Clarification of "leaves"

[Koggs]

Hi all,

Firstly i'd like to say thanks to everyone involved in this forum.

I am looking at options for isolating drums but wanted to ascertain if my understanding of the term "leafs" is correct.

1. Metal frame with drywall on each side and air gap/insulation between is considered as "2 leaf"

2. Room within a room constructed with the same method as above would be considered as "4 leaf"

Peace,

Koggs

[Soundman2020]

Hi Koggs, and welcome!

1. Metal frame with drywall on each side and air gap/insulation between is considered as "2 leaf"

That would be "coupled two leaf", since the framing members will easily transfer sound from the drywall on one side to the drywall on the other side. It is two-leaf, yes, but its coupled, and therefore not so good for isolation.

2. Room within a room constructed with the same method as above would be considered as "4 leaf"

That would be 4-leaf, yes, but more accurately it would be a pair of coupled 2-leaf walls, and would likely not provide good isolation, especially in the low end.

Your best bet is a fully decoupled 2-leaf system: two frames, each of which has drywall on only ONE side.

This might help clarify:

2-leaf-3-leaf-4-leaf-STC-diagram--classic2-GOOD!!!.gif

- Stuart -

[Koggs]

Thanks Stuart,

Low end is the target

[Koggs]

Hey Stuart,

In that double leaf assembly pictured above would there any advantage to using plasterboard of differing thickness and density (on the same side)with green glue between them?

Cheers

[knightfly]

Hey Koggs; I've not been on here for a few years, but hopefully I can remember enough to help

First off, several of your questions could be answered here
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=4310

Not trying to be mean, I just fully understand what mods go thru trying to answer the same questions several times a day - one of the reasons I left is because doing just that left me ZERO time for any personal projects. That's why I STARTED the reference section in the first place; and it helped, but there were STILL too many people wanting to be "spoon-fed" for free...

Now that the "snarky" part is over, you asked about "using plasterboard of differing thickness and density (on the same side)with green glue between them?"

Assuming two different thicknesses of plasterboard are of the same brand, etc, they should automatically be different in density - if they are touching but NOT glued (green or otherwise) then each layer would have a slightly different RESONANT FREQUENCY, which is partially dependent on the plasterboard and partially on the frame characteristics - lightweight steel studs, for example, will be more flexible than wood, and therefore de-couple the leaves from each other a bit more (this = BETTER) - because the funtion of a wall is to BLOCK sound, more mass and LESS coupling will both make it harder for sound to get through.

I've still not messed with Green Glue, may or may not in this lifetime; so take this as a "SWAG" - aka Scientific Wild-Assed Guess :=) People tend to use less than a continuous coat of GG because of the cost, so that MIGHT have a different result than a COMPLETE coat between layers of plasterboard - the partial connections should leave each layer of the leaf a little more "autonomous", as in, more likely to keep some of their OWN resonant frequency; I would think this is a GOOD thing, because you'd still get the elasomeric decoupling between layers, and MAYBE a bit more effect from two DIFFERING resonances which would BROADEN the resonance area -

Any time you can have DIFFERENT resonances in components of a wall system, you SHOULD - if ANY of the components of a mass-air-mass (aka mass-spring-mass) system have the SAME resonance, that's the frequency that's gonna come right through. One example of this is (WITHOUT the help of elastomers) is doing ONE side of a 2-leaf wall with TWO layers of 5/8" plasterboard, and the OTHER leaf with THREE layers of 1/2" plasterboard (or 2 layers of MDF) - Nearly ANYTHING with a different mass.

This ensures that no SINGLE frequency gets a free pass - THAT flaw is one that'll get noticed quicker than almost ANYTHING, because it's so OBVIOUS a disturbance.

Another thing that's maybe NOT so obvious (til it bites you in the ass) is making sure you don't inadvertently COUPLE 2 frames of a double-framed wall for some reason - I remember reading an experiment several years ago, they started with a 2-leaf solid concrete wall - IIRC, the individual leaves were 4" and 6" thick, maybe 12" apart; and their ONLY connection to each other was the earth - the wall was tested, and obviously tested REALLY good - I don't remember the actual TL values, but basically drums and/or screaming vocals couldn't be heard on the other side -

Then, they core-drilled the inner wall, big enough to push a wooden dowel thru the inner wall and tight against the outer wall, and epoxied the inside in place - the re-test allowed NORMAL CONVERSATION to be heard on the other side. (Obviously the dowel was drilled out after the test :=)

I've been studying acoustics/sound control off and on for nearly 40 years and couldn't tell you where I read that, so please don't ask for a link - my point is just that in acoustics and sound proofing, there is NO SUCH THING AS TOO MUCH ATTENTION TO DETAIL (or too much study)

Anyway, my intent was NOT to hurt feelings - only that there's a LOT of useful info ALREADY written here, and the more of it you read the less likely you'll be unhappy with your build... Steve

[Eric Best]

Knightfly, Welcome back, great to see you here!

[TomVan]

And I just assumed someone spammed the thread when I saw your avatar.

