Custom Noise Cancelling Headphones
are a set of comercial headphone speakers built into an Ear Defender. They insulate the listener from external noise allowing him to enjoy the music without interferences. The idea was taken from a Makezine
post, and it is a very cheap way to implement an aproximation to what Bose or Sennheiser sell under the name of Noise Cancelling Headphones. I supose that sound quality is not as good as in those expensive headphones, but they are very usefull in the office, when you want to concentrate in your tasks.