Electrodynamic speaker driver

For high fidelity reproduction of sound, multiple loudspeakers are often mounted in the same enclosure, each reproducing a different part of the audible frequency range.

Application of alternating current moves the cone back and forth, accelerating and reproducing sound under the control of the applied electrical signal coming from the amplifier.

The ideal material is rigid, to prevent uncontrolled cone motions, has low mass to minimize starting force requirements and energy storage issues and is well damped to reduce vibrations continuing after the signal has stopped with little or no audible ringing due to its resonance frequency as determined by its usage.

Chassis are typically cast from aluminum alloy, in heavier magnet-structure speakers; or stamped from thin sheet steel in lighter-structure drivers.

A typical suspension system consists of two parts: the spider, which connects the diaphragm or voice coil to the lower frame and provides the majority of the restoring force, and the surround, which helps center the coil/cone assembly and allows free pistonic motion aligned with the magnetic gap.

These diverse surround materials, their shape and treatment can dramatically affect the acoustic output of a driver; each implementation has advantages and disadvantages.

Polyester foam, for example, is lightweight and economical, though usually leaks air to some degree and is degraded by time, exposure to ozone, UV light, humidity and elevated temperatures, limiting useful life before failure.

The coil is oriented co-axially inside the gap; it moves back and forth within a small circular volume (a hole, slot, or groove) in the magnetic structure.

Due to increases in transportation costs and a desire for smaller, lighter devices, there is a trend toward the use of more compact rare-earth magnets made from materials such as neodymium and samarium cobalt.

[4] Speaker drivers include a diaphragm that moves back and forth to create pressure waves in the air column in front, and depending on the application, at some angle to the sides.

This cone, dome or other radiator is mounted at its outer edge by a flexible surround to a rigid frame which supports a permanent magnet in close proximity to the voice coil.

For the sake of efficiency, the relatively lightweight voice coil and cone are the moving parts of the driver, whereas the much heavier magnet remains stationary.

Other typical components are a spider or damper, used as the rear suspension element, simple terminals or binding posts to connect the audio signal, and possibly a compliant gasket to seal the joint between the chassis and enclosure.

The voice coil and magnet essentially form a linear motor working against the centering "spring tension" of the spider and surround.

In a multi-way loudspeaker system, specialized drivers are provided to produce specific frequency ranges, and the incoming signal is split by a crossover.

They are used among other places in audio applications such as loudspeakers, headphones, telephones, megaphones, instrument amplifiers, television and monitor speakers, public address systems, portable radios, toys, and in many electronics devices that are designed to emit sound.