Hanging Cloud from Isolated Ceiling

[dylan w]

Hi everyone,

First of all, thanks to everyone who has shared their expertise and wisdom. No way I could have built my studio without this forum and its awesome members.

Ok, onto the question!

Background
We've finished the construction on our barn studio build. Acoustic treatment is going well so far: superchunks in the vertical corners and along the floor, and broadband absorbers on the walls, have made a big difference.

Next step is a ceiling cloud, which should kill the floor/ceiling modes and bring the decay time into range. (I've experimented with actual panels to confirm the improvement.)

Problem
We built a floating pine ceiling under the original ceiling joists - 3/4" shiplap hung on furring channel and clips. Overall, I'm very happy with the isolation we've achieved, and I want to make sure we hang the ceiling cloud in a way that's safe but doesn't significantly compromise the isolation.

I don't like the idea of screwing coarsely-threaded eyebolts into the channel. Also, since the ceiling is already buttoned-up, I don't see how we could use nuts on the other side of the channel.

Plan
Drill holes in the pine ceiling, pass the eyebolts through, screw them into the ceiling joists, and caulk around the bolts.

Concern
Whether this will create an appreciable transmission path through the eyebolts from the outside joists to the inside.

The surface area of 32 eyebolts is very small compared to the whole ceiling, so I'm thinking that they couldn't radiate much sound into the room. I'll hang the clouds with chain, which should dampen any transmission from the eyebolts into the clouds.

Thanks in advance for taking a look - does this seem like a reasonable plan?

[dylan w]

Some details about the construction:

Ceiling
Inside: 3/4" pine shiplap
Mounted on furring channel and clips
Sealed with OSI SC-175
Insulated with R19 roxul
Outside: 1" pine boards over 2" joists

Walls
Inside: 1 layer, 5/8" type X sheetrock
2x4" staggered studs on 2x6" baseplate
Insulated with R19 pink fluffy
Outside: 1" pine boards over 2" joists

Floor
Space is on the second floor
Existing floor: 2 layers, 1" pine boards, over 2" floor joists
Insulated with R19 pink fluffy
Ceiling underneath: 1 layer, 5/8" type X sheetrock
Mounted on furring channel and clips

Isolation
Using iPhone dB meter, slow response, A weighted:
Outside traffic noise down from around 47 dB (no insulation or interior walls) to 28 dB.
Windows are the current weak point - will build 3/4" MDF removable plugs, with gaskets etc. Expect another 6 dB or so when windows are in place.

[Soundman2020]

Hi Dylan, and Welcome to the forum!

Congratulations on your studio build!

That said, I'm afraid to say it looks like you have shot yourself in the foot! There is no easy way around the predicament you have gotten yourself into.

This is one of the reasons why I'm always harping so insistently for members to do the COMPLETE design of their studio BEFORE they start building, taking every aspect into account, and making sure it will all work.

It's also the reason why I'm not a big fan of ceilings hung on RC (or on clips + hat channel).

OK, let's take a look at the two options you mention. In reverse order:

Drill holes in the pine ceiling, pass the eyebolts through, screw them into the ceiling joists, and caulk around the bolts.

Have you ever heard of this thing?:

tuning-fork-02--C-note-SML.jpg

Before electronic tuners and cell phone apps were invented, tuning forks were the only real method musicians had for tuning their instruments. You probably are aware of what they are, and how they work, but you probably don't actually have one. Get one! You can find them on ebay, amazon, and in some music stores. It doesn't matter which one you get, or what note it is tuned to: it's just to demonstrate the flaw in your line of reasoning.

So get your tuning form, tap it on the table, and hold it up in the air a couple of inches away from your ear. Can you hear it? Yes... but barely! It's very quiet, very faint, almost inaudible. Hold it a couple of feet away from your ear, and you cannot hear it at all. Now tap it again, then place the base of the tuning fork shaft on the table in front of you. Can you hear it now? You bet! Loud and clear. Because it transmits the vibration into the table surface, and the table then acts as a very efficient loudspeaker, transmitting that vibration into the air.

If you have a direct mechanical path from your cloud into the outer-leaf joists, then that's what you will get. Times 32, in your case! You mentioned that you want to hang your cloud on 32 eyebolts (I'm assuming it must be VERY heavy to need that many), so each and every one of those bolts will act as the shaft of the tuning fork does,, transmitting sound up and down the chains in both directions... sounds picked up by the cloud will get transferred (x32) up into the structure of the building, and sounds that are already in the building structure will be transferred down into the cloud.

