Air gap in exterior windows

Regarding the physics of desirability of air space between glass panes: I'm constructing a new project studio with 2x6 exterior walls that will house some version of dual laminate/plate glass panes. Is there any reason not to incorporate as much air space allowed by the dimension of the walls? Sorry if this has been discussed prior ... can't seem to find info on this. Common sense would seem to dictate that more space is better.... tia greg hilfman

Hi Greg. Welcome! Please read the forum rules for posting (click here). You seem to be missing a couple of things! :)

Is there any reason not to incorporate as much air space allowed by the dimension of the walls?

As much space as you possibly can is what you need, and even more than the average depth of the air gap between the drywall leaves, if possible. Your wall is a tuned "MSM" system, where MSM means "Mass-Spring-Mass". Same principle of physics as a weight bouncing up and down on a spring, governed by well-known equations. The concept is that the wall does NOT isolate at the frequency it is tuned to, but isolates BETTER than mass law at frequencies above about twice the resonant frequency. So if you tune the wall to a low enough frequency, it will isolate the entire audible spectrum, or at least the part you are interested in. How do you tune it? There are only three factors in the simplified form of the equation: the amount of mass on each side of the air cavity, the depth of the air cavity, and weather or not you have "damping" in the cavity. Damping just means something that acts against the resonance, like a shock absorber in a car's suspension (which is also a tuned MSM system). For acoustics, a good "shock absorber" is fibrous insulation, such as mineral wool or plain old "pink fluffy" fiberglass. So, if you need more isolation you can do one of three things: Increase the mass on the leaves, increase the air gap between them, or fill more of the air gap with insulation. All of those will lower the resonant frequency, which is what you want. So think about it: You will have insulation between the two sides wherever you have drywall, but of course you cannot put insulation between the panes of glass! You want to see through there, so you can't have insulation. So you have taken OUT one of the factors that you need in that area. You therefore either have to increase the mass (make the glass a bit heavier per square meter than the drywall is) or increase the gap (have a greater distance between the two pieces of glass than there is between the two leaves of drywall. Or do both: more air space and also more mass. Simple! :) So, whatever frequency you tuned the rest of your wall to, you need to tune the window section to the same frequency, or lower. So anyway, in theory you need 1.4 times the air gap to compensate for the lack of insulation (don't ask why...) Or you need more mass (thicker glass), but the amount of extra mass depends on other factors.... It gets to be complex.

some version of dual laminate/plate glass panes.

Laminate glass is the best, but other glass will work too, if it is thick enough. - Stuart -