How does an electromagnet make a telephone diaphragm vibrate and produce sound?

In a telephone receiver, the conversion of electrical signals into sound relies on electromagnetic principles. The device features a permanent magnet with pole pieces wound with coils of insulated wire, positioned near a diaphragm made of magnetic material.1

When fluctuating speech currents pass through these coils, they vary the magnetic attraction between the permanent magnet and the diaphragm. This changing magnetic force causes the diaphragm to vibrate in sync with the electrical fluctuations, effectively acting as a piston that pushes against the air to create sound waves that reproduce human speech.1

While early designs, such as those by Johann Philipp Reis, used an electromagnet to vibrate an iron needle against a sounding box, modern receivers utilize this refined electromagnetic system to achieve a wider frequency response, allowing for the clear transmission of vocal tones.12