I'm not talking about floating joists (ie. resting on the stud walls) I'm talking about staggering the joists but hanging them on the ceiling rim joist - maybe there is no proper term for this but it seems to me like a staggered stud wall but horizontal. Those joists are connected to the floor above but only via the perimeter of the framing.

If I do clips and channel in between the joists (or a "staggered joist" as above) I guess I still need to decouple the stud walls from the ceiling structure? What clip/product is best for that?

Thanks!

That ceiling would be technically decoupled, but likely limited in TL the way a staggeres stud wall is limited vs. a double stud wall. The common connections will accomodate some flanking conduction and therein lies the limitation.

The walls are best dealt with via decoupled (double stud) framing rather than a product.

Even if the walls are decoupled (in my case from the foundation walls) how do you decouple them from the ceiling joists? (ie noise flanking up the stud walls through the ceiling joists)

DC-04 Clip: http://www.soundproofingcompany.com/products/dc-04/

Do you mean connecting the top of the walls to the floor above? If so, that is where the DC-04s come into play. That way your walls are secure and won't fall over, but are decoupled from the joists/ceiling.

Yep that's what I was referring to, thanks. I was vaguely aware if what they are but didn't know if they were required in this situation, or what the best products were at this time.

Thanks again Ted!

Always glad to look at good questions.

One small point of terminology clarification. Let's look at a wall.

Decoupling from an acoustics perspective means that the drywall either side of the studs can move independent of the other. Drywall on one side of a single stud wall does not move independent of the other side, therefore the two sides are said to be "coupled." Mount the same drywall on wood furring strips, and they are still coupled. Mount the drywall on a staggered stud wall, and the two drywall layers are now able to move independently, and are therefore acoustically decoupled.

Disconnection might be a term we'd use to describe what a double stud wall is compared to a staggered stud. Both are acoustically "decoupled," however the staggered stud wall shares a common top and bottom plate with both drywall layers. While Decoupled, the staggered wall isn't as disconnected as we'd like. The double stud wall is also decoupled and does not share a common top and bottom plate, and is therefore better disconnected.

The DC04 clip disconnects framing from framing. It doesn't decouple.

Hmm, is there really that much of a distinction? For example double stud walls are still connected by the flooring, at most you can say they are highly decoupled. Similarly I dont see how the DC04 clip performs disconnection, since the wall and the joist are connected by the clip :)

Or does the distinction have to do with plane changes?

The tests you are looking at are likely not for the channel you have. Most channel data is from the 80s when USG did testing. Most resilient channel benders refer to those tests but that's not at all accurate.

If you had access to data you'd find that the low frequency performance isn't good.

Have you considered recessing the clips and channel into the joist cavities:

http://www.soundproofingcompany.com/upload/rasied-blocking-detail.jpg


I think one would need to be very careful with their construction of this arrangement. All the load of the double drywall, clips and channel, not to mention anything attached to the ceiling will transfer to the blocking attachments. A couple of nails into the end of a SPF 2x4 isn't very strong. The nails might not shear off, but the blocking could easily blow out the sides of the wood fiber. If I were doing it like this, personally, I'd use some type of hanger (Simpson strong tie, etc.). Otherwise I think it's a good idea for saving height without full blown offset joists.

Yes, the two are distinctly different. That's why I wrote all of that.

A coupled wall is characterized by having a high resonance point. Simply decouple the two drywall sides and the resonance point drops substantially.

While the double stud wall is still connected to the floor, the TL of a double stud and a staggered stud are quite different. Assume same mass, insulation, cavity depth, the double wall performs better.

The clip substantially reduces the contact area of a top plate to a joist, and is also a much lossier connection.

I think one woudl need to be very careful with their construction of this arrangement. All the load of the double drywall, clips and channel, not to mention anything attached to the ceiling will transfer to the blocking attachments. A couple of nails into the end of a SPF 2x4 isn't very strong. The nails might not shear off, but the blocking could easily blow out the sides of the wood fiber.

#1 95% of installers would use screws.

#2 The 2x material won't blow out. Each block would hold 80 pounds of ceiling, however you could easily do chin-ups all day on a single blocking

Always glad to look at good questions.

One small point of terminology clarification. Let's look at a wall.

Decoupling from an acoustics perspective means that the drywall either side of the studs can move independent of the other. Drywall on one side of a single stud wall does not move independent of the other side, therefore the two sides are said to be "coupled." Mount the same drywall on wood furring strips, and they are still coupled. Mount the drywall on a staggered stud wall, and the two drywall layers are now able to move independently, and are therefore acoustically decoupled.

