood studs at 406 mm on centre
6 90 mm of glass fibre insulation in cavity
7 single layer of 16 mm type X gypsum board
8 single layer of 16 mm type X gypsum board

And now - I will address the OP in a seperate response.......

Rod

[rod gervais]

Hows about adding a third leaf reduces LF TL and STC?

It is all in this thread.

http://johnlsayers.com/phpBB2/viewtopic ... hilit=leaf

Andre

Andre,

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.....

But it is a good example of how the science is not intuitive - and that the only real bet is tried, true and tested.......

Rod

[Ted White]

Hi Rod, thanks for weighing in on this topic. Thank you for the data.

Andre, thank you also for that data. I'm also wondering if a block wall is reasonable to compare in this instance. For example the question in my mind becomes “does a block wall behave more as a single leaf or as a traditional double leaf with traditional framing?" I ask because if we look at this progression:

4” poured concrete critical frequency of 225Hz
6” poured concrete critical frequency of 150Hz
8” concrete block critical frequency of 80-160Hz

Due to the stiffness, it would seem that the block wall behaves similarly to a massive single leaf, at least in terms of the critical frequencies. Additionally the TL curve is roughly linear through 2500Hz, again perhaps behaving similarly to solid mass up to 2500Hz.

So that causes me to ask, "would the addition of RC channel to a solid concrete slab give us similar data as we saw with the addition of RC to the block wall?" Would the curves look similar?

Here is data from the NRC. This was thrown together quickly, so not precisely apples to apples but essentially we’re comparing a single concrete slab to a concrete slab with RC and drywall attached:



Data from the NRC IR-811.

Next I look at the data provided by Andre:



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.

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.

[rod gervais]

typically it should only cost around $3 sqft for the blown cellulose and keep in mind that the blown cellulose is adding around 3-4 lbs per sqft to your wall and is the highest rated insulation on the market.

Andy,

if you don't mind I am going to stick my 2 cents in here.......

The above is spoken like a true contractor - but not an acoustician.......

It is very true that blown cellulose is probably one of the highest rated insulations on the market - but it is NOT one of the highest rated isolations on the market.............

Insulation has only to do with temperatures - heat loss - solar gain - R values, U values, etc., etc., etc............

And when it comes to isolation - cellulose isn't anything special.......... as a matter of fact you can do just as good (or better) a job with standard fluffy fiberglass........... especially in the lower frequencies........

A few years back I had an interesting visit from someone in the cellulose industry who needed my approval to bid their product as an alternate for the insulation specified in sound walls for a 21 story hotel project - 440+ hotel rooms.....

We visited for about an hour - at which time I finally convinced him to release to me the actual test report/results for their product that he was using to claim a superior product......... (interestingly enough I had just spent some time reviewing their product (along with many others) in IR-761, and they are NOT a superior product in 761........ their numbers are not bad per se - but they are not superior........

I almost immediately figured out why their numbers as reported -(and I do not question even for a moment the honesty of their testing lab) were better than those reported in 761...........

Because of what I found - I also have serious concerns regarding THEIR moral compass.........

all of the testing in ir-761 is well documents - including the fact that their test samples were all 8' x 10'. This (of course) mean they are dealing with real world conditions - i.e.: 90% off all drywall installed has to deal with joints in the body of the wall. Joint and panel length have a direct effect on how rigid the wall assembly is as a whole - and they also introduce weak points in the mass of the wall..........

The cellulose company (on the other hand) only tested wall systems 4' wide by 8' in height......

Their test sample was design to create the most rigid specimen they could provide......... which would automatically move the numbers more favorably in their direction.

In this manner a company can tilt the scale in their favor - and seeing as they weren't releasing the data to the general public - who would know?

think about it...........

Rod

[rod gervais]

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

Fortunately for acoustics and studio builders, what you "believe" is irrelevant: all that matters is the science. Science works despite what you believe, not because of it. I can't understand how you can possibly even make such a statement, when scientific proof to the contrary is staring you in the face, in the above graphs and publications. Inserting a third leaf ALWAYS makes LF isolation worse, all other factors being equal,

MSM-walls.gif

- Stuart -

Guys,

calm down for a second and follow this in a rational manner - Ted is absolutely correct in what he is saying, and the chart proves it......

We think in terms of what is best - and then view how different from the best degrades a wall - and in that respect we also are correct.....

But Ted looks at the chart provided and sees a single wall on the left - add insulation to the wall and see an improvement - add a 2nd wall creating a 4 leaf assembly and see an improvement - remove one leaf inside and see an improvememt - .....

Thus his confusion on the statements being made - the chart clearly shows that going from a single simple wall with insulation to building a 3rd leaf would improve the wall's rating (in a perfect laboratory world) from STC 36 to STC 50 - which is an improvement on the original wall. Granted not the improvement that removing that inner leaf would afford (STC 57) but an improvement none the less.......

If you begin with a single leaf wall you cannot run the equation as if you began with an isolated frame double leaf (at which point adding the inner 3 leaf is a 7 dB reduction in isolation)........

It all depends on where the construction begins.

Sincerely,

Rod

[rod gervais]

Just a question: Are you the former colleague of Brian Ravnaas, of am I mistaken here?

Eric,

he is exactly the same person...... I am quite familiar with Ted's credentials........

By the way Eric........ hello my friend - how are you doing (not meaning to hijack the thread - but I miss my old friend).........

Rod

[xSpace]

"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]

Initially this is the phrase "Does anyone have data that shows a triple leaf makes the LF worse?"

Home schooled 101, poor question designed to get poor answers.

[Eric_Desart]

By the way Eric........ hello my friend - how are you doing (not meaning to hijack the thread - but I miss my old friend).........

Rod,

Thanks for this lovely inquiry. But as you likely expect that's difficult stuff for me.