Introduction

• The voice coil of the speaker gets its name because it is an electromagnetic coil (wire around a piece of metal) that produces sound. The voice coil is the heart of the speaker and converts electrical current into audible sound waves.
  
  

Current and Magnetism

• The process begins with electrical current that is sent from the stereo amplifier. The current is routed to the appropriate speaker driver based on frequency by crossover circuitry within the speaker. Each driver contains similar construction, which is centered around a voice coil. The current flows through the wiring of the voice coil and creates a magnetic field. Because stereos operate on alternating current (AC), the current is constantly changing directions in the wire coil. The effect of the alternating current is that the polarity of the electromagnetic coil is constantly changing; the north and south pole are switching places as the current alternates direction.
  
  

Coil Movement

• The voice coil is located inside a circular magnet. This is a regular magnet with a constant north/south orientation. As the polarity of the voice coil changes, the coil is alternately attracted to and repelled from the stationary magnet causing it to move back and forth. The voice coil oscillates back and forth quite rapidly, and its movement is based on the frequency of the audio signal.
  
  

Diaphragm

• The voice coil itself does not produce the finished audio product. Attached to the voice coil is a diaphragm, generally a dome or cone. This is the large part of the speaker driver that you actually see when you pull off the grill. Since the diaphragm is attached to the voice coil, it oscillates with it and vibrates the air molecules directly in front of the speaker, passing the sound waves through the air to your ears. Since the vibrations of the voice coil and thereby diaphragm are based upon the frequency of the sound information contained within the signal sent from the amplifier, the sound waves that are produced are the replication of the audio source.
  
  

Drivers

• Most speakers contain multiple drivers to handle the different frequency ranges in music. Each driver operates with a voice coil as described above, but works only within a set frequency range. Tweeters are smaller drivers that are capable of oscillating very rapidly to produce high frequencies. Woofers are larger drivers capable of driving low frequencies. Mid-range drivers work to produce the frequencies that fall between the lows and highs.