They can fit in the nook of the human ear, projecting sound waves into the brain. They can also enclose the outer ear in a seal or lay flat against it. They are commonly made of plastic, magnets, nickel, and metal. They can cut off outside noise from the listener, or literally make them deaf over time. Young people often sport them as fashion statements, flashing the trendy brandname of their choice. They can be used as a defense mechanism in the office or subway, warding off unwanted attention. They have many practical applications, such as in the military.
Neighbors pass each other on the street, absorbed by the sound waves floating through their brain cavity. They do not acknowledge each other or even see each other. People fear the sound in the open air, they long for the personal audio escape. Personal interaction is dead, people can only communicate through the wires that reach their ears.
People standing on subways, glancing around nervously, with no auditory escape to occupy their minds. Gym-goers fighting over the music playlist played in the open air. On airplanes, there might be increased interaction, however, conversations are full of bickering over the lost technology as babies screech in the background. Runners on the street blast music from their phone. Military personnel and government officials operating switchboards are consumed in a noisy chaos as they lack the device to focus in on an individual sound.
Without headphones, people would listen to music in the open environment, creating a social audio experience. People would regularly gather around radios and stereos to enjoy the sound. Music would be projected on the subways, streets, and gym. Rooms and offices might be sound proof in order for the listener to play the music or radio station of their choice without interfering with others in the vicinity.