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PostPosted: Sun Sep 21, 2008 3:28 pm 
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Question for the acoustic experts: When is a "leaf" no longer a "leaf"?

I guess I'm a bit confused about the concept of leaves. I think I have the basics right: I've read stacks of recommendations here that the ideal thing is to have two and ONLY two leaves in your studio, ie, "room within a room", where you have one bunch of mass on the "inner" wall, separated by an air gap, and then another bunch of mass on the "outer" wall, and nothing else.

But it seems to me that the only way you can REALLY do that is to construct a free standing building on tall stilts in the middle of a field to contain your inner room, with nothing at all but open air around it! It doesn't seem possible to do that as part of an existing structure. Either that, or I'm missing something here....

My basic concern is that in the design for my studio, I think I'm stuck with the horrible crime of having a third "leaf" that I can't do anything about. And a forth one too, probably... And that concerns me. Should I be worried about my "extra leaves"? Do they matter?

Look at the sketchup view below, and you can see my gross approximation of a control room (in the middle) and a live room (on the right) that I'm about to start building in my minuscule garage. Plus, the laundry (on the left), the kitchen (behind the control rooms, bottom of pic) and the neighbors garage (top of pic) on the other side of the brick wall.

The way I see it, ALL of those rooms are basically "third leaves" from my point of view sitting in the control room!!! Or am I wrong about that? To me, I see another bunch of empty air, followed by another bunch of mass on the other side, in all cases. In the case of the laundry, there is yet another room out to the left ("guest room"). That would make leaf #4

So, I'm assuming that what makes these "leaves" not important, is the large chunk of empty air between the walls. Is that a good assumption, or are they still "leaves" anyway? If so, what should I do about them? And if they are not important, then how big does the "air space" have to be, before it no longer is really a "leaf" at all, or at least, not enough of a leaf to be important?

I'm still trying to get my head around these concepts. It's not that easy to grasp some of the stuff about acoustics and pesky sound waves and things!

I'd really appreciate comments by the experts on my design, too! Am I really accomplishing the full two-leaf "room within a room" concept with my design? What could I do to improve it? Where am I going wrong?

Here's a link to my thread:

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=11122



Stuart


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PostPosted: Wed Sep 24, 2008 1:32 pm 
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PostPosted: Wed Sep 24, 2008 4:53 pm 
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When "leaves" are structural connected, it becomes one leaf.
okay, that didn't help...

Sometimes you've gotta work with what you have. If that means multiple leafs, so be it.

Your exterior wall is one leaf. Building a double stud wall (2 leafs) within (and relative close to the existing leaf) the structure will create multiple leafs.

as per your drawing: the north, east and south walls are multiple leafs. You might also build the doublestud wall flush against the existing walls. This way you'll "beef up" the exterior and have one leaf to separate the rooms. (get it?) So, why not beef up the exterior walls and add one leaf wall. Keep the double stud walls which separate the CR and TR, also keep the west wall as double.

hope you get the picture. But again, if it's 3 leafs you have to build; do it. (don't worry TOO much about multiple leafs, live with it if it's the case)


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PostPosted: Wed Sep 24, 2008 10:24 pm 
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Thanks Ro! Appreciated!

I guess you can't see it too clearly from the above image, but I think I'm already doing what you describe. The "outer" stud walls are actually going to be built inside-out (is that the right term?). In other words, the sheetrock is flush up against the existing walls, probably with green glue or something like that in between to seal the gap, and the framing is on the INSIDE of that (or in-between it), just holding it in place with cleats or something. I still need to figure out the construction details.

One idea I have here is to follow what Sharward did: cut panels of sheetrock to fit between the framing, pressed up tight against the existing outer wall so it basically becomes one wall, held in place with cleats on the studs, and everything sealed tight with some type of caulking.

Is that the right idea? What I was trying to accomplish with that is beef up the outer wall by sticking 3 or 4 layers of sheetrock directly to it, without building another leaf. Am I on the right track here?

Here are some close-ups of what I have in mind:

First, a general view from overhead the wall between the control room and the live room.

Then a shot from the same place with only the framing and sheetrock.

And finally without the framing that is supposed to hold the sheetrock in place. It's not very clear from the pic, but that is four layers of sheetrock, pressed up tight against the brick wall.

Is this the right idea? If so, any suggestions on how to attach the sheetrock firmly and still keep a tight acoustic seal? This is earthquake territory where I live. Big time. It needs to be tough.


