Anyone who's ever been on a plane should have the impression that disposable headphones are provided on the plane and on every flight. Earbuds used on many flights are cheap and low cost. Promotional & Disposable Wired Earphones，Therefore, in order to prevent passengers from increasing the risk of skin diseases, airlines will advise passengers to take the earplugs away after use or arrange for staff to recycle the earplugs and dispose of them as garbage.
In the 1970s and 1980s, cost savings made it impossible for aircraft electrical systems to distribute audio signals to every seating area. Therefore, the earphones at that time were not the dynamic earphones that people often use now, and the earphones at that time were not driven by current.
The wires on the two units on the headphone structure are not signal wires, but two closed tubes. That is, the headphones of the time produced sound by vibrating the air inside the tube through two speakers.
like：
| 