Soundproofing windows

[Chill]

Time to soundproof the windows in my basement. They are 17" H x 34" W, single pane, wood frame, with a thin sheet of plastic about 2" away on the exterior to make them translucent. Seems like they are a weak link compared to the stud wall and concrete right next to them.

How would you go about soundproofing windows? And any experience/ thoughts/ insight on these methods, assuming proper sealing and airtightness:

Wood plugs, essentially a solid core door for the window. Advantage: cheap, easy to build up layers for thickness/ mass. Disadvantage: no more natural light (which can be cured with a hinge).

Sheet of acrylic mounted on an extra frame on the interior. Advantage: passes light, about 2x as dense as wood, can be built up from small layers. Disadvantage: cost, especially as the thickness of the sheet increases.

Additional glass mounted in an extra frame on the interior. Advantage: passes light, about 4x as dense as wood. Disadvantage: possible breakage, costly after 1/2" thickness.

Dual pane vacuum sealed glass (1/4" on either side) mounted in an extra frame on the interior. Advantage: passes light, 2 layers of thinner/ cheaper glass, air gap should help reduce conduction. Disadvantage: possible breakage. Believe it or not, a local glass house quoted me less for the sealed dual pane with 1/4" each side than for the single pane of 1/2", and it was about half of the cost of similar 1/2" acrylic.

[Chill]

The Canadians have an interesting study on window sound transmission:

http://irc.nrc-cnrc.gc.ca/cbd/cbd240e.html

Figure 2 suggests that sealed double pane 1/4" (6mm) windows with the panes spaced 3" (75mm) apart is about as efficient as you'll get, at STC 45. Plexiglass behaves about the same way as regular glass of the same mass. So...

(4) Single pane of plastic mounted on the exterior and caulked for airtightness. By happenstance it'll be about 3" away from the interior glass pane.

[mshilarious]

Originally Posted by Chill

The Canadians have an interesting study on window sound transmission:

http://irc.nrc-cnrc.gc.ca/cbd/cbd240e.html

Wow there's a real bombshell there:

Although non-parallel mounting of the glass is a well established practice for windows in recording studios, no acoustical benefits of this practice are discernible in careful laboratory measurements. The TL of windows with slanted glass is essentially identical to that for parallel glazing with the same average interpane space. Parallel glazing at the maximum spacing permitted by the supporting wall gives optimum noise reduction.

[iced]

you could build one BIG acoustic panel .. and stick it in the sindow thats what i did .. and it works ok. for now

[gullfo]

yeah that is strange... i thought the angling of the glass was to reduce the possibility of resonant freq modes due to the parallel surfaces... much like you would design a studio and control room to avoid parallel surfaces to direct the reflections and avoid resonant freq modes...

[iced]

Window******

[mshilarious]

How is the STC of a system of two windows calculated? Let's say I have a double glazed window with a STC of 31, and I add a storm window with STC of 24. The storm window is 3" from the window, which I know makes a difference--is there some distance at which the STC are simply summed, and closer than that, there is a formula to figure the net STC?

Not trying to get too fancy an answer, I just wanna see how I could get window STC close to the walls.

[Chill]

Originally Posted by mshilarious

How is the STC of a system of two windows calculated?

Empirically!

Let's say I have a double glazed window with a STC of 31, and I add a storm window with STC of 24. The storm window is 3" from the window, which I know makes a difference--is there some distance at which the STC are simply summed, and closer than that, there is a formula to figure the net STC?

The double paned glass doesn't do much in that configuration, it acts more like a single pane of glass with the total mass of both panes. That was in one of Quirt's papers on the NRC site, it may be the one above or his 1981 paper.

I saw some numbers for increasing the distance between the panes and it seems like things leveled off in the 40's, even for windows a foot or two apart.

[iced]

im confuseld