Air "bag" between ceiling and plaster ceiling is causing rattling noise

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Rodolfo90

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Hello,

I'm new to this forum, and I've come looking for some advice on the matter. So hello everyone and thank you in advance for you advice and help.

So here's the thing. Me and a group of people are building a recording studio, sort of home but we've also invested money in it some it's decent. I'll be posting some pictures later if possible but I'll try to describe for you in hopes in can give you a better idea of the problem:

The recording booth persay is about 6'x11' more or less. About 60-70% of the wall area is covered in acoustic foam. The real problem here isn't whether or not the foam is working; as the title says there's a sort of air bag (cavity between the ceiling and the plaster ceiling) which creates a sort a rattling noise whenever we make a loud sound such as clapping or even the snap of fingers (around the center of the room). The real ceiling has an angle and the plaster ceiling is flat, so you can imagine more or less how the shape inside really is. The shortest distance between the plaster ceiling and the real ceiling is more or less 1' 5"; the longest distances being about 3' 4".

My theory is that this shape is creating the same effect the body of acoustic guitar creates. The sound waves go through the plaster, through the air bag and then crash against the hard concrete of the ceiling then back to the room. In the way it either reverberates or gets amplified. Another theory is that the plaster itself or the wires that hang in that cavity are vibrating. Either way I need to find a way to get rid of this rattling.

So I need ideas guys, anything you can share. I was thinking of covering the ceiling with acoustic foam, hanging sort of bass traps or panels, or even drilling holes in the ceiling! I believe the latter might intensify the issue though. Hanging bass traps or panels makes more sense to me and the people I've discussed the matter with, but I'd like to know what you think. We were thinking about building a few sort-of bass traps/panels from the ceiling; not sticking them to the ceiling but actually hanging a few small ones or 3 or 4 big rectangular ones.

Please let me know what do you think of this idea. Perhaps I just said something very stupid, let me know! If you have a better idea you would save my day. In the case this bass trap/panel idea actually makes sense I would really appreciate it if you could perhaps leave a few links or instructions on how to design this traps/panels. I know the essentials and I know there are a ton of DIY videos but for what I've seen these specific designs are specifically for absorbing sound and create silence basically. Can you give a different use to these panels ? I mean, I'm sure that by changing their properties you can get different results I.E. size, filling material, frame material, width etc. But, what are my guidelines ?

Do I want this panels to absorb or to reflect? In either case, what frequencies are we talking about? What materials, shapes, size, width will I choose for the desired results?

Again, thank you very much for your time. All the advice you can provide will be helpful,

Rodolfo.

PD: The rattling sound I'm talking about sounds more or less like the "Bathroom" filter you find in many recording software.

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Bathroom filter found in what?

Sorry, I am in the middle of a session. I only posted to get updates. Back to respond later. Much to talk about....
 
Not following this at all .... "Airbag"?? Do you mean a resonating cavity between the ceiling and concrete surface above? If so, can you just remove the plaster ceiling? If this is not what you mean, I don't know what you do mean! But anyway - walls of 'acoustic foam' are not good, you are leaving your bass frequencies to bounce around and muddy everything up. Build some bass traps to start with.
 
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If you are talking about a resonant cavity, fill it with insulation.

Acoustic foam is pretty worthless in a room that size.
 
I didn't say Airbag, I said air "bag", but I get what you mean. My bad, but I do mean what you just said. It's a cavity between the plaster ceiling and the concrete ceiling. Removing the plaster ceiling isn't an option, it wasn't there to begin with. It was the owner's idea so I have to work with what I have.

There's pretty much an entire wall uncovered and I'm planning on hanging a few bass traps there, but what do you think of my idea of putting these bass traps on the plaster ceiling as well? Do you think it might work?
 
That's exactly what I'm talking about, and I did think about filling the cavity with something but I'm not sure that's very practical. I'm not sure it will resist , after all it's a big cavity. You'll see once I get to post the picture.

Either way, if I was to fill this with something, what could I use exactly? And what are my other options?
 
I am still not clear as to what you are talking about 'filling'? Maybe I am just not understanding...The picture did not help really.

If the cavity above the ceiling is creating an issue (which likely it is), then you need to address the problem. If you are serious about this, tear the ceiling down and fix it.

I will make a personal judgment and say that you have not addressed the main problem in your room yet. There is a place for foam products, but only after you make the room useable with proper bass traps.

Trust man. You need to address the low end first. Same story, different space...

Much to find here and other places to get you going in the right direction. Every space is different, but the same basic principles apply to each.
 
jimmys69 said:
I am still not clear as to what you are talking about 'filling'? Maybe I am just not understanding...The picture did not help really.

If the cavity above the ceiling is creating an issue (which likely it is), then you need to address the problem. If you are serious about this, tear the ceiling down and fix it.

I will make a personal judgment and say that you have not addressed the main problem in your room yet. There is a place for foam products, but only after you make the room useable with proper bass traps.

Trust man. You need to address the low end first. Same story, different space...

Much to find here and other places to get you going in the right direction. Every space is different, but the same basic principles apply to each.
Click to expand...

What I mean is that the cavity is full of air, meaning that besides the wires and bars that hold the plaster ceiling in place, there's nothing., just air... Maybe I'm just being redundant. I'm sorry, my bad.

Now, regarding the option of removing the plaster ceiling, that was my first call! But the owner of the place had someone put that plaster ceiling there way before the place even started to look like a studio. His plans involved having a nice looking ceiling in the studio; not very functional though. So my hands are tied and I've been studying other options but I've come to realize that my options are either removing the ceiling (which will hardly happen), or filling the cavity with some material in hopes it'll stop the reverberations. Now, as I stated above I'm not sure what material could I use that's light enough fill such a big space and not tear the ceiling down.

