Ok new air-gap in the cavity question

[TRANQUILO]

the increased air gap resist's sound transfer in air tight heavy glass filled spaces. Airtight and and with heavy glass fill, or blown in, but able to be air sealed are best. If it is airtight then it is flank less.

[demetrisag]

Originally Posted by TRANQUILO

the increased air gap resist's sound transfer in air tight heavy glass filled spaces. Airtight and and with heavy glass fill, or blown in, but able to be air sealed are best. If it is airtight then it is flank less.

So two fantastic senarios here

1. Let's say I have an air-gap 10inches, and fill 2 inches with insulation on one side and 2 on the other side with pure air 6 inches

2. and I have an air-gap 6 inches, and again fill 2 inches with insulation on one and 2 on other side this time with pure air in between 2 inches.

Which one would be more effective? (talking about two stud wall configuration of course)

Thanks

[gullfo]

Couple of things to consider, if you have 2 back to back 2x4 walls with a 2 inch gap, you have 9 inches of air space. Filling that with R13 on each side will leave a small open air space which will allow the pressure in that space to flow and equalize. This "loose" air space will help much more than dense insulation or a lot of sealed air pockets. If you have the space, use more, if not, recognize that the framing has space "built in" so the actual gap between the frames can be as little as 1 inch and still have plenty of air space. As noted make sure the room air space is sealed from the inter-wall air space for best performance.

[demetrisag]

Originally Posted by gullfo

Couple of things to consider, if you have 2 back to back 2x4 walls with a 2 inch gap, you have 9 inches of air space. Filling that with R13 on each side will leave a small open air space which will allow the pressure in that space to flow and equalize. This "loose" air space will help much more than dense insulation or a lot of sealed air pockets. If you have the space, use more, if not, recognize that the framing has space "built in" so the actual gap between the frames can be as little as 1 inch and still have plenty of air space. As noted make sure the room air space is sealed from the inter-wall air space for best performance.

Great reply gullfo, you've actually made me realise the space in the studs too. even though I somehow knew that before too, now its even more clear.

I'm going to build my walls around the the house columns which are 14 inches, so I was thinking for metal studs 4 inches.

Put one on each side of the column with gap between the studs 4.5 inches (including the space I need for drywall)

Then fill the studs with insulation 4 inches each as well (40kg/m3 rockwool). So I will have 8 inches of insulated air (both sides) and 4.5 inches pure air.

Do you think is there anything I could do better? I mean maybe if put less rockwool would better as an example? anything? Or is it good enough?

Was wondering about my columns, they are solid concrete 14 inches, would they be good enough on their own without soundproofing?

[gullfo]

i would go with lighter insulation in the walls (24kg/m3 or slightly lower). the concrete columns will conduct sound so if they are in your rooms you likely want to isolate them.

[demetrisag]

Originally Posted by gullfo

i would go with lighter insulation in the walls (24kg/m3 or slightly lower). the concrete columns will conduct sound so if they are in your rooms you likely want to isolate them.

What do you mean the will conduct sound?

It would be a real problem though to isolate them cause then my space will be greatly reduced even more. However I should mention I have only one in the recording room and two in the listening room. If its really nesecessary I could isolate at the cost of space only where the columns are. Right now I have 3,3meters width

And so you are saying 24kg rockwool would be better than 40 then?

Here is a picture for more detail!

[gullfo]

ok, so the columns are outside the room in that case, just make sure you clear them and have some space to put a little bit of insulation in between the column and drywall - this is where the lighter weight type will be handy to avoid coupling the wall to the column via the insulation.

[demetrisag]

So you are saying I should move my studs a little bit more forward in order that the drywall then sits not exactly on the columns but leave an air-gap behind it filled with insulation right?

Though that would cost me at least another 1,5 inches of space in an otherwise relatively small witdh room 3,3m.

Would it worth it at the end?

Only asking out of curiosity now. If I leave it as is. will this drop my results (STC let's say) much down?