How to build stacked windows correctly?

[Didi_n]

Hi everybody,

I built a house in Austria / Europe during the last year and a half and predisposed a part of the basement for a home Studio/ rehearsal room.
You can find a sketch of the rooms in the attachements.

The bigger room will be used as live / rehearsal room, the smaller one as control room with the hearing position facing to the wall in the bottom.

I have a question regarding the windows. When building the concrete walls there was used a special system where a plastic frame is integrated in the concrete wall and the window frame /wing unit is clicked into this support frame later. This is a picture of the system.
http://www.baulinks.de/webplugin/2006/i/0529-mea2.gif
The windows are Austrian standard double layer tempered insulated glass, the noise reduction ratio is listed at -30 to -34dB
Since this is not enough and there are no acoustic windows available for this system I purchased a second set of standard windows to build a stacked construction. The second set is slightly larger in order to make the wing of the outer window fit trough the frame of the inner and so being able to fully open the windows.
Can anyone give me some input for the construction of the framing for the second window regarding sound insulation, distance etc. maybe someone has done a similiar window construction before?

thank you and best regards

Didi

[Didi_n]

Any ideas anyone?

thank you, Didi

[Soundman2020]

and so being able to fully open the windows.

If you need good isolation, they "operable windows" ar a bad idea. Good isolation requires totally air-tight seals around the window, and that is hard to do with windows that open. You should use only windows that are fixed in place, and do not open.

- Stuart -