How Loudspeakers And Headphones Work
Just as microphones do not require a playback system to work, loudspeakers and headphones do not require microphones to work.
How to loudspeakers and headphones work? Loudspeakers and headphones convert electrical energy (audio) into sound waves the propagate through the air (or other medium). Speakers/headphones have a diaphragm that moves according to the applied signal. The movement of the diaphragm creates the sound waves.
By the above description, we infer that speakers are basically large microphones in reverse. And this is true (of moving-coil dynamic microphones).
Most speakers are designed with a conductive coil that accepts electrical audio signals. This coil is surrounded by magnets and, therefore, a magnetic field. As the AC signal is applied to the coil, the magnetic field causes it to oscillate.
Since the coil is attached to the diaphragm, any audio signal applied to the speaker causes the diaphragm to move and sound waves to be produced.
Although microphone signals are often amplified and sent through speakers, we know that speakers can work without microphones.
Speakers often playback recorded audio (which could have been recorded with a microphone), but the record itself does not require any microphone for its signal to be sent to the speaker. On top of that, some recordings are made using absolutely no mics (synthesizers, etc.).
