blown cellulose insulation & air cavity between double w

[dmjung]

By "constrained", am I correct in assuming your steel inner studs are already in place?

Yes, all studs are in-place...by "constrained" I was referring to situations where the gap between double walls was very small.

What we've ended up doing is using the blown cellulose on the outer wood stud walls and mineral fiber batts for the inner steel stud walls...the consensus at this point is we won't have a problem with the batts falling out. The inner drywall will be 2 layers of 5/8". The outer wall will be either a single 5/8" drywall and/or the actual outer wall of the house (hardi-plank). Green Glue is used between drywall sheets and on the studs...we obviously won't be able to tell if the GG made a difference, but the additional cost was minimal compared to the total project. (I'm taking pictures throughout the project and will post those if anyone is interested.)

BTW, only one layer of wallboard on the ceiling??!? For DRUMS??

Yes, well, I don't play very loud....usually. This is a concern...currently we'll be using 5/8" drywall with hat channels. Above me is the roof and beyond that is my in-laws. Cellulose will be blown into the attic area. I'm kind of anticipating we'll be putting up another layer of rock on the ceiling. My goal is to get is pretty far along, set up some drums and see where we are soundwise.

--David

[sharward]

. . . I don't play very loud....usually. This is a concern...currently we'll be using 5/8" drywall with hat channels.

Hat channels? Yikes. Read this and be afraid... VERY afraid.

[dmjung]

. . . I don't play very loud....usually. This is a concern...currently we'll be using 5/8" drywall with hat channels.

Hat channels? Yikes. Read this and be afraid... VERY afraid.

Afraid of what? I know that the hat channel won't perform like "real" RC.

It's curious that cheap hat channel hasn't been thoroughly tested for it's acoustic effects in various structures. It is definitely SOP for your average contractors/architects to want to use it for sound control issues...don't know if that's just ignorance, cost-cutting or they've historically found little real-world difference between hat channel and RC in most typical applications (eg flanking overwhelms any RC benefits.)

--David

[sharward]

It is definitely SOP for your average contractors/architects to want to use it for sound control issues...don't know if that's just ignorance, cost-cutting or they've historically found little real-world difference between hat channel and RC in most typical applications (eg flanking overwhelms any RC benefits.)

I'm going out on a limb here, but I think it's most likely ignorance (i.e., "they look the similar, so therefore they must be similar").

My garage has hat channel currently, but I think that was to reduce spacing to 16" o.c. on my 24" o.c. trusses. So, it might be SOP to use hat channel, but its purpose may be for something other than sound control.

Bottom line, if isolation is your goal, even if only partially or mildly, I would avoid hat channel and use the real stuff.

[AVare]

. . . I don't play very loud....usually. This is a concern...currently we'll be using 5/8" drywall with hat channels.

Hat channels? Yikes. Read this and be afraid... VERY afraid.

Afraid of what? I know that the hat channel won't perform like "real" RC.

It's curious that cheap hat channel hasn't been thoroughly tested for it's acoustic effects in various structures. It is definitely SOP for your average contractors/architects to want to use it for sound control issues...don't know if that's just ignorance, cost-cutting or they've historically found little real-world difference between hat channel and RC in most typical applications (eg flanking overwhelms any RC benefits.)

--David

Being direct, read the the thread including this link:

http://www.auralex.com/sound_isolation_rc8/RC_Page.PDF

It explains how RC works, and the importance of the sides and holes in the sides. After reading that, you will understand why regular hat channel by itself is not of use in recording construction.

Andre

[rod gervais]

It's curious that cheap hat channel hasn't been thoroughly tested for it's acoustic effects in various structures. It is definitely SOP for your average contractors/architects to want to use it for sound control issues...don't know if that's just ignorance, cost-cutting or they've historically found little real-world difference between hat channel and RC in most typical applications (eg flanking overwhelms any RC benefits.)

David,

I have no idea what your background is in the construction industry - but this is reality.

99% of contractors wouldn't know an isolated wall from a hole in the ground. They don't have a clue what the right products are or how to use them. That's why we have architects design buildings - and not contractors.

It is NOT SOP for architects to use hat channel in place of RC for sound control.

Any architect who does that should be shot and then have his liscense revoked (in that order).

What in the world makes you claim that this is SOP?

Perhaps you should check out "Architectural Graphics Standards" - which is published by the AIA (of which liscensed architects in America are members of).

It clearly indicates resilient sections (not hat sections) in areas dealing with sound isolation - and refuses to get involved in even suggestions for designs relating to studios - they suggest that architects bring on qualified acousticians before getting involved in design of that nature.

I would be very interested in where you got your info that this is SOP for architects, because it certainly isn't from the architects themselves.