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PostPosted: Thu Sep 25, 2008 3:49 pm 
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Soundman2020 wrote:
I guess you can't see it too clearly from the above image, but I think I'm already doing what you describe. The "outer" stud walls are actually going to be built inside-out (is that the right term?). In other words, the sheetrock is flush up against the existing walls, probably with green glue or something like that in between to seal the gap, and the framing is on the INSIDE of that (or in-between it), just holding it in place with cleats or something. I still need to figure out the construction details.
First of all; GG (green glue) is NOT a sealant.

Quote:
One idea I have here is to follow what Sharward did: cut panels of sheetrock to fit between the framing, pressed up tight against the existing outer wall so it basically becomes one wall, held in place with cleats on the studs, and everything sealed tight with some type of caulking.
That's indeed the idea I had in mind.

Quote:
Is that the right idea? What I was trying to accomplish with that is beef up the outer wall by sticking 3 or 4 layers of sheetrock directly to it, without building another leaf. Am I on the right track here?
Yes, as long as the goal is to add mass to the exterior wall.
BUT, if it's solid rock already I wouldn't worry about it too much. Adding GB would not even double the mass. So, might even wanna leave it like it is. You can stucco the wall if you want. That might close it up a bit better and will save you about 3dB.

So like this: stucco/plaster the exterior wall on the inside.
Add a 2nd wall in front of the exterior wall (not touching ofcourse) by building a frame stuffed with wool and add GB on the inside of your new rooms. (unless you wanna make inside-out walls ofcourse. But then you'd have to add wool another way)


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PostPosted: Thu Sep 25, 2008 11:06 pm 
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Thanks Ro!

So using Green Glue between the first layer of sheetrock and the brick wall is not a good idea? OK. I'll just stucco the wall then, instead. I thought green glue would help to "unite" the sheetrock to the wall, helping them act together instead of separately, but if I understand what you are saying then that's not what it would do here?

The reason why I think I need to beef up that wall is because it is just one single layer of brick, and it is the dividing wall between my garage and the neighbor's garage. It is actually the property divider, and it is the wall I am most concerned about. I want to block as much sound as possible through that wall. I thought that layering sheetrock on top of that wall was the best way to accomplish that? I figure that four layers would help a lot, but from what you say, it seems like it won't really help much at all? What should I do with that wall then?


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PostPosted: Fri Sep 26, 2008 3:40 pm 
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Soundman2020 wrote:
So using Green Glue between the first layer of sheetrock and the brick wall is not a good idea?
I'm not sure about the effects of GG between GB and stone. Haven't seen tests on that, but my guess is that is would not work quite well.
It's not worth the trouble. Your wall is already heavy, adding a pane of GB would have little effect.

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OK. I'll just stucco the wall then, instead. I thought green glue would help to "unite" the sheetrock to the wall, helping them act together instead of separately, but if I understand what you are saying then that's not what it would do here?
okay.

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The reason why I think I need to beef up that wall is because it is just one single layer of brick, and it is the dividing wall between my garage and the neighbor's garage. It is actually the property divider, and it is the wall I am most concerned about. I want to block as much sound as possible through that wall. I thought that layering sheetrock on top of that wall was the best way to accomplish that? I figure that four layers would help a lot, but from what you say, it seems like it won't really help much at all? What should I do with that wall then?
In comparison to the wall, adding GB has, as I wrote, little effect. Unless you plan to add a lot of sheets to the wall.

A brick wall weighs about 2300kg/m3.
GB weighs about 700kg/m3
So brick is about 3 times as heavy as GB.

Having a 4" brick wall is, in weight, the same as (4" / 5/8" x 3) = about 20 sheets of 5/8" GB. Thus, to double the mass you need A LOT of GB.
Adding 4 sheets is about 20% of the mass of the wall's weight. Not too much (in dB's) if you'd ask me.

Dunno about how strong your ground/foundation is but, why not build a brick inner wall? That's teach'm :)
(although you want some more flex in your walls, GB swing more than brick)


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PostPosted: Fri Sep 26, 2008 4:23 pm 
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Wow! that's actually pretty good if I don't need to beef up that wall! It will save a lot of time, money, and even gain me a couple of precious inches of space!

I'm going to look into that idea of a second brick wall, too. It might just be possible. Not sure what code says though, about building right next to the divider wall. I'll have to find out.

