Headphones are personal audio devices worn on or around the ears to deliver sound directly from an electronic source (like a smartphone, computer, or audio player) to the listener. Their core function is to convert electrical audio signals into precise sound waves within an enclosed space near the ear. This process begins with drivers (transducers), typically dynamic drivers, planar magnetic, or balanced armature types, housed within each ear cup. These drivers contain a diaphragm that vibrates rapidly in response to the electrical signal, creating sound pressure waves. The ear cups themselves are crucial for sound quality: closed-back designs use sealed enclosures to provide passive noise isolation by blocking ambient sound and enhancing bass response, while open-back designs allow air and sound to escape, often resulting in a wider, more natural soundstage at the expense of isolation.