Electronic Devices: How Electric Guitars Work

Electric guitars work by picking up and amplifying the tones generated by guitar strings as they vibrate.

In order to understand how an electric guitar works, it may be best to examine the relationship between the basic instrument and the electronic amplification system.

A standard acoustic (non-electric) guitar is essentially a collection of six wire strings held in tension over a hollow box and a fretboard. Each string is tuned to vibrate at a specific frequency. These frequencies correspond musically to the notes E, A, D, G, B and E. By depressing the strings on the fretboard, trained guitarists can produce the notes between these open strings. Whenever a string or strings is plucked or strummed, the strings send out soundwaves in all directions, including a circular hole in the body of the guitar. Some of the soundwaves bounce around the hollow interior and exit through this hole. The result is a slight amplification of the string's tone. Some acoustic guitars may have metallic cones called 'resonators' installed in the body. These resonators may further amplify the soundwaves and add a brighter tone. Acoustic guitarists can affect the loudness and softness of a guitar's dynamics through technique, but in general an acoustic guitar has definite limitation when it comes to performance volume.

The other basic system behind an electric guitar is electronic amplification. Every measurable sound creates a soundwave, but these waves may not contain enough energy to reach our ears. What may sound loud from inches away may not register at all a few hundred yards away. Electronic amplifiers such as microphones pick up the soundwaves close to their source. These waves cause sensitive magnetic fields to vibrate, but the impulses are still faint. The vibrations are 'amplified' by stronger electronic currents in a receiver and delivered to a larger magnetic field behind a cone-shaped speaker. The impulses from this larger magnet cause the speaker's cone to recreate the original sound, only this time it's much louder. The sound of a human voice or guitar or any other amplified sound is not the authentic sound of the source, but an electronic duplication.

One interim solution to amplifying an acoustic guitar is to place an electronic microphone near the guitar's soundhole and amplify the sound through a receiver and speakers. But the result is not the same as an electric guitar. The sound is picked up ahead of the vibrating strings and the basic acoustic sound is not affected. Amplifying an acoustic guitar may help with its volume, but it does not change the tone appreciably.

A combination of a modified acoustic guitar and specially-designed microphones lead to the first truly electric guitar.

An electric guitar has several noticeable differences when compared to a standard acoustic model. An electric guitar may have a hollow body, but no soundhole as such. The strings are not always held as far away from the fretboard on an electric guitar. Electric guitars may also contain a 'whammy bar'- a device designed to allow the player to bend the tone of the strings by literally loosening the bridge. Electric guitars also contain several electronic devices called 'pick-ups' under the strings, as well as some control knobs for changing the overall tone of a string. Electric guitar bodies may also be designed for dramatic appeal or a better balance. They are often decorated more elaborately than acoustic guitars.

An electric guitar works on the principles of vibration and amplification. When a string is plucked on an electric guitar, it vibrates at a specific rate- the higher the note, the faster the vibration. The guitar is attached to an electronic amplifier by a two-way umbilical cord equipped with a quarter-inch plug, also known as an RCA plug. This cord carries electrical impulses in two different directions. Power from the amplifier unit energizes the electronic pick-ups located on the guitar body under the strings. Some guitars only have one pick-up, while others may have as many as three or four. These magnetic

devices are sensitive to the vibrations of the strings. The small impulses sent out by the strings are not easily heard by the human ear whenever the guitar is unpowered, but the pick-ups are sensitive enough to send out their own electronic pulses down the cord and into the amplifier.

Inside the amplifier, these electronic impulses are strengthened and sent to a powerful magnet located behind a cone-shaped device which recreates the vibrations of the original sound source. Because the magnet receives a stronger signal from the amplifier, the sound is louder. The vibrations from the cone are directed outward and the listeners get an electronic reproduction of the original guitar sound. Amplifiers with even more powerful magnets and bigger cones will sound even louder, which explains the huge speaker arrays at most rock concerts.

Meanwhile, the guitarist has several options because the signal is electronic instead of purely acoustic. The pick-ups are placed strategically on the guitar- one near the bridge picks up more distorted vibrations than one placed closer to the fretboard, for example. By selecting which pick-ups are active and which are turned off, the guitarist can create a variety of sounds. An upbeat rock song could benefit from the brighter sound of one pick-up near the fretboard while a darker blues song might sound better with all three pick-ups causing some distortion. Controls on the amplifier or the guitar itself can also change how much of the bass tones will be amplified or how sensitive the pick-ups will be. Experienced electric guitarists learn how to manipulate the pick-ups and control knobs to create a specific sound.

Electric guitar sounds can also be manipulated by various electronics added to the guitar or to the amplification system itself. Tones can be deliberately overloaded, causing a distortion or 'overdrive' effect. An electronic device can recreate and hold a guitar's note for several seconds, causing a delayed effect the guitarist can play against. Other effects such as echoes or fuzz can be controlled through footswitches at the whim of the player. Some guitarists will also place a vocal microphone in front of a small guitar amp in order to patch the sound directly through a mixing board. Wireless devices will convert the electronic impulses from the pick-ups to radio waves picked up by a receiver.

More recent innovations have given guitarists the ability to use their guitars as the triggers for advanced digital sounds. In the same way that electronic synthesizers and keyboards can duplicate strings and horns, modern electric guitars can be manipulated to sound like any other instrument in the orchestra. Specific strings can be assigned different 'voices' for special effects. Beginning electric guitarists can also set up a digital guitar to make complicated chord formations much easier. The standard electric guitar should still be around for many years to come, but the future may belong to this new breed of digital guitars.

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