Effectively decoupled or not?

[rhythmrhymer]

Hullo Everyone, great forum!

Great books too, thanks for the recommendations.

I run a music store and school in Almonte, Ontario - just outside the greater Ottawa area. We've expanded and I'm taking this opportunity to relocate our drum instructor's room, isolate him from the rest of the school and give him some more elbow room.

The building was built a year and a half ago, and let me tell you. It's awfully painful watching contractors who say they've done it a thousand times install RC upside down! And that ain't all, either, but we'll move on...

We're graduating from less than 6' x 8' to a little over 11' x 3', so space is still a concern, and I have an idea that might buy me another 6" that I think will count. I propose to build a room within a room - sort of...

The south wall is exterior and not an issue.

The west wall is a staggered stud 2 x 8 common top and bottom plate with a bathroom for a neighbour - not a problem.

The north and east walls divide the room from our piano showroom, and our accountants office, so we don't want him counting triplets when he should be counting profits . I'll reinforce these with another layer of drywall (from the inside using GG), caulk, and then pink.

So. What if I build a double wall on the north and east sides, and where these meet the east and south, the only thing connecting them is two layers of drywall - the south and west with RC. I'll stop the (new interior wall) studs short by 1/2", and I'll tear the existing drywall off the south and westerly, and install RC (correctly!). The ceiling joists will float on the two new walls and a 4 x 4 in the other corner... please see the drawings with my sketchy Sketchup skills... (I forgot the pink and the doors in the drawings, but I won't when I build it!)

I realize I'll only gain about 6" by not building four interior walls, but that's half a whole foot, and we need to get as much as we can. Plus a double wall on the south would need another door (not drawn)...

Do you think this plan, done with great care, will effectively destroy flanking paths?

[rhythmrhymer]

Whoops. 11' x 3'. That's pretty small. I meant 11' x 7'. I should also clarify the drywall on the interior of the existing north and east walls will be removed and look like this...

[Soundman2020]

I guess you are going to want acoustic treatment in there too, right? so have you considered building those walls "inside out"? It might gain you another couple of inches, and this forum IS the home of the inside-out wall!

- Stuart -

[rhythmrhymer]

Acoustic treatment is in the plan for sure yes, but space and isolation are my primary concerns, in that order. Can you point me to a post that outlines what you mean by "inside out"? I tried the search engine but the engine replies "too general". Much obliged.

[snowdog99]

http://www.johnlsayers.com/phpBB2/viewt ... 7&start=30

Googled it, pretty good picture about 2/3's of the way down.

Basically, it's as described. You "flip" a standard wall around so the drywall is not inside the room, but outside.

So, from inside out you have:

Fabric covering studs/insulation
5/8" Drywall
Possibly green glue
5/8" drywall

Hope this helps,
Andy

[rhythmrhymer]

After a bit of thought, I think I know what you mean. That the existing wall should be my interior wall, and I should build the new wall as my exterior... I thought of that - it does gain space, yes. But first, that'll really make a mess of my beautiful (and operational) piano showroom. But more importantly, that wall is already locked to the south and west walls, so existing flanking paths negate the room within a room effect. No?

[snowdog99]

I'm going to make some assumptions based on my interpretation of the drawings you attached. Please correct me if I'm wrong. Hopefully I'll answer your questions at the same time, and be correct with the information. Again, this is just my understanding of the inside out wall.

1) The new wall you are building will be the interior wall, not the existing. Take a look at the close up detail pic you posted- "colourcorner.png." Now, assuming that the left side wall is the new interior wall.... Working left to right, you would have fabric, studs/drywall/drywall/air space/studs/drywall/drywall. Insulation between the studs in both cases.
2) This type of construction would turn your inner leaf into a large bass trap (effectively). Look at Lou's studio build where they actually start the construction of the control room. His is built using the inside-out method with fabric, and he didn't have to treat most of the control room with bass trapping etc.

I'll do you one better- here's the link. http://www.johnlsayers.com/phpBB2/viewt ... &start=270
If you read from that point on you'll see basically step by step what it takes to build an inside out wall.

So, you wouldn't be touching the existing structure really. However, you should do what you have to in order to remove what flanking paths may exist (if any).