Good to know you are still kicking
T

[almaelectronix]

Hi everyone, since you are talking about leaves maybe someone can help me..

I ve got a 6x4meters wall , 23cm thick, made of bricks on each side and filled with stonewool inbetween.
it has several horizontal and vertical concrete beams which go through both walls and insulation and connecting the whole system.
Is this still a 2 leaf?

i ll go room in a room too so my plan was to add air and then mass in front of this wall, but if its 2 leaf already then maybe not the best option, so am trying to find the best possible solution for this side.

i mean if its a 2 leaf it would be best to add the drywall mass directly on one side of the brickwall but then i can not decouple for the room in a room..


attaching a quick sketch
any suggestions?

thanks!

[almaelectronix]

any thoughts ?

[Soundman2020]

any thoughts ?

There is an announcement at the top of the forum about what to do to assure getting as many responses as possible.
The announcement leads to this post (click here). Actually, several people on this forum who are experts will most likely not reply if you don't do what is written in that post. Many others who are very helpful, will probably not reply out of respect for the moderators' wishes.

That said, what you describe is technically a fully-coupled two-leaf wall. It is two leaves in the sense that there are two "bunches" of mass separated by an air gap, but those two "bunches" are very well connected to each other mechanically, and therefore acoustically, so in reality that wall acts almost like a single-leaf. There might be some internal resonance in those cavities, sure, but they won't be working in your favor, and I would treat the wall as though it were a single leaf.

I mean if its a 2 leaf it would be best to add the drywall mass directly on one side of the brickwall

That would make practically no difference at all for isolation. You have about 23 cm of concrete and brick, which translates to a surface density of roughly 550 kg/m2. The surface density of drywall is roughly 10 kg/m2 for a single sheet. So adding a layer of drywall would increase the mass by barely 2%. Considering that you need to DOUBLE the mass to make a useful difference in isolation (maybe 5 dB, in the real world), you can see that adding a layer of drywall over brick or concrete basically does nothing at all.

... but then i can not decouple for the room in a room

There's no problem in your case. There's a huge amount of mass in the bricks, and the wall is basically single leaf, so it's not an issue.


- Stuart -

[almaelectronix]

Soundman thank you for your time. You are right I had to read the instructions first. Really sorry about it.
I usually search and read before posting anything, I missed that.

I am really thankful for the time and the effort you all put into it. Some great information shared in here.
I also know time is really hard to spare, myself being a father of two, working man and active musician, so I can understand.

I am reading the forum some time now, as a guest, mostly for educating myself as I am a musician and producer of my own music.
It is only the last days I decided to join as a member as I am planning to build a studio for recording/mixing my music.

I have a room of 53m2 on a groundfloor in Athens - Greece and I am planning to use it mostly as a control room for mixing. Also rehearsing with my band once a week.
Initially it was a 90m2 room which then was divided with this double brick wall I mentioned earlier, the rest 37m2 are being used as a shop selling photo related stuff.
Next to the other side of the room there is also a shop selling shoes.
And that's it, all the other sides are open space and no house closer than 10 meters.
Oh there is also a basement under almost 60% of my groundfloor, which I now use as a studio but I will leave it when the upper one is ready.
I live on the 1st floor with my family, and 2nd floor is empty for now.

Most of the walls are double brick without insulation in between so one leaf.
Just this one wall I posted earlier has insulation so I needed to confirm the 2leaf actually working as 1leaf which was what I thought too. Thanks again for confirming that soundman.

I am now reading Rod Gervais book and this forum for deciding how to proceed in order to not disturb my family and nearby shops and next to achive good acoustics for mixing.
Two years ago I built a studio on the basement (details posted on another forum) which was great but unfortunately I am kicked out, although we had another deal, but anyway.
So for now I need to take down some middle walls in order to have one big room as I want.
Also trying to keep some money for starting my studio..

Thinking of starting a new thread with detailed plans , photos, measurements, etc, when I am ready to go!

[knightfly]

Eric, thanks; I probably won't be around much, I'm on my 3rd "new life" since leaving, sorta - I'm hoping the "9 lives" thang is implied by my avatar (now long dead, unfortunately - there went THAT plan ) I hope life's going well for you...

Tom, I LIKE spam (if it's FRIED right ) I noticed your post count and wondered what you'd been up to; then I checked out your studio website, and HOLY CRAP, got more answer than I'd bargained for - congrats and envy all rolled into one

I finally retired from my day (rotating, actually) job almost 6 years ago, been spending a LOT of my time on projects that will hopefully allow me to stay on my 10 acres til somebody decides it's time to "pat me in the face with a shovel" - most projects these days involve one or more of tractors, welders, and/or custom implements that will let me sit on my ass and wiggle hydraulic levers - the main goals are staying lazy while looking like I worked really hard (oh, and inventing stuff that friends say won't work so I can watch their faces when it DOES )

Anyway, got a new welder (makes 5 or 6 now) that's crying for its own cart - so I'll be working on THAT after supper - I still play keys and guitar now and then, keep telling myself to actually put it into my SCHEDULE so it happens more often.

Stay well guys... Steve (AKA "Spam what am a HAM"