airspace to outside wall

[jrp]

I am sure the answer is here several times, but i can´t find it right now.
We will be constructing a room with 30cm soundproofing walls/ceiling inside our house. How much space should there be between the new wall and the existing 40cm red brick wall?
thanks

[DanDan]

Those are both very thick walls. Did you write the numbers correctly?
The bigger the gap the more isolation you will achieve.
It is best to completely fill the void with light insulation, not compressed. This is to prevent resonance in the void which would couple the two walls a little.
You need to consult a builder or engineer regarding damp/vapour issues.
Most people build much thinner stud and plasterboard walls for the inner.
Here's a full overview of the options and performance. http://johnlsayers.com/Recmanual/Pages/STC%20Chart.htm

DD

[jrp]

the figures are correct.
i made a little drawing showing the walls from above.
Brown is the brick wall of the house. 40 cm
Red is a 12.5mm gypsum 20cm in front of the wall. It is already existing and we plan to leave it because we are not sure what is behind... I could see through a small hole that there is no insulation and that the brick wall is black. Maybe a fire some time ago. House is 100 years old...

Then we have two layers of 12.5 gypsum on each side of the new wall (blue).
Double stud construction, 16cm mineral wool inside.

Now the question is how close can we build our new wall to the existing wall (brick+gypsum).

[Dange]

You need to define a target for your sound insulation. I.e. what is going to be the level inside and what do you want it to be reduced to outside?

The proposed construction contains a triple leaf:



This may not be the best solution.....the triple leaf can be worse at low frequency than a double leaf without careful design.

[DanDan]

The bigger the gap the better.
I am inclined to lose the existing plaster wall. Who knows what will happen with damp unless you go with tried and tested methods.
DD

[Dange]

I'd use the materials in the way I've attached

[avare]

Originally Posted by Dange

I'd use the materials in the way I've attached

Agreed.

Andre

[jrp]

Thanks!
The problem with your suggestion is this:
The recording room we are building is naighbored by the construction shown on two sides.
On on side there will be a 50cm passage between our room and the wall (because there are windows that need to stay acessable)
On one side there is open room.
We will not only build walls but also a roof that has the same construction as the walls.
the drawing shows everything from above.

Our aim is to record and practice music without annoying the naighbors too much.

[jrp]

Also, would it be an option to make some holes in the existing gypsum rather than ripping it all out?

[jrp]

so, it is best to get rid of the existing wall first?
If i leave it and place my new double wall 5cm from the existing wall, what could happen in a worst case scenario?

[takman]

about filling the gap.

it was my understanding that its better to not fill the gap. That ideally we want Mass-Air-Mass. Where the air acts as a spring/dampener.

Its was also my understanding that the larger the gap the better. And the larger it is, the lower the frequency it will start to resonate.

gapped filled or not filled? anyone care to comment?

[DanDan]

The bigger the gap the more the Transmission Loss.
The air in the void can resonate. This couples the walls a little.
To prevent that, fill the gap with light insulation.
This prevents resonance and can add 9dB or so the the performance of the system.
Fill fully, prevent sagging over time using mesh or whatever. Lightly touching each side, particularly the plasterboard on is ideal. This damps any vibes building up. Do no compress it in there, as this would couple the walls at LF.
DD

[takman]

DanDan, maybe im mis-understanding you.

maybe this should clarify.



The air gap in the STC wall is not filled with insulation, rather the spaces between the studs are.

Are you saying the STC63 wall could add 9 DB's of isolation by filling the air cavity?

[DanDan]

I had a link to Gypsum UK research, unfortunately it is no longer active.
Actual tests. Full fill is best. The 9 ish dB improvement is fill vs no fill.
Partial fills such as in your diagram would I presume yield partial improvements. However, to emphasise, everything I have read on this recommends full fill, not compressed etc. as described.

DD

[jrp]

yes, this is exactly what we are building. the rightmost diagram filled with mineralwool.
I just noticed that the wall in the room we are building this in has a thin plasterboard wall standing 20cm in front of the brickwall.
should i rip it out?
i rather wouldn´t...
if i keep it, can i go as close as 5cm with my new wall?
everyone sais the bigger the gap the better. but what is reasonable? 15cm? 30cm?

the brick wall is massive, 40cm red bricks. floor is also massive, 40cm concrete.

