Quick question. Outside wall, more mass is better... or not?

spitzer

spitzer

New member
Hi

This is one really old debate to me, with an old friend. It's about a garage door and the question is about sound going out.

Which is the better choice: a) one REALLY thick layer (50 cm) of particleboard, or b) at least two layers, separated by an air gap or gaps?

I would even tend to think the isolation wall could be made to be thinner in total for the same reduction by using the air gap variant (not to mention the wall in question is the only way to get air in/out so you need to drill).

But I really simply don't know. Which one blocks the most dB?

EDIT: I guess I typed the "quick" question too quickly. What I'm referring to here is a LARGE door, so in effect it's an isolation WALL anyway. The basic question is still this. Which one: a) ONE thick, REALLY thick, isolation layer or b) two or more thinner layers.
 
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Most pro studio doors are high-density, solid core doors...no air gaps.
There's some use for an air gap...like when building a double wall...but usually those wall already have quite a bit of mass to them.

One thing to think about...sound is easily transmitted through air.

At any rate, for a garage door, to keep sound from going out...I think you will need more than what you expect, assuming you're talking about 100% sound containment, though that may not be really necessary, just substantial reduction.
 
I couldnt get an appropriate door so I just purchased a standard hollow core internal door and stuck a sheet of 50mm reconstituted foam completely over the inside of it and so it fitted tightly around the door opening.
 
And my edit to the OP here, since based on the answers there's much room for misinterpretation: EDIT: I guess I typed the "quick" question too quickly. What I'm referring to here is a LARGE door, so in effect it's an isolation WALL anyway. The basic question is still this. Which one: a) ONE thick, REALLY thick, isolation layer or b) two or more thinner layers.

It would be a door several meters both wide and tall, so not really a "standard" door in any sense. Sorry. Now back to to the matter at hand.
 
Simplified even more: You're building an isolation wall, designed to block sound. There are two approaches. The first one is: you take 10 boards (low density fiberboard) and screw them together to make one massive wall, 50 cm thick. The second one is: you take 4 boards (low density fiberboard), screw 2 of them together, leave a gap (rockwool, whatever, you decide) inbetween and screw the other 2 boards together to make a wall that is a total of 50 cm in depth.

Both types of wall would have two (four) relatively small holes placed for ventilation.

Which wall blocks sound more effectively, and how significant is the difference? 5 dB SPL? 30 dB SPL?

Sorry again and I hope this time I was able to better convey what I meant to convey.
 
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There are some good BBC papers on this very subject mainly written by G.D. Plumb (G.D. Plumb - BBC R&D). It has been a few years since I last read them but I'm fairly sure that the conclusions were that two walls separated by an air gap were more effective than one wall. The main problem with a single wall is that vibrations are easily transmitted from one face to the other whereas, with a double wall, there is a compliant layer of air between the two structures which eliminates this problem. Of course this assumes that the walls are properly constructed with a compliant layer where the wall meets the floor and any other structure.
 
50cm ~ 20" thick. That's a massive amount of particle board! Figuring a single garage door, 6'x8' (just for ease of use), a single 3/4" thick particle board 'door' of this size would weigh 163 lbs. 26 layers of 3/4" particleboard (not quite 50cm) would weigh over 2 tons!
 
particle board? MDF is dense, while chipboard is much less so. I'd include weight when it comes to describing sheet types. A timber frame with sheetrock on both sides acording to some respected books is less effective than two frames with sheet on inside and out, leaving the interiors as a void.
 
mjbphotos said:
50cm ~ 20" thick. That's a massive amount of particle board! Figuring a single garage door, 6'x8' (just for ease of use), a single 3/4" thick particle board 'door' of this size would weigh 163 lbs. 26 layers of 3/4" particleboard (not quite 50cm) would weigh over 2 tons!
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That's correct! No, really, that IS correct, meaning it wasn't a typo or other error. And the garage were talking about in this "assignment" has double doors, so it's even more, like 2 times 8' x 10'.

Absolutely the single largest part of the debate (the one I had outside this forum) was in fact about that exactly. Why on earth would you use such a ridiculous amount of material, it literally weighs TONS, it's impossible to move, difficult to modify it once it's in place, it's even just so BIG that the space it takes up becomes a problem. Why do that... IF you could do a substantially thinner and lighter wall, just using a simple void (air gap) to your advantage?

I know I started this as a "quick question", but to expand just a little bit what I'm going for is: Yes, a super-heavy wall like that will block sound effectively, no doubt but my bold stupid common sense head says you could HALVE it, you could make it a 25 cm wall instead and get the same reduction, just build it with an air gap. I have read so many times that adding more layers to a single wall does not help beyond a certain point that it's literally stuck in my head.

