There’s obviously no more important piece of audio equipment than the speaker – the way we actually hear recordings or the amplified signal from microphones on stage. But unless you make speakers for a living, you may not have much cause to open one up and study the insides – even though it might be nice to understand a bit about them.
There are many different kinds of speakers; PA speakers, studio monitors, theater speakers, stage monitors, active speakers (with an amp built-in), car speakers, headphones, and so on; but they all share a basic design, so here’s a simple introduction to the anatomy of a speaker.
Types of speakers
Loudspeakers come in two basic flavors: one speaker per cabinet – as in Carvin Audio’s QX5A 3-Channel Near Field Monitor - or multiple speakers in one cabinet, such as Carvin Audio’s SCX12A 1000 Watt Active Stage Monitor/Main. These “speakers within a speaker” are referred to as drivers.
Multiple-speaker cabinet arrangements will either be two-way or three-way. In a two-way system, low frequencies are handled by one or more large drivers called woofers, and high frequencies are handled by one or more smaller drivers called tweeters. In a three-way system, a third driver (or set of drivers) handles mid-range frequencies and is either referred to as a mid-range driver or a squawker. Rarely, speaker systems include another driver called a super tweeter, which produces very high frequencies – sometimes even out of the range of human hearing.
In two-way and three-way speaker systems, a crossover is used to split the signal into low and high frequencies (low, mid, and high for three-ways), sending low frequency information only to the woofer and high frequency information only to the tweeter.
Theater speakers, most home stereo speakers, studio monitors, and many kinds of PA speakers are two or three-way speaker systems, whereas guitar cabinets are generally a one-way system because they use one driver (or several of the same kind) which reproduces a frequency spectrum that is desired for the instrument.
A subwoofer is a special speaker designed to reproduce only low frequency sound.
Speaker Parts
Several parts make up the design of any speaker driver:
Cone (or diaphragm)
The cone is the lightweight part of the speaker that moves, creating sound waves.
Voice coil
The voice coil is attached to the cone and receives an electrical signal representing an audio waveform. This electric current creates a magnetic field which in turn turns the coil into a variable electromagnet. This mechanism is alternately charged positively and negatively, which attracts or repels it from a fixed magnet. The voice coil moves, and since it’s attached to the cone, the cone moves as well, displacing air and creating a sound wave.
Magnet
The magnet creates a fixed magnetic field, which is what allows the changing polarity in the voice coil to create physical motion.
Top plate, backplate, pole
These are conductive parts which concentrate magnetic energy on the voice coil.
Surround and spider
The spider is a fibrous material and surround is a flexible ring. Together they form a suspension system that allows the cone and voice coil to physically move forward and backward, but not side to side.
Flex wires and wire terminals
These wires deliver electrical signal (audio) to the voice coil.
Dust cap
The dust cap (a round nub, visible in the center of the cone from outside the assembly) prevents debris, dust, and especially metal pieces from entering the gap between pole and magnet and interfering with the voice coil.
Basket (or frame)
The basket simply holds everything together and attaches it to the cabinet.
Cabinet
The cabinet is the box the loudspeaker is in. The size and ports (openings) or lack thereof determine to a large extent the overall performance of the speaker system.
That is speaker anatomy in a nutshell. There are many variations, but all speakers have this basic design in common.
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