Disconnection might be a term we'd use to describe what a double stud wall is compared to a staggered stud. Both are acoustically "decoupled," however the staggered stud wall shares a common top and bottom plate with both drywall layers. While Decoupled, the staggered wall isn't as disconnected as we'd like. The double stud wall is also decoupled and does not share a common top and bottom plate, and is therefore better disconnected.

The DC04 clip disconnects framing from framing. It doesn't decouple.

Ted, thanks for pointing the distinction between the two. I've seen numerous questions and responses in many threads about the "decoupling" aspect discussed, while I get the feeling that often the "disconnecting" portion gets overlooked.

It took me a while when I first started my build to realize that you need both for good isolation.

Hi Floyd,

Every little bit helps, and both have importance, although both are quite different. You can gave a coupled wall disconnected from the framing, and a connected wall that is decoupled.

Touché :D

GetGray, I agree. Even using angle brackets would be sufficient. If you find ones ~5/8" you could use it to line up the blocks so your ceiling ends up true.

#1 95% of installers would use screws.

#2 The 2x material won't blow out. Each block would hold 80 pounds of ceiling, however you could easily do chin-ups all day on a single blocking
OOOOkay. You must know better carpenters than I do :). Would take some LONG screws to get decent penetration into that end grain, where the pullout capacity is lower. I'd have to flog my guys to make them screw it. Out with the nailguns they'd say :D.

But, I'm a chicken. Don't want my sky falling, hangers wouldn't hurt (done right). :D.

Still I like the idea in general. I have trusses so I *might* be able to fit some blocking in that rests on top of the lower chord.

Do you usually mud and tape the first layer drywall? I figure that I need to use acoustic sealant around the parameters, but not sure if mudding and taping are necessary.

GetGray: you can put the 2x4 blocks vertically or go to 2x6s if you want more security.

Do you usually mud and tape the first layer drywall? I figure that I need to use acoustic sealant around the parameters, but not sure if mudding and taping are necessary.

First layer does not get mud or taped.

Do you usually mud and tape the first layer drywall? I figure that I need to use acoustic sealant around the parameters, but not sure if mudding and taping are necessary.

No mud and tape on first layer. Just seal it up as you said. Staggering the seams will reduce maybe 80% of the potential issues. Alternating the ceiling / wall / ceiling / wall drywall will create a stair-step joint, which will take care of perhaps another 10% or so. The last 10% will be sealing up gaps in the drywall layers with sealant.

GetGray: you can put the 2x4 blocks vertically or go to 2x6s if you want more security.

Absolutely. If you can rest the blocking on that bottom chord as GetGray suggested, fabulous. In any event, using a big #12 coarse thread screw and pre-drilling the holes in the blocking will hold the blocking. The only remaining issue would be the thin plywood center of an engineered I joist. As-is it may not hold a screw as well as we'd like. You could beef up the center ply component by scabbing a second piece of ply to the affected area.

Ted,
Hopefully this is correct place to ask this question about soundproofing an existing HT ceiling. I currently have a smaller room (11x17) with low ceiling. I built room within room design and believe sound proofing is generally good with exception of low freq to upstairs. I think this is caused by a couple problems (1) bad null causes me to run bass a little hot (2) Likely a poor ceiling design.

I have attached crude picture of design but basically have joist cavitiy with two layers of safe n sound (I now know that pink would have been better). Joists of 2x4 of room in room ceiling have another layer of safe n sound. Below that is accoustical drop ceiling.

I did not want any drywall on ceiling for access to floor joists above.

After reading a number of your comments in this and other threads, I was wondering what your thoughts would be on removing the safe n sound from between joists on room ceiling and replacing with dw/gg/dw? I would place this inside the joists so not to lose any room height. I would not finish the drywall and leave the existing drop ceiling in place. Do you think this would be effective in removing a good portion of the bass that is shaking the upstairs?

Thanks
Darryl

Hi Darryl,

The lack of mass on your ceiling is the problem as you suspect. Can the double drywall be added to the bottom of the original joists?

The dropped ceiling tiles are neither sealed well enough nor have enough mass to create a real triple leaf. So no worries there.

You could absolutely leave the drywall unfinished.

Ted,
I cannot get to the original floor joists due to the joists for room in room. I cannot take down those joists as they are attached to walls. I would prefer not to install to bottom of room in room joists only because I would lose another 1.5 inches of ceiling height. That is what lead to thinking about inserting drywall between the joists.

If you recommend that inside the ceiling joists is a poor solution and I should stick to properly sealing the room by installing to bottom of HT ceiling joists, then I will revisit the room height issue.

Of course with either of those solutions, I have to determine if the 2x4 ceiling joists were designed strong enough to hold weight of double sheets of 5/8" drywall.

Thanks for your comments
Darryl

I would not hang double 5/8" on 2x4

I'm missing the function of these 2x4s. They don't hold up drywall. THe original joists could hold the support wires for the suspended ceiling... so what are these 2x4s doing currently?