Rob aylestone: I can't specify it beyond "low density fiberboard" right now, as this is more of a thought experiment (I also said the air gap could be rockwool or "whatever, you decide"). But it (the board, not the air gap...) would absolutely be something relatively heavy, and also it would be the same in both scenarios. So you could substitute whichever type of board you like, it would still be one solid 50 cm wall against (basically) two thinner walls spaced 50 cm apart.
 
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Too simplify greatly I seem to recall that two walls with a void will attenuate sound better than a single wall of twice the thickness becuase there is a "mismatch" in the transfer of sound energy from solid to gas-gas to solid. The same reason why sound travels very badly from air to water or V-V.

Dave.
 
ecc83 said:
Too simplify greatly I seem to recall that two walls with a void will attenuate sound better than a single wall of twice the thickness becuase there is a "mismatch" in the transfer of sound energy from solid to gas-gas to solid. The same reason why sound travels very badly from air to water or V-V.

Dave.
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Excellent simplification! If to give a suitably accurate answer means simplifying "greatly", then by all means! Considering the level of abstraction the question itself was at, that answer is proper proper. (Going deeper requires more information than was given...)

Ok, I'll elaborate. Something like this actually exists, although strictly speaking it has an air gap. It exists as it does because it has been built over a long-ish period of time, each time adding more layers. The structure is basically outside ---> regular garage door ---> one inch of air ---> huge thick isolation wall ---> inside. There's also regular size double doors in the wall and two ventilation holes 10 cm in diameter. Also the innermost layers aren't LDF, they're drywall, maybe for some kind of fireproofing purpose (don't know, could be just more mass).
Since it does in fact exist, I've been able to measure that it blocks at least 30 dB -- and more than a double plastered brick wall. Drum set inside, cannot get any spikes over 90 dB outside. Only low frequencies come through.

You might now see where I'm going with this. Isn't it built "backwards"? Could you just leave out some of the layers and get the same reduction in SPL? Or make it outside -- garage door -- inch of air -- isolation wall WITH 15 cm air gap (rockwool) -- inside ? (this last one, yes, fif-TEEN cm, using the argument that it does not NEED to be anywhere near as big as it is now)

Oh, and it's not mine. I've just been saying for a long time that that's not how you build an isolation wall (or so I've read).
 
spitzer said:
Ok, I'll elaborate. Something like this actually exists, although strictly speaking it has an air gap. It exists as it does because it has been built over a long-ish period of time, each time adding more layers. The structure is basically outside ---> regular garage door ---> one inch of air ---> huge thick isolation wall ---> inside. There's also regular size double doors in the wall and two ventilation holes 10 cm in diameter. Also the innermost layers aren't LDF, they're drywall, maybe for some kind of fireproofing purpose (don't know, could be just more mass).
Since it does in fact exist, I've been able to measure that it blocks at least 30 dB -- and more than a double plastered brick wall. Drum set inside, cannot get any spikes over 90 dB outside. Only low frequencies come through.

You might now see where I'm going with this. Isn't it built "backwards"? Could you just leave out some of the layers and get the same reduction in SPL? Or make it outside -- garage door -- inch of air -- isolation wall WITH 15 cm air gap (rockwool) -- inside ? (this last one, yes, fif-TEEN cm, using the argument that it does not NEED to be anywhere near as big as it is now)

Oh, and it's not mine. I've just been saying for a long time that that's not how you build an isolation wall (or so I've read).
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See...same thing in this thread...questions without purpose initially....but then finally you get to the heart of the matter, the reason you are asking. :thumbs up:

It's kinda funny...the way you ask questions in various threads...it's like you're either testing people, to see what they will say...or you are clueless about the topic, but don't want to let on, so you withhold the underlying reasons for the questions so as not to come off like a newb...or whatever.

Dude...it's an audio forum...just talk, say what you think...right or wrong, don' be shy of any debates. It's all just open discussion, nothing that will matter in the long run, because you can still do what you want, and no one really knows who you are...so nothing to lose. :)
 
miroslav said:
See...same thing in this thread...questions without purpose initially....but then finally you get to the heart of the matter, the reason you are asking. :thumbs up:

It's kinda funny...the way you ask questions in various threads...it's like you're either testing people, to see what they will say...or you are clueless about the topic, but don't want to let on, so you withhold the underlying reasons for the questions so as not to come off like a newb...or whatever.

Dude...it's an audio forum...just talk, say what you think...right or wrong, don' be shy of any debates. It's all just open discussion, nothing that will matter in the long run, because you can still do what you want, and no one really knows who you are...so nothing to lose. :)
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I honestly don't know what you mean. Questions without purpose? If I asked you "do you like milk in your coffee?"... would you start thinking what is the purpose of this question instead of answering it?

I really, really don't know what you mean. Just because it's vague at first (to be quick) and I give more details later doesn't mean it doesn't have a purpose!

