Headphones are a pair of transducers that receive electrical signals from a media player or receiver and convert them into audible sound waves using speakers placed close to the ears. Originally used for telephones and radios, headphones are now widely used in mobile phones, portable music players, radios, portable game consoles, and digital audio players due to the prevalence of portable electronic devices.
Sound is produced by vibration. The working principle of headphones is the same as that of speakers: a coil in a permanent magnetic field is connected to a diaphragm. Driven by a signal current, the coil drives the diaphragm to produce sound, converting the input audio electrical signal into mechanical vibration, which is how we hear music through headphones.
Faraday's law of electromagnetic induction states that changes in magnetic flux generate an electric current. For example, when a conductor in a closed circuit moves through a magnetic field, cutting magnetic field lines, an electric current is generated-simply put, magnetism generates electricity. Conversely, an electric current also generates a magnetic field. The working principle of headphones is that changes in current generate a changing magnetic field, and the movement of the magnet causes the diaphragm to vibrate, thus producing sound.
There are two magnets inside headphones. One component is the strong magnetic magnet shown in the image below, a permanent magnet fixed to the headphone frame and firmly glued in place. The other component is the voice coil connected to the diaphragm, an electromagnet that only becomes magnetic when energized and is movable.
Sound is produced by the diaphragm pushing air to vibrate. When an audio current flows through the headphone cable and then through the red voice coil inside the headphone (as shown in the image below), a changing magnetic field is generated. This magnetic field interacts with the permanent magnet inside the headphone, causing the voice coil to vibrate with varying amplitudes, which in turn causes the diaphragm to vibrate, producing different sounds.
The symbol for headphones is "BE". Based on their structural form, headphones can be categorized as ear-hook, over-ear, helmet-style, stethoscope-style, in-ear, and handle-style, etc. Based on their transduction principle, headphones can be categorized as electromagnetic, electrodynamic, piezoelectric, and electrostatic, etc. Based on their usage, headphones can be categorized as broadcast headphones, voice communication headphones, and pilot headphones, etc.