It seems to me that the suspended ceiling could be removed. Then the 2x4s also removed. Apply resilient clips and channel to the original joists. Then finish the drywall as the final ceiling.

This would be much more isolating as well as taller. I assume I'm missing a piece to this which is why I ask.

Ted,
The ceiling joists were put in so that I would have a complete room within the room. The walls of the ht do not touch any other part of the house (except the floor). The two walls are connected via the ceiling joists so that they dont fall down.

I wanted to isolate the entire HT from the rest of the house. My execution was off because I overestimated the value of safe n sound and the accoustical ceiling tiles. Although working well for higher freqs, no substitute for mass (and green glue) for lower.

I was hoping to retrofit the room within room design without having to rebuild from scratch. I read a comment in a different forum from either you or Terry that suggested placing drywall peices on top of ceiling tiles to get extra mass. I was trying to take that idea a little further.

Unfortunately it may be too late for me to get a better solution. Just trying to make best of my existing mistakes.

I was also concerned about the weight which you seem to agree. Is there any value to using lighter drywall (ie 1/4") with green glue?

Your website (which is full of great info - wish I knew about it 5 years ago), talks about inserting dw / gg / dw to the bottom of the floor (inside the joists). This might be possible because I would be working with smaller peices and might be able work between ht ceiling joists. Would this give much value on its own? It would be a lot of work. I guess I could use the same idea and put a number of small strips to the bottom of the main floor joists. It should not matter if I use many smaller pieces instead of large 4x8 sheets as long as second layer overlaps the joints.

I hope I am starting to make some sense to you. Thanks again!
Darryl

Darryl, the primary job of the 2x4s is to hold up the opposite walls?

Ted,
Yes, sounds silly when you say it out loud. The other reason was to decouple / disconnect the ht ceiling from the joists of floor above (the rest of the house). This might have worked well (and made more sense) if that ceiling had drywall instead of accoustical tiles and insulation.
Darryl

Darryl I'd suggest removing the 2x4s, and installing DC-04 clips to connect the top plates of the inner theater walls to the original joists. This will disconnect them. They're still decoupled.

Then install resilient clips and channel to the original joists. This will keep the ceiling decoupled. Your goal of a room within a room will still be achieved. The isolation will be much higher as will the ceiling height.

Ted, I hear you. As painful as that sounds - your recommendation is the correct solution. I also understand that the other ideas I was thinking about will not work due to structure constraints (2x4s will not carry weight of required drywall).

Now that I know what the correct solution is, I can now determine if I have the desire and will to make the changes.

Thanks for your direction. You saved me from making another error. If I decide to fix this, I will contact you for supplies (green glue and clips).
Regards
Darryl

Now that I know what the correct solution is, I can now determine if I have the desire and will to make the changes.



That's funny!!! I say that about myself daily!

Ted, can you summarize what best practices are for HVAC soundproofing if a dead vent cannot be used? Is flex duct snaked (ie with bends) and the rest of the joist cavity filled with fiberglass pretty much all you can do? If so, does this represent a significant compromise? (ie. to the point where if might negate the other decoupling and soundproofing of the room)

Thanks!

Hi Andy,

Shoot me your email via PM and I'll forward you some articles on the topic.

Thanks - PM sent!

Hi Andy,

Shoot me your email via PM and I'll forward you some articles on the topic.

Ted could I get copies too? PM with email address sent.

Absolutely. Anyone is free to ask.

I would not hang double 5/8" on 2x4

I'm missing the function of these 2x4s. They don't hold up drywall. THe original joists could hold the support wires for the suspended ceiling... so what are these 2x4s doing currently?

It seems to me that the suspended ceiling could be removed. Then the 2x4s also removed. Apply resilient clips and channel to the original joists. Then finish the drywall as the final ceiling.

This would be much more isolating as well as taller. I assume I'm missing a piece to this which is why I ask.

Depending on the width of the room, you should be able to fit double 1/2" on your 2x4 ceiling. That means of course, that the 2x4's are resting on the top of the walls. Double 5/8" is heavier, so that might not work due to the added weight.

Yes but we need the weight

Strange...I was curiously looking for the original green glue thread and had to search a while back to find it. When I built my HT a few years ago the thread was always active with new posts almost every day. Is green glue still used to soundproof HT? has it been replaced with something better?

It is still very much in use. Take a peek at my thread and you will see tubes of green glue sitting in my open trash bag on one of the pages. Sticky, the sorta thin, stuff!

EDIT: Might as well just repost the pic here:

http://i113.photobucket.com/albums/n205/cybrsage/Home%20Theater%20Build/46.jpg