David Clark H10-60 noise canceling aviation headset & M-7A microphone, $3.

Just about everything related to aviation and aircraft and flying means big money, and these headsets are no different. You really should take a few minutes to learn at least a bit about aviation headsets, because they spell cash. And since David Clark is the likely best known aviation headset in the world, you may want to start here!

David Clark headsets appear regularly, and are such a great opportunity because of their deceptive looks. Unknowing sellers don't think twice about unloading what they mistakenly assume are just old stereo headphones The presence of that little microphone never seems to make them wonder about what these headsets are really for. Oh well, in another beautiful case of mistaken identity, an expensive piece of equipment is handed off for a few dollars. You must understand that most people have no idea whatsoever what aviation headsets are, what they do or how much they cost.

An interesting part of this headset is the M-7A noise canceling microphone. When a pilot is flying an aircraft, he has to communicate with various ground controllers via his radio, as well as with his copilot, if he has one. If you've ever flown in a light aircraft, you know that they're nothing like those big, whisper-quiet jumbo jets. Small planes are loud! Imagine driving down the road in your car, trying to communicate with someone on your CB radio and speak with your passenger at the same time. Oh, and there's also a lawnmower running full blast in your back seat!

Now you get the idea. Some sort of noise-canceling headset would obviously help in such a noisy environment, wouldn't it? The speakers inside the headsets would ensure that everyone would be able to hear everyone else over the noise, and the microphones in each headset would ensure that... wait a minute... no matter how well your headsets were able to keep out external noise, whenever anyone keyed his mic to say something, the only thing the microphone would pick up was that confounded lawnmower blasting away in the back seat!

The trick here is to use a microphone that filters out everything except for the voice that's right in front of it, which is just what the little M-7A microphone on our David Clark headset does. When the person wearing the headphones keys up to speak, his voice is the only thing anyone hears. The pilot, copilot and passengers can speak comfortably with one another, and the pilot can communicate easily with the ground controllers.

As far as testing a pair of these headphones goes, you probably won't be able to unless you're a pilot or know one who can test them for you. But that's not really a problem. First of all, these headphones are really rugged and are unlikely to be internally damaged unless there's some really obvious external damage. Second, just like so many other pricey items you're going to find, if you buy correctly, it's worth taking the small risk that they don't work. If they're sent back to you as not working, just relist them as 'not working.' My friends and I have sold plenty of these David Clark headsets, and we've never had a single pair come back as inoperative.

There are all sorts of various models of David Clark headsets floating around out there, from the older and cheaper to the newer and more expensive. So as usual, the trick is not to become an expert in these headsets, but to know what they look like so that when you see them for a few dollars, you'll know to jump on them.

This pair of David Clark H10-60 aviation headsets sold on eBay for $225.