[jrp]

in other words, it is the figure to the right with an aditional airspace/layer.
The problem is technically, if i get this right, that the plasterboard wall will go into resonance with the air behind at a certain frequency, right?
THe wall is rather big. 10*2,65Meters on one side, 5*2,65 meters on the other side. Maybe it will resonate below 20hz anyway?
Another idea is to place our new wall directly to the existing wall and cut around our live room so that the part of the wall connected will be seperated from the rest of the wall/building. uh, hard to describe, i hopeyou can get what i mean...
If the cut is around 10cm wide (covered with light cloth), how would that be?

[avare]

From what you are describing, you are proposing the STC 50 wall construction. More material and less isolation than the STC 63 wall. Post drawings accuratley depicting what you are proposing.

The additional leaf will INCREASE the transmission of LF sounds.

Andre

[jrp]

i´m not sure if i understand, we are building the STC63 construction, just with complete filling. Then there is this aditional wall completly seperated from what we are building. Behind it is the Outside wall of the house.
Do you mean that this will behave like the STC50 construction?
Why?

[avare]

Originally Posted by jrp

i´m not sure if i understand, we are building the STC63 construction, just with complete filling. Then there is this aditional wall completly seperated from what we are building. Behind it is the Outside wall of the house.
Do you mean that this will behave like the STC50 construction?
Why?

Words are terrible for communication in engineering. Please post a drawing (with dimensions) of what you are proposing.

Andre

[jrp]

So true.
Sorry, i am terrible with drawing on the computer, all i have is open office...
no scanner also.
I did my best but it´s not much better than what i had so faar...
THis is what we are planning right now.
Orange and brown are existing (brick air gypsum).
Yellow is what we are bulding. STC63 construction.

[jrp]

here it is

[avare]

Originally Posted by jrp

here it is

Thank you. The middle (beige) leaf will make the TL worse.

Andre

[jrp]

how much? Is it a big loss?
i came across this formula, i am not sure if it applies here,
F(R)=60/SQR(10*0.22)
10 being an estemated 10kg/sqm of the beige wall
0.22 being the airgap behind it.
That gives me a resonance at about 40hz for the wall.
Is that correct?

[DanDan]

Another view of it.

STC Chart

DD

[avare]

Originally Posted by jrp

how much? Is it a big loss?
i came across this formula, i am not sure if it applies here,
F(R)=60/SQR(10*0.22)
10 being an estemated 10kg/sqm of the beige wall
0.22 being the airgap behind it.
That gives me a resonance at about 40hz for the wall.
Is that correct?

No. We are talking abiut a triple leaf. The calculation involves the roots of a qudratic equation. Your can find ALL the calculations necesary for TL modeling in Sharpe WL 73-5R.

You have been very persisten in this triple leaf issue. Please post the calculated TL curve so that everyone can see what the effect is.

Andre

[jrp]

thank you! I appriciate your help.
right now i feel a little lost with this information, also my english is quite rudimentary when it comes to technical terms and papers.
Anyhow, the reason why i have been persistent is that i am somewhat afraid of whatever is behind this wall. Might be a hidden gold treasure, might be a pile of dead rats... propably the later. This place is 100years old and has had many uses and owners... Whoever put up this wall must have had a reason.
I guess you experiance this every day, people not listening to good advice. I do not want to make this mistake.
Still looking at this document, apperently it is not easy to say how big the effect will be.
tomorrow i´ll pick up a dictionary and go through the table of contents, see if i can find the right formula.
btw, those 10kg/sqm are just a guess for this wall, it might be less since it feels really thin when knocking against it.

[avare]

Originally Posted by jrp

.
Still looking at this document, apperently it is not easy to say how big the effect will be.
tomorrow i´ll pick up a dictionary and go through the table of contents, see if i can find the right formula.
btw, those 10kg/sqm are just a guess for this wall, it might be less since it feels really thin when knocking against it.

The equations on triple leaf are detailed stating on pdf page 47. 10 kg/m² seeems incredibly light.

Good luck!

Andre