Are you overanalysing the questions perhaps?
 
spitzer said:
Since it does in fact exist, I've been able to measure that it blocks at least 30 dB -- and more than a double plastered brick wall. Drum set inside, cannot get any spikes over 90 dB outside. Only low frequencies come through.
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After I built my sound room I did a test. I taped up my cordless screwdrivers trigger and ran it outside the sound room. It measured 110db. I then measured inside the sound room by the mic. It measured 40db to 43db.

My sound room isnt armour plated.
It is a free floating 18mm osb built room with 100mm of RW3 rockwool plus 50mm loft insulation and a semi detached 11mm osb interior wall covered in accoustic foam with 100mm bass traps in each corner.
No air gap.
It has a 28mm double glazed window with a drawn across old bath towel kindly donated by the mrs.
A standard interior door covered in 50mm reconstituted foam backed up with a drawn across 15 toggle duvet. Tesco's own of course!

It measures I think 10'x6' x 7' high and was also built over time. Approx 1 month.

I'm quite chuffed at almost 70db's reduction after reading your post. :)
 
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spitzer said:
I honestly don't know what you mean. Questions without purpose? If I asked you "do you like milk in your coffee?"... would you start thinking what is the purpose of this question instead of answering it?
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No...that's different...you're asking me what I like. It's a simple yes/no answer.

What you do is ask something like..."Does anyone know how many people in the world like milk in their coffee?"
Which certainly would make most people think "Why does he want to know that?" :D
 
Orson said:
After I built my sound room I did a test. I taped up my cordless screwdrivers trigger and ran it outside the sound room. It measured 110db. I then measured inside the sound room by the mic. It measured 40db to 43db.

My sound room isnt armour plated.
It is a free floating 18mm osb built room with 100mm of RW3 rockwool plus 50mm loft insulation and a semi detached 11mm osb interior wall covered in accoustic foam with 100mm bass traps in each corner.
No air gap.
It has a 28mm double glazed window with a drawn across old bath towel kindly donated by the mrs.
A standard interior door covered in 50mm reconstituted foam backed up with a drawn across 15 toggle duvet. Tesco's own of course!

It measures I think 10'x6' x 7' high and was also built over time. Approx 1 month.

I'm quite chuffed at almost 70db's reduction after reading your post. :)
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How low does that screwdriver go though? ;) I've done more measuring at my own place, which is a pretty typical garage -- luckily built with brick walls. Up close, an acoustic kick drum will give you over 125 dB SPL in the face and most of that is under 250 Hz. The brick wall does a pretty good job, but still 80-90 dB come through. The higher frequencies... not that much. Around 65 dB or less if there's no bass. Which I guess is what you'd expect, a brick wall probably also weighs a literal ton. What I'd like to do there would be to somehow "map" how the kick drum projects the sound since it's not really consistent or intuitive (putting something heavy directly in front of the drum doesn't help, neither does putting something heavy inside the drum and it's as loud 90 degrees to the right as it is to the back. Being able to literally trap even 5 dB of that sound would be awesome (improving the room acoustics would probably also help, at least on a "placebo" level).

Your room is still pretty hefty! And it shows that properly engineering it really does make a huge difference. If it wasn't free floating, semi-detached... I wonder?
 
spitzer said:
Your room is still pretty hefty! And it shows that properly engineering it really does make a huge difference. If it wasn't free floating, semi-detached... I wonder?
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Yes I think it total it weighed in at over 1000kg. I know this because it is on a wooden floor and I had to work out if it would be strong enough to support the room and two people.

Free floating: .... Acoustic foam strip really works especially if you make it double thickness.:)
 
Orson said:
Yes I think it total it weighed in at over 1000kg. I know this because it is on a wooden floor and I had to work out if it would be strong enough to support the room and two people.

Free floating: .... Acoustic foam strip really works especially if you make it double thickness.:)
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This "floating" thing is actually something I've been wondering about, even if it's was just a single layer wall. Or even a support beam. I can't remember where it was, but in an article or post somewhere someone was building a vocal booth in the corner of a room and the plan seemed to indicate he was planning to "float" the floor by just putting two sheets of rockwool under it. I instantly thought "how is that going to "float"? " The floor itself (plasterboard, mdf, whatever it was) would be big enough to weigh in the tens of kg, any equipment and people standing on it increases that to the hundreds of kg. Wouldn't that just crush the rockwool? ...making it a layer of ROCK and wool packed nice and tight.

I know from experience that even a single, let's say 2x2 meter, 10 mm thick chipboard panel weighs a LOT. I'm sure throwing one old t-shirt under it would be nowhere near enough to make it "float". I wonder how many would... or how much rubber. One fun idea I remember from way back was to make a floating drum riser with I think about 200 tennis balls. No idea who came up with it, but the idea was just to use chipboard or something and drill a bunch of half circles on the underside. I guess tennis balls are cheaper than whatever neoprene sheets actual construction workers would use :D
 
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