Open back usually results in more natural sound, but they leak sound in and out. This means you probably can’t use them in a library or a plane flight since the sound of your music will leak out and disturb the people around you. You also can’t use them on loud public places since noise from the outside will disturb your music. Therefore, even though open back would give you more natural reproduction, for these reasons their use is limited to mostly at home or in the office (if you have your own space that is).
In early powered radios, the headphone was part of the vacuum tube's plate circuit and carried dangerous voltages. It was normally connected directly to the positive high voltage battery terminal, and the other battery terminal was securely grounded. The use of bare electrical connections meant that users could be shocked if they touched the bare headphone connections while adjusting an uncomfortable headset.
Over-ear and on-ear headphones effectively block out outside sounds, allowing you to hear your music or whatever else you're listening to crisply and without distraction. Over-ear headphones are sometimes known as full-size headphones because they completely envelop the wearer's ear. This results in what's known as passive noise reduction, which makes these some of the most-preferred headphones available. The only drawback is that your ears and the skin around your ears can get warm and sweaty. These are usually the heaviest type of headphones.