Double leaf: can I put all rockwool on one side?

[jaapgvk]

Hello,

I was wondering if, acoustically speaking, it matters where you put your rockwool/fibreglass on the inside of a double leaf structure.

This is what I want to do in my situation.

Screenshot 2016-10-04 at 19.08.22.png

Red = brick wall (10cm)
Yellow = rockwool (30cm)
Grey = plasterboard (2,5cm)

It's easier for me to put all the rockwool on one side. But does it matter? Or is it better to divide the rockwool equally between the two sides?

I can't find anything in the 'IR papers'. Could someone shed some light on this?

Also: would it matter if the rockwool would be in the middle (that is, not touching either wall)? Because it maybe easier to just 'drape' the rockwool over the outside of the wooden structure, thus leaving about 5cm of air between the rockwool and the inner leaf.

[Soundman2020]

You get maximum isolation when the entire cavity is filled with insulation, not just part of it.


- Stuart -

[jaapgvk]

Thanks for your reply Stuart. Greatly appreciated.

I am aware that, theoretically speaking, you get the best isolation when you fill the entire cavity. Although this graph from ir-811 would suggest that, using glassfiber, anything above 80% is redundant.

7f863334-a856-453f-95f9-4b6f8fa91a34.jpg

In my example, I'd be filling up 75% of the cavity (30cm of the 40cm). This is partly because of budget, and partly because in my specific case it would be easier to install.

Or do you think that reducing the space between the leafs to 30cm is better, isolation-wise, if I'm going to use 30cm between the leafs? I chose 40cm because I wanted to keep the resonant frequency as low as possible (below 30hz). (The leafs are 25mm plasterboard btw.)

So, to come back to my original question: just theoretically speaking, does it matter where in de cavity I place my fibreglass? Is it just a simple adding up of isolation and cavity width, or does it have to be placed right against either side of the leaf? Or could it also just 'hang in the middle' so to speak?

[Soundman2020]

Although this graph from ir-811 would suggest that, using glassfiber, anything above 80% is redundant.

The graph doesn't say what you think it says! You asked a question about insulation inside walls for MSM resonant systems isolating air-borne sound with a brick wall as one leaf. What that graph shows is the effect of insulation on sound structure-borne impact sound transmission through timber-framed floors. Very different thing.

Interestingly enough, that graph clearly shows that mineral wool is superior in all cases for dealing with impact noise in wooden floors...

Or do you think that reducing the space between the leafs to 30cm is better, isolation-wise,

Definitely not! Keeping the air gap as large as possible, and the MSM resonant frequency as low as possible, is paramount.

However, having said that, it's VERY unusual to find a situation where you need a 40 cm air gap! That's huge. What do you need to isolate that requires such a large air gap? I mean, there's nothing wrong with that, if you can spare the space, and it will indeed provide good benefits, but most home studio builders simply cannot afford to lose so much floor area. Room volume and floor area are also very important, for studio acoustics. If having such a large cavity means that the room volume is compromised, then you should look at other methods for getting the isolation you need.

I chose 40cm because I wanted to keep the resonant frequency as low as possible (below 30hz).

My calculations show your MSM resonance would be about 16 Hz with the situation shown in your diagram, and your overall isolation is pretty much already limited by flanking through the concrete slab. I don't see a need to have such a large air gap. Overkill.

So, to come back to my original question: just theoretically speaking, does it matter where in de cavity I place my fibreglass? Is it just a simple adding up of isolation and cavity width, or does it have to be placed right against either side of the leaf?

In your case, I would put it up against the drywall (plasterboard). There is some evidence (from the Wyle Report, IIRC) that insulation can provide some mechanical damping to the panel itself, which is slightly beneficial. The difference isn't huge, but worthwhile if you are looking for very high isolation.

- Stuart -

[jaapgvk]

Thanks again for your informative reply

I see that the IR-811 graph is not what I wanted it to be It's just. I'm seeing a lot of numbers flying by and sometimes it's hard to keep up with what I'm reading. I'm by no means an expert.

