Want to find out if your neighbors are talking about you? You could always hack their webcam or turn your iPhone into a secret spy camera, but unless you have a key to their house, that could be tricky to do without getting caught.
With this DIY parabolic microphone (archived link) from the folks over at GBPPR (archived link), you can listen in from a distance and do your sleuthing without ever leaving the couch.
A parabolic microphone uses a parabolic reflector to focus sound waves onto a receiver. This makes it a lot more sensitive than a normal microphone (think of it like a satellite dish for audio). They're used for everything from sports broadcasting to nature recording to more nefarious purposes like eavesdropping and law enforcement.
To build your own, you'll need a parabolic reflector, which is the hardest part to find (GBPPR recommends eBay seller sdill471). For this setup, an aluminum wok lid was mounted behind the reflector with an L-bracket to keep it from flexing. You'll also need a 3.5" tweeter speaker and an electret microphone, which you can find at RadioShack. A low-noise amplifier circuit adds 40dB and can be put into "boost mode" to pick up even more. The whole thing is mounted on a standard camera tripod.
You'll need some minor circuitry skills, but overall, this isn't a super complicated build. You can find schematics as well as detailed instructions over on GBPPR (archived link) or from their zine (archived link). Check out the video to see it in action.
Wanna try a simpler version? You can turn an umbrella or megaphone into a lower-tech parabolic mic. Don't have either of those? The videos below show you how to hack one out of a bowl.
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