Working Principle of Loudspeakers
A loudspeaker is an electroacoustic transducer that converts electrical signals back into sound, following the core energy conversion process: electrical → mechanical → acoustic energy. Taking the most common dynamic driver as an example:
Electromagnetic Drive
An alternating current from the audio amplifier flows through the speaker's voice coil. Positioned within the strong magnetic field of a permanent magnet, the coil experiences alternating mechanical forces according to the Lorentz force law (F = BIL), causing it to move back and forth.
Mechanical Vibration
The voice coil is rigidly attached to a cone/dome-shaped diaphragm. The axial motion of the coil drives the diaphragm to vibrate synchronously. Diaphragm materials (paper pulp, metal, or composites) balance lightweight properties with high rigidity, while the surround suspension provides restoring force to ensure linear motion and minimize distortion.
Sound Wave Radiation
As the diaphragm moves forward, it compresses air to create a high-pressure zone (compression wave); when retracting, it rarefies air to form a low-pressure zone (rarefaction wave). These pressure fluctuations propagate as longitudinal waves, ultimately perceived as sound by the human ear.
Frequency is determined by the rate of current change (diaphragm vibration frequency).
Loudness depends on the diaphragm's amplitude (current intensity).
Key Technical Features:
Magnetic field strength of the permanent magnet directly impacts drive efficiency (neodymium magnets: >1 tesla (T)).
Diaphragm geometry (cone/dome) optimizes sound radiation across frequency bands.
Crossover systems allocate full-range signals to dedicated tweeters/woofers.
This process achieves precise reconstruction of sound from electrical signals, making the loudspeaker the fundamental output component in the audio playback chain.