The primary function of the studio is to be able to practice day or night (recording is not important), so isolation is more important than acoustics. The most important instrument that will be played is a drumkit. I'm trying to get as much reduction in the 'below 100hz' range as possible (I've calculated 60hz for the kickdrum). That's why I chose for the 40 cm space between leafs: to get the resonant frequency as low as possible, so the drumkick won't leak through the walls (people are sleeping in an other house, some 20 meters away). I don't have an exact number 'db-wise', but if 50db in the sub 100hz could be possible, that would be great.
Having said that, every extra cm of studio area I can get would be awesome, because we're with four persons.

But if I could go half of the 40 cm, that would be awesome, and also: then it wouldn't be a problem budget-wise fill the entire cavity with fibreglass (or rockwool).

Is there a calculator that I can use to calculate the resonant frequency? Because if I could go for way 20 cm's and get away with it, that would be golden!

And indeed, there is a concrete slab, so there will be flanking. If the spacing between the walls doesn't way up to that, there isn't much sense in having a 40cm gap.

Oh, and what I meant with 'reducing the 40cm to 30cm' is that that would make sure that the entire cavity would be filled with rockwool (because I calculated 30cm of rockwool).

I'm gonna try and get the Wyle Report. You can never have enough knowledge

[khrisna]

dear

have u calculated the stc ratio from this isolation inside the booth ,similarly im think to do that

normally my brick wall room gets stc ration around 40- peak 75 db in day..

i want to sound proof it..

[jaapgvk]

I'm sorry khrisna, could you try and rephrase your question. I'm afraid I don't understand

[jaapgvk]

Allright. I've done some calculating.

The images with the brick are the walls.
The images with the plasterboard on two sides are the roof.

plaster_plaster300_300.jpg

plaster_plaster400_300.jpg

plaster_plaster400_400.jpg

wall_plasterboard300_300.jpg

wall_plasterboard400_300.jpg

wall_plasterboard400_400.jpg

Like I said. I wanted to keep the minimum resonant frequency below 30hz.

You were right about the resonant frequency of the walls. It would probably be very low. About 20hz says the program. But I neglected to say that the roof is made of different material, comparable with two sheets of plasterboard. So there would be a different resonant frequency going on there.
Should the spacing/rockwool of the wall and roof be adjusted, so that they become comparible in resonant frequency, or is it the 'weighed avarage' which will define the eventual resonant frequency? i don't know enough about sound to be able to say anything about this.

The walls and the roof share the same space between the leafs (it's a tilted roof). That means: it's one big space.

twee delen.jpg

So, according to my calculations. It would be no problem to keep the distance between the wall and inner leaf 30cm and the distance between the roof and inner leaf 40cm.

I don't really know what my actual question is anymore
I just... I just want to make sure that what I'm doing is 'kinda' correct.

[khrisna]

Dear
I'm know little about insulation
But you can see single leaf means in your condition- brick wall (big mass) then ,then fix insulation rock wool against the wall by using stud on the wall, with studs ,then cover with the gypwall board over insulation , this is single leaf I think ,leaving gap ( your idea) doesn't make difference in sound attenuation .

If u want double leaf means room in a room method ..

[Soundman2020]

brick wall (big mass) then ,then fix insulation rock wool against the wall by using stud on the wall, with studs ,then cover with the gypwall board over insulation , this is single leaf

No. That is a coupled 2-leaf system. There is still MSM resonance in a system like that, plus the lost isolation due to the direct flanking though the studs. Very poor isolation.

I think ,leaving gap ( your idea) doesn't make difference in sound attenuation

Of course it does! The air gap acts as a spring! It is part of the Mass-Spring-Mass resonant system that is created by having massive leaves on either side. Air is a very good spring, as far as sound waves are concerned. The larger the air gap, the lower the resilience.

If u want double leaf means room in a room method ..

No. A double-leaf system is ANY time you have two leaves with substantial mass and an air gap between them. There will ALWAYS be resonance going on in such a system, and the resonance is described by this equation:

MSM-resonance-equation.jpg

If you have a 2-leaf system, and you add a third leaf to it, as you suggest, then it's a different equation:

3-leaf-MSM-resonance-equation.jpg

As you can see, the resonant frequency in such a system will always be higher than for the equivalent 2-leaf system, and therefore the isolation will always be worse in the low frequency end of the spectrum. 2-leaf is always better than three leaf, all other factors being equal.


- Stuart -

[Soundman2020]

Allright. I've done some calculating.

