Triple Leaf Effect Test Results

An ongoing question is what is the effect of triple leafs, and as part of that, if it applicable if one of the leafs is very massive. While doing research on a different topic I came across fig 8 in NRC BRN 217. The base wall is 140 mm (6") concrete block. Adding 1/2" gyproc on metal studs with fiberglass in the cavity raises the STC by 6 points, with a maximum TL reduction 2 dB @125 Hz.. Adding the same construction to the other side of the wall REDUCES the STC by 5 points, and REDUCES the TL at 125 Hz by 7 dB compared to the double leaf construction. Adding a third layer reduced the LF isolation and decreased the STC. Not bad for spending more money and time to get worse performance. :roll: A perfect example of how acoustics is not intuitive, and using a design consultant will save you money while geting you the best performance possible. Andre

Thanks Andre, I was pondering the use of a getting professional help for my space just last night. The amount of effort required to make this right and the knowledge to get it right is really hitting home. :shock: W

I have seen it referenced lightly on the forum, but never directly. What effect does a third leaf have if it is not very massive? How massive is enough to matter? Thanks! Scott

plus6vu wrote:

I have seen it referenced lightly on the forum, but never directly. What effect does a third leaf have if it is not very massive? How massive is enough to matter?

The example is of a light (compared to the concrete block) third leaf. You see the effects on the TL. The effect is a function of mass of the individual leafs and the spacings. This is getting into heavy math and physics. Sorry, but the best I can recommend is the 1973 Wyle report prepared by Sharpe. The formal document reference used is Wyle WR 73-5R. http://www.box.net/shared/jcaoavdc8g It is very technical, but is gold mine of useful information on sound isolation. It is a rarely found but highly sought after document. Andre

So is a three leaf a good assembly for a vocal booth or anything where low frequency loss isn't a concern?

xSpace wrote:

So is a three leaf a good assembly for a vocal booth or anything where low frequency loss isn't a concern?

Think about your question. Are the sounds you are trying to isolate at low frequencies? An electric guitar goes down to 80 Hz. A 4 string bass 40 Hz. Piano ~30 Hz. Are you isolating from such instruments? If you build it a certain way, I don't if right or wrong is the right adjective, the reduction in TL will be in the midrange area. That is getting into the lower range of alto singers. If you use a HP filter on your mic, that will introduce a phase shift starting about an octave above the cut off frequency. The short Andre answer would be yes, if low frequency is not a concern. The honest response is "when would you not need LF isolation?" and "If you do not design it properly, you can be pretty well guaranteed that it be screwed up." Further to that, a triple leaf requires greater mass (and cost) than a double leaf for the same isolation. Why do you want to triple leaf to begin with? Andre

Just pointing it out. The chart on figure 8 shows that the 3 leaf is higher in most all areas excluding the low. Since we are just talking and not spending money, I had to ask. Certainly lf is always an area that needs to be contained. But if it isn't, and there is a few dollars in the budget, and this area in the frequency range is the target, then it has its' uses. Like in a conference room?

xSpace wrote:

Certainly lf is always an area that needs to be contained. But if it isn't, and there is a few dollars in the budget, and this area in the frequency range is the target, then it has its' uses. Like in a conference room?

LF noise is a problem as a distraction. that is why NC curves were revised to go down to 30 Hz. Places like conference rooms were unacceptable due to low frequency rumble. What were you thinking of when you wrote "then it has its' uses?" What uses are you thinking of? Triple leaf is more expensive than double leaf. If not designed properly the TL will be reduced in the midrange. Please expand on this. Andre

AVare wrote:

Places like conference rooms were unacceptable due to low frequency rumble. What were you thinking of when you wrote "then it has its' uses?" What uses are you thinking of?

Looking at the graph for figure 8. That is what I am thinking about. The diamond character and graphed line, it climbs up above the other two...is this better or worse? Because it looks better, except in the low frequency area. Even that area rises rather quickly following the triangle char.

xSpace wrote:

Looking at the graph for figure 8. That is what I am thinking about. The diamond character and graphed line, it climbs up above the other two...is this better or worse? Because it looks better, except in the low frequency area. Even that area rises rather quickly following the triangle char.

Ever complain about a car that pulls up beside you with the sound system blaring that the hi-hat is shaking your car? Or is it the bass and kick drum? The low end is below your voice range, so it will not disrupt conversation according to the logic you are using. More importantly is knowing the spectrum of what you are trying to isolate from. Please give examples of where you think triple leaf would be of value acoustically. Andre

A conference room in a building on the 27th floor. People talking, no music, no cars driving by.

I have not seen any stickys on recognizing a 3 leaf system. The expense of creating a 3 leaf system that may work is obvious. What is not always obvious is knowing a 3 leaf system when you see it. There are probably 3 leafers that only someone with experience would recognize, along with flanking. Flanking is not always obvious either. Just some thoughts from someone who realizes he don't know everything. :) If I missed these stickys, please point it out. :oops: W

xSpace wrote:

A conference room in a building on the 27th floor. People talking, no music, no cars driving by.

I have had the pleasure of being in a conference room on 27th floor of a building in NYC. Sirens, traffic and the air handlers were very very obvious. I would say though, it was the external city noises that came in without a problem. Of course, the room was above the street with an unimpeded view of Grand Central Station. W

Studio Builder's Coat of Arms

:lol: :thu: :yahoo: Good one, André!!!! I hadn't seen that before. Spot on! :) - Stuart -

A conference room in a building on the 27th floor. People talking, no music, no cars driving by.