The surface area of 32 eyebolts is very small compared to the whole ceiling,

... and the surface area of the base of a tuning fork shaft is TINY compared to the area of the desk... yet you hear the sound of the tuning for very loud, and very clear.

so I'm thinking that they couldn't radiate much sound into the room.

... yet tuning forks do radiate sound VERY clearly into the room, via that tiny, little thin stalk...

It's not related to surface area: it is related to acoustic impedance. A single vibrating bolt (or tuning fork) held out in the air won't transmit sound into the air, because the impedance of the bolt id not matched well to the impedance of the air. But the impedance of the entire ceiling (or table) is much better matched, so it transfers sound much more efficiently. The impedance of the bolt is also well matched to the impedance of the ceiling (or table) since they are both solids of somewhat similar characteristics. So sound is transferred efficiently from the bolt (or tuning fork) into the ceiling (or table), and then into the air.

Even if you could spray the joists with magical pixie dust causing them to not pick up any sound from the vibrating eyebolts, there's the other issue you mentioned:...

screw them into the ceiling joists, and caulk around the bolts.

How would you ensure that the caulk has the correct Shore rating and loading around the bolts, to prevent them from flanking into the inner-leaf ceiling: How would you keep them centered, and prevent them from moving slightly under chain tension, putting more pressure on one side of the caulk than the other? That's a tuned system, and it will only isolate if you design it to do so. You would need to get the resonant frequency at leas an octave lower than whatever frequency you calculate would be the lowest, traveling in those bolts and/or the joists.

I'll hang the clouds with chain, which should dampen any transmission from the eyebolts into the clouds.

Ummmm... Why do you think loaded chain will damp sound? There is a clear, solid, mechanical path down through the chain, from top to bottom. It's a solid metal path: each link in the chain is ins tight contact, under pressure, with its neighbors above and below. Did you ever play the "string telephone" game as a kid? With two empty coffee cans and piece of string joining them, knotted through a hole in the center of the bottom of each can? Stretch that string even a little bit taught, and it really does work as a "telephone". Even though string is floppy and soft, when you put a bit of tension on it, it transfers sound rather well. Your chains (or wire) are much more solid than string, and much higher density, so they will transmit sound far better than a string telephone.

Now for the other possibility you mentioned:

I don't like the idea of screwing coarsely-threaded eyebolts into the channel.

You say that you need 32 bolts to hang your cloud, so it must be really heavy. If you put too much weight on the hat channel, which is supported by the clips, you will overload the clips. It might be an actual structural overload, causing the ceiling to fail and collapse, or it might be less lethal, and just be a decoupling fail, where the clips stop floating and start flanking. In that case, the ceiling won't fall on your head and kill you, but the overload will trash your isolation, very thoroughly. Those clips are designed to work within a limited range of deflection. If you cause either too little deflection (by under-loading) or too much (by overloading), then they don't isolated any more, and they all turn into flanking paths, thus destroying your isolation. To check if this is the case, you will have to weigh your cloud (complete with the chains and bolts), then contact the manufacturer of the clips and give them that information along with the weight of your ceiling. They will be able you if your proposed method would cause structural failure, or just isolation failure. You could try to estimate it yourself, but that's a dangerous path. Put it in the hands of professionals. And get the manufacturer to put in writing his authorization for you to proceed with your plan, so that you have legal recourse if the ceiling does fall on your head. If you don't have something in writing, then the failure is on your head: figuratively, and literally! Your home-owners insurance policy will not cover structural failures that you caused yourself and were not duly authorized by the relevant authorities. You would be responsible not only civilly for the cost of rearing any damages, and the hospital bills of anyone injured, but also potentially for criminal liability too.

OK, so your two potions are both out the window. There is no way that either of those two could be made to work. Either you would trash your isolation in any of several ways, or you would end up with the cloud and the ceiling falling on your head.

Or you MIGHT get lucky, and it actually does work, by sheer chance and good luck! Any you might also win ever state lottery in the entire USA on the same day...

Whether this will create an appreciable transmission path through the eyebolts from the outside joists to the inside.

Yes it will.

