Control room window construction

Hi guys, I am nearing the end of studio construction and am getting ready to complete the window from control room to live room. I just need some clarification on whether the whole window is hermetically sealed or not? How important is this? In this diagram it shows fiberboard closing the gap in the two separate stud walls. Does this not defeat the purpose of having the two walls separated as its creating a bridge between the two walls? At the moment I have the frame in with only insulation and fabric covering the cavity void between the two walls, just wanted to get some clarification before installing the glass. Does it make a big difference if its not sealed all round? Oh and as with the debate with whether to angle or not. Well maybe I won't bring that up. Thanks for your help in advance!

I just need some clarification on whether the whole window is hermetically sealed or not?

Yes! Both panes of glass must be fully sealed into their respective leaves.

How important is this?

Critically important! Each leaf must be totally air-tight. Even a tiny gap can transmit a lot of sound. So it is not just your windows that must be sealed, but the actual leaves themselves. Each leaf must create a fully air-tight "shell".

In this diagram it shows fiberboard closing the gap in the two separate stud walls. Does this not defeat the purpose of having the two walls separated as its creating a bridge between the two walls?

Not really, because fiberboard is very soft and does not transmit vibration well at all, and it is also covered with insulation and cloth. The amount of flanking you might get through that is very small. However, even so, it is best to attach the fiberboard on only one side, to just one of the leaves, and leave a small gap at the other end, so it is "floating" without actually touching the other side. If you make the groove in the window frame for the fiberboard inlay a bit smaller than the board itself, then you can just fit it in by pressure alone. Make the groove on the other frame a bit larger, so it does not grip the board at all.

just wanted to get some clarification before installing the glass. Does it make a big difference if its not sealed all round?

Yep. It can cost you many decibels of isolation by not sealing the glass into the leaf. It is fairly easy to do: resilient rubber strips around the edges of the glass, and/or acoustic caulk will do the job. - Stuart -

Hi Stewart thanks for your reply! So I understand that each leaf needs sealed going in but does the space between the two windows need to be sealed also? If so would there be a tight enough seal with only butting up the fiberboard with out having a tight fit on one side? Is the fiber board necessary or would the insulation covered in material be enough that I already have here? Thanks! Fra

No, it isn't necessary to seal up in that sense. There's no real point to it, since the air gap between the windows is basically part of the air gap between the two entire leaves. The soft fiberboard, insulation and cloth provide some degree of separation, and there's no need for more than that. Another important point about the air spaces between the glass: there should be enough desiccant in that gap to ensure that there is never any condensation- I use silica gel, as it is inexpensive and very effective, but there are others too. - Stuart -