One more question: Would it make any sense to go for 4 or 5 layers of sheetrock (GB?) on the inner leaf, instead of just 3? I'm planning to build the inner leaf "inside out" (GB on the "outside", facing the brick wall) because of my severe space limitations, so I figure I might as well add a bit of that extra mass that I'll be saving from the other wall, if that one doesn't need it.

Also, right now I'm getting about 8 cm (3 inches) of air gap between face of the inner wall and the brick wall. Is that good enough? Do I need more? Would it make a big difference if I dropped that to 5 cm (2 inches)?


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PostPosted: Fri Sep 26, 2008 4:52 pm 
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Quote:
I'm going to look into that idea of a second brick wall, too. It might just be possible. Not sure what code says though, about building right next to the divider wall. I'll have to find out.
Maybe ROD could comment on this topic as he clearly knows a lot more about these things than I do. Hell, for all I know I could be completely in the wrong :shock: haha

Quote:
One more question: Would it make any sense to go for 4 or 5 layers of sheetrock (GB?) on the inner leaf, instead of just 3?

3 layers of 5/8 is good. Doubling mass is a plan. That means 6 sheets, but thaz a lot. What's your goal?
Have you measured the existing construction for soundtransmissions yet?

Quote:
I'm planning to build the inner leaf "inside out" (GB on the "outside", facing the brick wall) because of my severe space limitations, so I figure I might as well add a bit of that extra mass that I'll be saving from the other wall, if that one doesn't need it.
As John did some great in-side-out wall designs, I'm not a big fan of'em. Sure, it saves space and creates a great way of having absorption in your room.
The gap between the 2 walls need at least some absorption, else you might end up with a drum-skin like wall. Sound inside the cavity should be absorbed if possible.

Quote:
Also, right now I'm getting about 8 cm (3 inches) of air gap between face of the inner wall and the brick wall. Is that good enough? Do I need more? Would it make a big difference if I dropped that to 5 cm (2 inches)?
8cm (3") is good. Is that INCLUDING the frame depth? If you're building in-side-out than, yes, you'd be better of with a wider gap.

You need atleast 1" (the space to seperate walls). Having it framed witch 4x4 for example will make the gap 5" in total. But with in-side-out, it's "just" 1" (2,5cm). That's not too much.

You see, that's another reason why I'm not a big van of In-Side-Out walls :)

(hmm, confussing post.. haha)


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PostPosted: Fri Sep 26, 2008 11:52 pm 
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Naah, not confusing at all! I'm starting to get the picture from you guys already. And I REALLY appreciate your help!

Quote:
Have you measured the existing construction for soundtransmissions yet?


Not yet. I'm still in the process of clearing out several years accumulation of "junk" in that garage. I could measure as it is, but there is so much stuff in there, including a set of cupboards all along that brick wall, that I don't think my measurements would give a good picture of what is actually happeneing with the room itself, acoustically. It will be a few weeks still, before I can get it down to bare bones and take some serious measurements.

By the way, what is the best way to measure? I'm guessing that I should just pump out pink noise at maybe 100 dBc inside the room, then measure at several points outside, beyond each of the walls? Or should I be more detailed, and do this with a tone generator at a range of specific individual frequencies? Say 1/12 octave, at least for the low end up to around 300 Hz.?

Do you know of any white paper or set of instructions on how to do this measurement correctly?

I'm guessing that Rod's book probably explains it, but my copy has STILL not arrived from Amazon (and I ordered it three weeks ago!!!), so any advice you can give in the meantime would be welcome.


- Stuart -


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PostPosted: Sat Sep 27, 2008 9:54 am 
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HOW LOUD are you:
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=3231

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PostPosted: Sat Sep 27, 2008 10:30 am 
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Quote:


I guess this is my fault for not sticking to one single thread! The answer is in the first post in my main design thread, here:

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=11122

"How loud am I? For mixing, I like to keep it to manageable levels, around 80 to 85 dB(C) (yes, I do have a sound level meter, and yes I do use it), maybe 90 peak. For tracking, it’s another story: If the drummer wants to smash out 115 dB, then that’s how loud I am, even though I don’t want to be. I value my ears. Which is why I have this nutty notion that I’d like to squeeze both a live room AND a control room into this matchbox-sized garage, with at least a few dB of isolation between them, so that my ears don’t wilt and drop off when the drummer gets inspired. "

That's why I figured 100 dB for the test would be a good starting point.

Maybe we could shift this discussion back to my main thread again, in order to avoid fragmenting issues about my studio, and keep it all in one place? Sorry for screwing up like this!


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