Ummmm....

STC-98-funny.jpg

STC 98???


Nope. Just nope. That won't happen.

I'm not sure what software that is, nor what parameters you entered into it, but you will NOT be getting STC-98 from any reasonable combination of those building materials. It is physically impossible.

The very best isolated studio on this planet is Galaxy Studios, in Belgium. They get just a fraction over 100 decibels of isolation. They spent many millions of dollars to do it, and in order to get that type of very, very extreme isolation this is what they had to do:

galaxy-studio-best-in-world-SPRINGS-PHOTO-2.png

What you are looking at there, is the underside of the studio floor. The studio itself is a massive concrete bunker, with concrete many,many inches thick, and it is isolated on those springs and pads, inside another concrete bunker. It is a true "room in a room" 2-leaf system, where the inner room is fully floated on those springs, inside the outer room. That system was designed by some of the best acoustical minds in the world, one of whom used to be a member of this forum, until he passed away a few months ago.

That is how you get 100 dB of isolation. Not with drywall and mineral wool.

So your simulation is grossly invalid. There simply is no way that you will ever get 98 from a few sheets of drywall. I suspect that either the software you are using is badly flawed, or you are using it incorrectly, with incorrect assumptions.

If you want to know how REAL walls isolate, when really tested in real life, in real acoustic studios, then this is the very best document that is currently available to tell you that:

http://archive.nrc-cnrc.gc.ca/obj/irc/d ... /ir761.pdf

Over 300 different walls were tested, and all the results are there. The very. very best wall they could produce came out at STC-69 (see page 350). Most of the walls were in the range 40-50. A very few made it over 60.

So if the very best wall actually test in a laboratory gives about 69, there is no way at all that your wall will be one thousand times better (30 dB = 1000 times greater isolation).

Nope.

Sorry.


- Stuart -

[Soundman2020]

normally my brick wall room gets stc ration around 40- peak 75 db in day.

I think you are using your terms incorrectly. STC is not a ratio: it is a rating system. And getting 75 db of isolation is very, very hard to do. Do you mean that you are measuring the sound level inside the room, using a hand-held sound level meter, and you are seeing a reading of 75 dB on the meter, even when you are not making any sound in side the room? Is that it?

- Stuart -

[jaapgvk]

STC 98???

Hahaha! Yeah, STC-98 is kinda silly. The program is called insul: http://www.insul.co.nz/
I wasn't even considering I would get that kinda sound reduction.

I'm not sure what I did wrong, of if I did anything wrong. The program just gave me these numbers.

And I'm aware of mythical status of the Galaxy Studios and the work of Eric Desart. I would never even imagine to come close to the statistics of that studio. I just want the neighbors to be able to sleep while we're making music.

Oh, and thanks for the formula! I will look into it.

But maybe you have a clue about the question I asked: if the outer leaf consists of different materials (in my case a wall made from brick and a roof made from plasterboard (thus: have different masses)), and the 'spring' is a shared cavity. How is it possible to then calculate the sound isolation?
The walls have a greater density than the roof has. Could I get away with leaving a 30 cm space between the walls and have a bigger cavity (40cm) for the roof to compensate for the fact that the roof has less mass?

Because with doors it's the following reasoning: there is no rockwool/fibreglass between the leafs where there are doors, so the mass of the doors and the spacing in between the doors should be more than between the walls to compensate.
Is the following reasoning rational (considering the walls and roof share the same 'spring'): when I widen the cavity of the 'spring' where there is a roof, this compensates (a little) for the fact that the roof has less mass.

I just. My mind has so much information-crunching to do while planning to build this studio. Maybe I should just integrate all I've learned and then build it on intuition and hope for the best.

[khrisna]

bro....higher stc ratio difficult to get. in programs physics law are should be inculded accurately.

but can get.. but im not expert

you can see the lowest frequency of the table (audible range) ,has more energy and it can travel kms..

you cannot stop a big bom blast sound entering our studio..

try to get 60-65 db isolation for a medium budjet studio

[Soundman2020]

try to get 60-65 db isolation for a medium budjet studio

If you mean "medium budget" in six digits, then 65 is probably achievable. If you mean "medium budget" in four or rive digits, which is a typical for a home studio, that's not going to happen.


- Stuart -