How Loudspeakers Work
From amplifier current to sound pressure: the moving-coil driver, why cabinets matter, crossovers, and the physics that limits every speaker no matter its price.
A loudspeaker converts electrical current into air pressure. Nearly every speaker you have ever heard is a moving-coil dynamic driver doing one simple thing: an audio-frequency current flows through a coil suspended in a magnetic field; the coil and attached cone move; the cone pushes air in the pattern of the current. Everything else in speaker engineering is the fight to make that motion accurate across the audible range.
The driver
The motor is voice coil + permanent magnet: current direction reverses with the signal, force follows the cross-product rule, and the coil strokes in and out. The cone's job is to couple that motion to air efficiently, which is why cones are stiff, light, and shaped the way they are. Frequency response divides the labor: woofers (large, heavy cones, big excursions) move enough air for bass; tweeters are small and light to move fast enough for high frequencies. A crossover network routes each band to the right driver — this is why a two-way speaker is really two speakers.
Enclosure and directivity
An unbaffled cone short-circuits itself: the pressure wave from its front cancels the suction from its back at low frequencies. A baffle or enclosure delays or absorbs the rear wave; sealed boxes trade efficiency for tight transient response, ported (bass-reflex) boxes tune a Helmholtz resonance for extra bass from the port, and transmission lines exploit the wave behavior directly. Cabinet resonances, cone breakup modes, and diffraction set the honest limits of what the driver reproduces.
The limits
A driver cannot be simultaneously small (for high frequencies), light (for acceleration), and stiff (for low distortion) — hence multi-driver designs. Distortion, off-axis response, and room interaction dominate what you actually hear, which is why room acoustics and placement routinely matter more than the last price tier of the speaker. Related reading: wave-particle duality is unrelated — the closer analog is doppler effect for why motion shifts the pitch you hear.
Tags
acoustics loudspeakers physics sound