Also, screw-in eye-bolts should never be used in the way you plan to use them (hanging heavy weights above a working area): that's unsafe. Check any manual or book on basic stage rigging, and you'll find very poor views of anything that simply screws in, with no mechanical stop on the other side. That would not be allowed in any theater, TV studio, or movie set. If you do use eye-bolts, they must be of the type that has a washer and nut on the far side of the support, and they must also be fully closed "eyes" (full circle, forged as one piece, not welded), not as open hooks.

So, it would seem the only feasible solution for hanging your cloud is to build a frame inside the room, that rests firmly on the floor on each side of the room, and has cross bars of some type spanning the width of the ceiling, from which you can hang the cloud. If you know where your inner-leaf studs are, then it might be possible to access those directly, through the inner-leaf sheathing, to attach your cross-bars. Of course, the frame and cross-bars would need to have dimensions suitable for supporting the weight of the cloud properly, which implies that it must be rated to support at least ten times the weight of the cloud. That's the safety factor that is often used for over-head rigging. In other words, if your cloud weighs 300 pounds, then the structure you build to support, and the hardware you use to hang it, must be capable of supporting a load of 3,000 pounds, at least.

I know you didn't really want to hear any of this, but it's the sad truth. I wish I had better news for you, but I don't. The cloud wasn't planned in from the beginning, you already built the ceiling, so you have painted yourself into the proverbial corner, with no way out.

The only other option (and the one I would recommend!) is to take down the ceiling and re-build it properly, with fully isolated joists that are dimensioned correctly to support the weight of the ceiling AND the cloud, together, and install the hanging hardware BEFORE you put the actual ceiling sheathing on.

So there are solutions, but not simple ones, and not the ones you proposed.

Sorry to be the bearer of bad tidings...


- Stuart -

[dylan w]

Hi Dylan, and Welcome to the forum!

Congratulations on your studio build!

That said, I'm afraid to say it looks like you have shot yourself in the foot! There is no easy way around the predicament you have gotten yourself into.

This is one of the reasons why I'm always harping so insistently for members to do the COMPLETE design of their studio BEFORE they start building, taking every aspect into account, and making sure it will all work.

It's also the reason why I'm not a big fan of ceilings hung on RC (or on clips + hat channel).

OK, let's take a look at the two options you mention....

Stuart, thanks for the detailed reply - this is really helpful. I appreciate the frankness, bad news or no!

The tuning fork analogy is great - makes a lot of sense - and likewise for the transmission through a taut line. So bolting into the outer leaf is clearly out.

So, a few more details:
The cloud(s) are actually not particularly heavy. I've specified 32 anchor points because there are 8 of them. Rather than hanging one large cloud, I'll hang (8) 2x4' panels - this way I can put them where they're modally and reflectionally most useful.

Each cloud will consist of a 2x4'x7.25" panel of Safe'n'Sound (12 lbs), framed by 1x6 lumber with the sides routed out (12 lbs not counting the routing). So, a thoroughly conservative estimate of the weight of each cloud and chain might be 35 lbs, spread over 8 sq ft.

As I think about it - why not just bolt the eyebolts into the shiplap?

The Whisper Clips we used are specified for up to 3 layers of Type X drywall, or a design load of 36 lbs load/clip. I estimate that the shiplap weighs 14 lbs over an 8 sq ft section, which would typically engage 4 clips (channel is spaced 20" or so on center, and 4' between spans). So 49 lbs over 4 clips is still significantly less than the 144 lbs design load, allowing room for the possibility that adjacent panels would engage the same clip (would still be important to make sure no two panels were too close). This seems well within design specs for deflection, though, as you say, good idea to contact the engineering dept of the company before installing anything.

Following the rule that a screw should penetrate at least 1.5x the diameter, a 5/16"-18 eyebolt would have enough purchase in the .6125-thick shiplap. This site specifies a 100 lb straight pull load for 5/16"-18 eyebolts, which includes a 4-to-1 safety factor. So a 400 lb pull load across 4 bolts, using a 10-to-1 safety load margin, would seem to do fine with 35 lbs.

With a quick Google, I didn't find any rigging manuals that had a specification for screw-in vs bolted fasteners - is there a guide you happen to like?

If screw-in is definitely out, it wouldn't be out of the question to drill and later plug small access holes to allow installation of a washer and nut on the other side.