Sincerely,

Rod

[sharward]

That's why you should be very afraid.

Thanks for contributing, Rod.

David, hopefully that clears things up for you.

[dmjung]

I would be very interested in where you got your info that this is SOP for architects, because it certainly isn't from the architects themselves.

Rod,

You are correct...I should have said "it seems to me" instead of "it is definitely SOP" and I initially had written it to refer to only contractors and added architects at the last moment while thinking about something else. My most recent experience with architects is with the one who had our new garage being built over a sewer line.

--David

[dmjung]

David, hopefully that clears things up for you.

You guys are killing me... I had already read those materials and threads on RC and hat channel awhile back and wasn't planning to use RC -or- hat channel. However, we ended up with HC on a couple of the ceilings in the house including my "music" room. (It's a long story.) Rather than bother with taking it down we left it in place and I told them to use some of the extra Green Glue on them before putting up the ceiling rock. (I know, naughty, naughty, an untested structure scheme.) I think there's supposed to be about 18" of blown cellulose up there as well.

My original question was about preserving the air gap in a couple of the double wall structures. The answer seems to be that the S in the MSM doesn't have to be "air" itself. True? Presumably anything less "springy" than air would perform worse and anything more "springy" should be better? (I couldn't figure out how to induce a vacuum between the walls. ) In any event, we're preserving the air gap.

My question at this point is where are the tests using HC as I'm curious about how inefficient it is relative to RC (or nothing at all.) I see tests using RC, but haven't seen anything on HC which is presumed to perform worse than RC (and I agree that it should.)

OTOH, it would seem that anything (could be additional structure elements or even just a construction method) that reduces the total physical contact area between structures should reduce vibrations being transmitted between structures at the contact points...or more likely its a function of total contact -pressure- between the structures instead of area? In any event, the RC is additionally efficient due to its "springier" nature and the HC less efficient due to its maintaining a stiffer link between the structures. True? Untrue? Untested/unknown? It's magic--don't bother trying to think about it?

I really suspect the HVAC will be where the isolation breaks down as I couldn't swing the idea of a completely separate system...

--David

[knightfly]

David, hat channel is designed to replace furring strips and is functionally at LEAST as stiff as a solid board. If you followed the link Sharward gave, I posted a horror story

http://www.recording.org/modules.php?na ... ic&t=22469

Had Bob's contractor had a CLUE, the correct stuff would have been used and the problem solved. As it was, we left Bob trying to choose between suicide and homicide.

That's enough "proof" for me, dunno about you... Steve

[dmjung]

If you followed the link Sharward gave, I posted a horror story

I had already seen the thread long before the hat channel was put up...since it was in the attic's direction it didn't seem worth the effort to remove it. The ceiling ended up as two layers of sheetrock and the attic has around 12" of blown insulation. As near as I can tell, I don't have any sound entering or leaving in the ceiling direction...even with 6 light cans and 2 hvac vents piercing the sheetrock. (I guess with the hat channel, I ended up with more than 12" over that particular room...so I guess it was good for something. )

In any event, except for weatherstripping the doors and tuning the room, it's done. I haven't lugged a set of drums up yet for a real test, but a stereo at fairly painful levels was only discernable at the door and in the garage underneath. I suspect if the house were completely silent (no HVAC or TV's running), then you could probably tell something was going on elsewhere...as it was, the ambient noise pretty much masked everything. The wall I was most concerned about seems to be completely silent with an ear stuck to it. I think if I can get the doorway under control (dual doors), I should be good to go.

--David

[knightfly]

Good to hear it seems to be working for you; BTW, one reason you may NOT be noticing problems from the ceiling with the hat channel - RC does NOTHING for low frequency isolation, it's mainly for mids/highs. So your drums won't likely sound more than a couple dB louder thru the ceiling than they would have using the real deal - your wide air gap is also helping things quite a bit, as will blown cellulose (another couple dB over fiberglass insulation in some tests)

Let us know when you get to the actual drum tests... Steve

[dmjung]

So your drums won't likely sound more than a couple dB louder thru the ceiling than they would have using the real deal

Probably so, but I wasn't planning to use RC anyway so it seemed rather benign at the time. (Plus that would be in the in-law's direction. ) Now if it had been on the walls or I had spec'd using RC, then it would have come down..

It is curious there doesn't appear to be any studies on HC usage--I assume it's because it has no audible effect and the RC does have a audible effect.

Let us know when you get to the actual drum tests... Steve

Absolutely....

--David

[knightfly]

Yeah, the reason for no studies on HC is that it's considered just a steel replacement for furring strips. Only place you'll see it mentioned in soundproofing is on sites that sell the RSIC clips; those, in conjunction with HC, are actually a bit BETTER than using RC... Steve