My 2 cents,
Andy

[Soundman2020]

"Inside out" construction just means that on the inner leaf of your MSM wall, instead of putting the sheetrock on the side of the studs that faces the room, you put the sheetrock on the other side of the studs, the side that directly faces the outer leaf. The advantage of this is that you now have the stud space facing your room, and you can use that space for your acoustic treatment. It gains you over three inches of space on each side of the room, plus extra headroom in the ceiling, since you can now put a lot of your treatment in the gap between the joists.

The down side to "inside out" construction is that you do lose a little isolation, since your air gap in the MSM system is smaller than if you build the wall normally. But of course you could nudge your wall an extra inch inwards, so that you gain an inch of air gap, and lose an inch of room space. Or you could put an extra layer of sheetrock in there, so that your inner leaf is three layers instead of just two. Or both. It's a balancing act! Add layers or nudge walls, or whatever else you need to do, to get to the isolation level you need.

So if space is really tight in your room, an inside-out wall might be the answer.


- Stuart -

[rhythmrhymer]

Thanks Stuart.

I guess I should clarify: space is my primary concern after I've built the north and east walls, a double wall construction I plan to do like so:

gypsum / GG / gypsum / studs & pink / airspace / studs & pink / gypsum / GG / gypsum

The south and west walls are exterior or thick and unimportant for transfer, so in order to achieve a true room within a room without building double walls as above all round, is to disconnect the S & W with RC.

Take a look at this new drawing:

So you see, the inside room is sealed (tight as a drum) , and all flanking paths eliminated.

From what I've learned (and much of what I've forgotten), I think this is an excellent compromise for maximum isolation with minimum spatial loss, and really bad acoustics. Whaddyer think?

[rhythmrhymer]

The thing is, my goal is soundproofing over acoustics. We're running a school here, not a studio. The ceiling of this room will be a great help toward controlling rambunctious reflections, and I will treat the corners some, possibly put an area rug or two on the walls, but I do recognize it's still a box. But the question still remains - though allow me to rephrase it:

Is this plan defeating the purpose of the double wall, or is it a good plan? I had hoped to proceed today...

[Soundman2020]

Looking at the left side of your sketch, it seems to me that you have your inner leaf coupled to your outer leaf through the RC! That doesn't seem like a good idea.

- Stuart -

[xSpace]

It is an odd place but looks like it is right. Doesn't the RC decouple?

[rhythmrhymer]

Exactly my thinking. Doesn't the RC decouple...

[Soundman2020]

My point is, if you are only going to have RC on the one wall, then why go to the trouble of building a full separate stud wall for the other wall? The weakest link there is the RC wall, so that's the level of isolation you are going to get for the entire structure. So it seems pointless to go to the expense and trouble of building a double-stud wall for the other side. Why not just go with RC all around, if that level of isolation is all you need?

Or, on the other hand, if you really do need the better isolation that you get from a full double-stud wall, then why not do a double-stud for that wall at the bottom of the diagram too, where the RC is at present? Even an inside-out double stud wall there would be better than doing it with RC. You would have the exact same air gap, and zero connection through the RC, so it would HAVE to give you better isolation.

I just don't see the point of having a section of wall with good isolation that is connected to a section with not-so-good isolation.


- Stuart -

[rhythmrhymer]

So RC, you're saying, then is a connection of a sort. Yes? Makes some sense... However, let's just take one more look at this.

I will build a double wall all round if it is the final recommendation of experience on this here excellent forum. It's just gonna get tight in there, but it'll still be a step up in size from the room we're in now. And there's more, but I'll get to that in a minute.

Take a look at this drawing. Bleed through the south wall, is represented in green (green means go) - sound transfer through this wall is unimportant - goes outside. The red arrow is where transfers gotta stop, thereby the red light.

In my mind, the sounds gotta travel through exactly the same amount of msm no matter what path it takes - to get to where we don't want it to. Now given that you've elucidated that RC is indeed a mechanical connection and not a 100% decoupler (am I right in saying that??) that might not be totally accurate (?). Which if so, answers my question, "effectively decoupled or not".

If this is so, would you agree then that my approach would at least be 50% better than single wall construction with RC, and say, 75% (area) efficient of full double wall? I'm not trying to I just think that this is a good compromise (?).

Building a double wall also means I've got to build a double door (I didn't illustrate it, but there's a door in the south wall), and that's adding up to a lot of effort... not that I'm not up for it...

Anyways, sorry if this seems confusing, which it really isn't. I do appreciate your input!