|MadSci Network: Physics|
The answer is a qualified "yes". Although it is true that a window transmits some sound, it also absorbs some sound. So, the amount of sound that gets through will be diminished. This means that a larger-than-normal parabolic dish will be needed by the eavesdropper, to compensate for the diminished sound. Perhaps you don't know this, but there exists a much less obvious way to eavesdrop on the sound coming through a window, than using a parabolic microphone. This trick involves shining a low-power infrared laser beam (invisible!) against the glass, and catching the reflected beam with an appropriate SMALL sensor. It happens that the vibrating glass (caused by sound waves) distorts the reflected laser light in a way that is fairly easily translated back into good-quality sound waves, for the benefit of the eavesdropper. With respect to protecting your in-house conversations from eavesdroppers, several different things can be done, and each is somewhat effective. If you could implement all of them, you will probably obtain reasonable security from remote eavesdroppers ("bugs" that are planted are an altogether different problem, of course). First, get double-paned or even triple-paned windows. EACH layer of glass, after all, will diminish the sound that passes through it. Next, get FULL curtains, both the relatively thin type near the glass, and the fairly heavy-cloth type that can block the light. Curtains will also absorb sound on its way through the windows, of course. Finally, you can put working (not decorative!) storm shutters outside the house. Their job is to protect the glass during storms, but they also can help diminish escaping sounds. (And shutters, at least, can also block laser beams)
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