Are Windows of same thickness THAT problematic?

[leski]

Hi all
About to commence construction on my new Irish studio and have been looking for tempered glass...anyhow..found 3 panes 20mm (3/4") thick and about 1.5 x 700 m which i thought were perfect..
However, I am aware that people seem to advise against putting windows of the same thickness opposite each other (control room window)..Is this because they would share the same resonant frequency and encourage standing waves?
How much of a problem in real life would this be?

Thanks,

Les

[Soundman2020]

It's not really about the internal MSM resonance of the cavity between the two panes of glass, but rather is about the resonant characteristics of the glass itself, ans especially one specific type of resonance, know as "coincidence": It's complicated to explain (bending waves, and the speed of sound in different materials, and fun things like that), but basically all panels have a "coincidence" frequency, and at there's a large dip in the transmission loss for the panel at that frequency. Not surprisingly, that is called the "coincidence dip", and if both panes of glass are the same thickness, then the dip occurs at the same frequency for both sides, so tones around that frequency will not be isolated as well as other tones.

That said, with 20mm glass on each side and a good air gap, you are going to be getting pretty darn good isolation anyway, so the coincidence dip is not going to be a huge problem. I wouldn't be too worried about it, unless you are looking for very high levels of isolation. With that configuration well mounted and sealed, your windows will probably be isolating better than your walls!

- Stuart -