[George Trimble] likes to build crystal radios. The original crystal radio builders used high impedance headphones. In modern builds, you are as likely to include a powered amplifier to drive a speaker or normal headphones (which are usually around 4 to 16 ohms).
[George] builds his own speakers using chile cans, some wire, a few magnets, part of a Pepsi can (we are pretty sure someone will leave a comment that Coke cans sound better), and the iron core out of an audio transformer. You can see a very detailed video of the process, below.
There is a little woodworking and hot gluing involved. The result is decidedly homemade looking, but if you want to say you built it yourself (or, if you are a prepper trying to get ready to rebuild after the apocalypse and you can’t find a cache of headphones) this might be just the ticket.
Most of the headphone hacks we see start with a pair of headphones. That’s a bit tautological, but the goal is usually to add features, not make the whole thing. It does give you some hacker cred, though, to be able to look at the other guy’s radio and say, “Oh. I see you used commercial headphones.”