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I came across an interesting question posted on Slashdot recently...
"I live at the corner of one of the busiest intersections in my city (pop. 350k). Although I've replaced all windows, insulated, and caulked every square inch of the place, the fire trucks and cars with obnoxious stereos still regularly intrude on my home office. Most of the noise comes in through the windows. I'm considering mounting an oblong parabolic reflector in the ceiling above the windows with a steady feed of white or brownian noise directed into it (e.g., via a small speaker placed within the reflector) to create a 'wall' of sound that would act as a buffer to the outside world. Active noise cancellation would be nice, too, but that's probably more than I want to take on. I don't see any products on the market for this sort of thing. Does anyone have any experiences to share with similar homebrew noise remediation efforts?"
Now it would be easy to say that the proposed solution just won't work. But to say that a potentially crazy idea won't work before trying it out would have us all still living like The Flintstones. But my feeling is that it won't work.
With sound insulation, the tried and tested solutions are usually the best. Firstly, if at all possible, get away from the source of the noise.
If that isn't possible, the cheapest and most reliable solution is to block the noise using a massive, solid barrier to reflect it back to where it came from. Since it is the window that the noise is penetrating, the only practical option is to use glass.
Fortunately glass is an excellent material for sound insulation, and I have in the past made an insulating window myself and the results were good. Here's how I did it...
Improving the sound insulation of a window
The existing window was framed in metal with around twelve or so small panes. Dating from the 1920s it wasn't without a few gaps here and there. I sealed the gaps and also sealed three opening panes shut.
The depth of the reveal was around 250 mm so I constructed a wooden frame as far away from the original window as possible. The frame was designed to accommodate two panes of 6 mm glass. Effectively therefore I would end up with triple glazing.
I chose 6 mm glass because there was a steep price hike for thicker glass, but obviously the thicker the glass, the more sound insulation you will get out of it.
Following the advice of a BBC acoustics manual I set the panes in a flexible mastic so that they were not in firm contact with the frame. Prior to fixing the panes, I lined the reveal with carpet to absorb any sound energy bouncing around between my secondary window and the original window.
I can proudly say that the results were entirely satisfactory for my purpose. I suspect that the traffic noise mentioned in the question would require a more heavy-duty treatment, but the principles are the same.
I did learn a few things along the way however...
In conclusion, I can say that it is a fairly simple matter to improve the sound insulation of a window. Be careful with the glass, and pay attention to the points mentioned above.
P.S. Don't forget that when you have sealed the window, you have also sealed off a source of ventilation in the room. You'll have to get your fresh air from a different source.
P.P.S. Many studio windows use angled panes. In theory this should be a good idea, but my BBC manual reckons that it doesn't make much of a difference in practice. Even so, it wouldn't have hurt to angle the panes, but I didn't think my carpentry skills would have been up to it.