That's why the idea of hanging bass traps from the ceiling came up; but what do you think of this idea? Our theory was that these traps would block the sound from transferring to the ceiling and the cavity, but based on all I've read from you guys I'm starting to think that well, the cavity will always be there and the sound will find a way to get there anyway. What do you think ?

On a different matter, you're completely right about preparing the place with bass traps and then filling "gaps" with acoustic foam. The went ahead and covered the whole place with acoustic foam but I'm going to propose a redesign of the place based on what you said. I was think about putting three big panels on the empty wall with the blue squares you see in the pictures, and then putting angled panels on pretty much every corner between the wall and the plaster ceiling. Oh and also I thought putting three big panels hanging from the ceiling, regardless of what they decide to do with the cavity. Any advice?

Thanks a lot!
 
I've never found the cavity to produce a noise - we really don't have a clue what the problem sounds like - can you record it? I've no idea what sound to expect - bag, bathroom etc - I genuinely have no idea what kind of noise or sound you are hearing? I can understand 'hollow', or resonances, or vibrations but cavities in general help rather than hinder unless they resonate at a particular frequency?
 
rob aylestone said:
I've never found the cavity to produce a noise - we really don't have a clue what the problem sounds like - can you record it? I've no idea what sound to expect - bag, bathroom etc - I genuinely have no idea what kind of noise or sound you are hearing? I can understand 'hollow', or resonances, or vibrations but cavities in general help rather than hinder unless they resonate at a particular frequency?
Click to expand...

That's a great idea. I'll try and record the sound for you.

The sound I'm talking about is like some vibrating, or reverberating. Like, I clap and I hear the sound back from the cavity but very alienated. Even metallic, I'd dare to say.
 
rob aylestone said:
I've never found the cavity to produce a noise - we really don't have a clue what the problem sounds like - can you record it? I've no idea what sound to expect - bag, bathroom etc - I genuinely have no idea what kind of noise or sound you are hearing? I can understand 'hollow', or resonances, or vibrations but cavities in general help rather than hinder unless they resonate at a particular frequency?
Click to expand...

That's a great idea. I'll try and record the sound for you.

The sound I'm talking about is like some vibrating, or reverberating. Like, I clap and I hear the sound back from the cavity but very alienated. Even metallic, I'd dare to say
 
If the ceiling was put in to the building code, there has to be a whole framework of studs in place, and it would have to be able to support some insulation in there, as well (again, per code). Is there any access to the space from outside the room, or maybe a 'hatch' inside the room?
 
mjbphotos said:
If the ceiling was put in to the building code, there has to be a whole framework of studs in place, and it would have to be able to support some insulation in there, as well (again, per code). Is there any access to the space from outside the room, or maybe a 'hatch' inside the room?
Click to expand...

Unfortunately I don't think the plaster ceiling was built to support anything other than its own weight. Where we live it's really warm all year long so insulation isn't a common thing; so I doubt they followed any specific construction code. And regarding the hatch, no there's no hatch but if we were to actually fill the cavity I'm sure we'd find a way to access it. Problem is the owner is reluctant to do it, he wants to stick to the bass traps... on the ceiling only -.-
 
Rodolfo90 said:
... About 60-70% of the wall area is covered in acoustic foam. The real problem here isn't whether or not the foam is working; as the title says there's a sort of air bag (cavity between the ceiling and the plaster ceiling) which creates a sort a rattling noise whenever we make a loud sound such as clapping or even the snap of fingers (around the center of the room). ..
Click to expand...

You guys is silly. :facepalm: Snappin your fingers ain't 'rattling some space above the plaster.
This is flutter echo. With all the foam, ceiling to floor likely the worst of it

Clue two-
PD: The rattling sound I'm talking about sounds more or less like the "Bathroom" filter you find in many recording software.
Click to expand...
Small room flutter and 'box resonance
 
mixsit said:
You guys is silly. :facepalm: Snappin your fingers ain't 'rattling some space above the plaster.
This is flutter echo. With all the foam, ceiling to floor likely the worst of it

Clue two-

Small room flutter and 'box resonance
Click to expand...

Ok, now you're talking. Flutter echo, got it. What do I do about it then ? Have you checked the pictures of the place and the recording of the "echo" ? I'd appreciate any help you could give me.

Although, I remember hearing that sound even before the cover the walls with foam. What do you think?
 
mixsit said:
Plug in 3.4, 1.8, 2.6 here. (guessing 8.5 foot ceiling

Click on 178 cycles. That's well with in the vocal range, and below where your 3/4" foam diamonds' mounted w/o an air gap drop off.
(Mounting off' the wall extends their range some
Try some 2-3" clouds hung from the ceiling as well?


(BTW- "3/4" was a guess. But going by average depth. (The 'peaks don't get full credit :D
Click to expand...

All right, I don't think I'm following, I'm sorry. Let me see if I get this right:
When you talk about the clouds you mean hanging absorbing material there right? it's more or less the same as mounting some bass traps right ?

And also, the calculator link you sent... am I supposed to cover with panels the darker areas? I read the darker are are the areas with the highest pressure therefor the loudest. I'm not sure if that means I'm supposed to put panels there.

Thank you very much for taking the time to do this! :thumbs up:

Btw, the order link you sent about absorption coefficient looks great.
 
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