Introduction

• Given that some audio speakers can cost hundreds of thousands of dollars, you might think that the science behind speakers is equivalent to rocket science. While meticulous design and engineering play a role in bringing that million-dollar sound, the physics of speakers is actually quite easy to understand. There are really only a few things at play.
  
  

Audio Signal

• In order to produce sound, audio speakers need an input signal. The signal originates at your audio source, which can be anything from a CD player to a television. The signal is sent to your receiver, where it is decoded, split into the appropriate channels (speakers) and powered. The signal needs to be powered in order to drive the speakers effectively enough to produce the sound that you hear.
  
  

Crossover

• In the average stereo setup in which one receiver or amplifier is used to power all speakers, a crossover circuit in the speaker routes the frequencies to the appropriate drivers. The number of dedicated drivers that your speaker has will vary depending upon its design, but all drivers break into three basic categories: woofer (low frequencies), tweeter (high frequencies) and mid-range (mids). The specific frequencies that serve as cutoffs between the drivers vary by speaker, but its the crossover circuit's job to get the frequencies where they need to go.
  
  

Drivers

• The operation of each of the aforementioned drivers is basically the same; they just use different materials, sizing and design to deliver the appropriate frequencies. A speaker driver consists of a voice coil, diaphragm and a stable magnet. The voice coil is an electromagnetic coil through which the electrical audio signal flows. The flow of electricity through the coil creates a magnetic field. The audio signal is alternating current (AC) and is constantly changing directions. When the current changes directions, the electromagnet's north and south poles flip flop. This change of direction and polarity is occurring rapidly many times and is based on the frequency contained within the audio signal. When the polarity of the magnet changes, it is constantly either attracted to or repelled from the stable magnet. In essence, this constant cycle of magnetism causes the coil to vibrate back and forth. The diaphragm is the large dome or cone that is connected to the voice coil. It vibrates with the coil. When the diaphragm vibrates, it vibrates the air molecules directly in front of the speaker and sound waves are created that you hear as the music or audio programming that you are listening to. The speaker just turned electrical current into audible sound.