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Bone conducting headphones sound like strange gadgets, but they're surprisingly easy to build. This video from Tinkernut walks you through the basics of speaker technology, and in the first minute or two tells you how to build a bone-conduction speaker you could easily house in a hollowed out pair of on-ear headphones or earmuffs.
The full video is well worth a watch if you've ever been curious how speakers work or how to build your own, but the bits regarding bone conduction start around 58 seconds in. You'll need a few things for the project, namely a small DC motor and an old pair of headphones, but the rest can be done pretty easily with what you have around the house. When you're finished, you'll be able to press the speaker to the area behind your ear and turn what sounds like meaningless vibrating into actual audible tones you'll be able to hear even in loud environments.
Hit the link below to watch the full video and see the parts list for this and the "cheap speaker" outlined later in the video.
World's Cheapest Speaker | Tinkernut