I think you would still have a problem with building noise in general. Buildings are not silent. They have air-conditioning systems, water systems, elevators, electrical systems, blowers, pumps, motors of all kinds, etc.. All of which produce low frequency noise. It might not actually interfere with the speech part of the spectrum, but you can still hear it, and it can be annoying. I used to rent office space in a building, right next to the elevator shaft, and believe me that low frequency rumble can be VERY annoying! Even though I could have a conversation in my office, or do a presentation in the conference room, without any comprehension problems, it was still an issue to have the constant muffled rumbling of elevators going past. - Stuart -

I think you would want to consider the whole freq spectrum. Doesn't matter if it is sirens, air handlers, subways etc. All the noise is unwanted whether a conference room or a studio. In the city, isolating from the structure and properly designed attenuation is required. Even though Electric Lady would stop tracking when the train would come by. :) Two leaf better than 3. W

Structure borne and airborne noise is part of the package with a mid rise building. In my reference building, there is not much interior noise moving around that is "annoying". It becomes part of the hearing environment from the time you walk in, not loud noises, just inherent to the city and concrete buildings. At the 300Hertz to 3500Hertz frequency range, I do not see why, in this situation, this three leaf isn't a good idea.

xSpace wrote:

At the 300Hertz to 3500Hertz frequency range, I do not see why, in this situation, this three leaf isn't a good idea.

What sounds are you trying to isolate? You have made your model a conference room. I THINK you are concerned with speech isolation. The STC system was developed for that purpose. The STC for the triple leaf wall in the example I gave is worse than the double leaf. You have discounted LF isolation on the grounds that it is part of the building environment. If the LF noise is acceptable, then the room is not concerned with acoustics to begin with. Andre

I am basing everything I say on the graph, labeled figure 8 from your first post. Why is a three leaf in this situation, my conference room at the 27th level, not a good idea? All the lines on that chart say that it is, as it pertains to speech.

xSpace wrote:

I am basing everything I say on the graph, labeled figure 8 from your first post. Why is a three leaf in this situation, my conference room at the 27th level, not a good idea? All the lines on that chart say that it is, as it pertains to speech.

The STC relates to sound isolation for speech. The STC for each wall is on the graph. The triple leaf wall STC is 5 points worse than the double leaf wall. It is all in the graph. Andre

The highest TL is represented by the black line on the chart is that right? That is my interest.

Here is my thinking, overall, Andre. Many many times we all see the "oh-my-GAWD, a 3 leaf is BAD, BAD, BAD!!!" Well, it is not something that we would invite into a studio build for sure. And the reason is, as best as I can say it, is the containment at low frequency suffers. And, it just costs more for this negative effect. Which also has a negative impact on a persons money. In the very few years I have tried to understand the facets involved in building better walls, my understanding of the standard STC is that it is antiquated. It is still a reference, but in my mind, it is hanging on to an old method. Using the whole frequency range that a human can hear seems like it is more important. That is what people do isn't it, when three layers of density and air and three more layers of density are used in the construction of isolation barriers? It is to make certain that ALL the highs and lows get isolated. I'm having some trouble figuring out this "figure 8" graph I am looking at, I admit:) But it looks to me that the overall frequency range is covered. It's contained. Except the very bottom end. Having that information I look into a wall that can do this and what good would this wall be in what environment. It seems like a conference room or any wall designed to contain human speech would be a good fit. Granted it may be a unique situation but it could exist, right? For me, this whole three leaf has taken on a life of it's own. Much like a floated floor:) It isn't something you will do every time, but it does have it's usefulness. Doesn't it?

AVare wrote:

It is very technical, but is gold mine of useful information on sound isolation. It is a rarely found but highly sought after document. Andre

This is great! I'll have to take some time to decipher it, but thank you very much for the document! I think it's going to answer more than a couple of questions for me. Cheers! :mrgreen: :mrgreen: Scott

Looking @ the graph again (great post Andre) I see that also adding just one leaf to the base wall will drop TL below 125Hz. The red line's the strongest below 125.... huh?? Does that mean a SINGLE leaf wall even outperforms a DOUBLE leaf wall below 125Hz ??

Ro wrote:

huh?? Does that mean a SINGLE leaf wall even outperforms a DOUBLE leaf wall below 125Hz ??

:roll: After all these years .... Tssss You start with a wall with one leaf and you have a curve rising with 6 dB/oct (theoretically). You add a second leaf and this 6 dB rise becomes theoretically 18 dBs in the first part, then goes to 12 dB/oct. In practice it rises with ca 11 à 12 dB/oct from the start. This is DIRECTLY related with the MSM as starting point. At the MSM your wall is worse. Hence also with a 2 leaf wall. That's indeed the reason that a single heavy brick wall easily beats double leaf drywall in the lows. Hence the art is to design double leaf in such a manner that this MSM is low enough not to bother. A triple leaf wall adds a second, higher frequent MSM making it worse than double leaf. All theoretically based on good walls, ignoring flanking and taking into account that triple (or more) leaf can behave rather unpredictable. But simplified for the lows/very lows Single: best Double: worse than single Triple: worse than double Quadruple: worse than triple And so on ...... As such working with single should be an option until a certain point. You need doubling of mass for a gain of theoretically 6 dB. It's still practical to double a 1/2' wall. Much less sensible to double a 1' wall and complete nonsense to double a 2'feet wall. Hence from a certain point you're forced to go to double leaf systems, simultaneously introducing this MSM problem, which you have to take care of in your design. Just mounting a resilient skin single gypsumboard panel with a cavity in front of a heavy massive wall and this massive wall will degrade in the lows at the MSM. The reason that a double leaf system BELOW the MSM becomes better again is just that there the double leaf wall starts responding back as a single wall. At the MSM frequency divided by roughly 2 (progressive thing) your mechanical double wall is acoustically/physically no double wall anymore but a single wall. Both leafs will vibrate in phase. In that range you calculate your double leaf system with the mass-law of a single-leaf system.