There usually a desirable characteristic. Electric guitars use a

There are
few technological advancements that made a bigger impact on pop music and culture
in the last 100 years than the invention of the electric guitar. From the
advent of the big band in the early 20th Century, guitarists
struggled to remain audible over the loud brass and woodwind sections, and
microphonic amplification gave a poor quality of sound when playing live. The result
of this problem was the electric guitar, invented in 1931. Since then, the
instrument as had a profound effect on music, playing a key part in genre
development as well as becoming one of the most salient icons of the modern
era. While the instrument is high profile, most guitarists don’t know the
basics of their instrument, and that is the aim of this essay.

All string instruments rely on standing
waves to produce sound. The strings are stretched from the bridge (on the body
of the instrument) to the nut (at the top of the neck). Their linear mass
density is selected to be appropriate for the fundamental frequency desired for
the open (unfretted) string, and they are tightened or loosened in accordance
with the following formula:

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where

 denotes the fundamental frequency,  denotes the wave speed,  denotes the tensions of the string,  denotes the length of the string and  denotes its linear mass density. The tightness
of the strings is controlled using “machine heads” attached to the headstock of
the guitar. These use a system of gears to wind the strings around a peg, and
rely on static friction to keep them at the desired tension.

On an acoustic string instrument, the
vibrating strings disturb the air molecules in their surroundings, creating
propagating sound wave. These waves are then amplified by the hollow body of
the instrument, as in an acoustic guitar or violin. However, since electric
guitars use electromagnetic induction for amplification, acoustic resonance is
not usually a desirable characteristic.

Electric guitars use a form of electromagnetic
transducer called a pickup to amplify
the sound produced by the string. Put simply, they consist of magnets with a
coil of wire around them, but there are some variations thereof. The two most
common pickups are referred to as single coils
and humbuckers. Single coil pickups
are the most basic form, and consist of a row of six magnets (one for each
string) wrapped in a wire coil. The magnets are often made of an alloy of
aluminium, nickel and cobalt referred to with the acronym alnico. Alnico has a high resistance to loss of magnetism, a
property known as coercivity, which makes it suitable for the permanent magnets
required in an electric guitar. Pickups are effectively alternating current
generators. The magnetic field produced by the magnets is disturbed by the
charged particles moving in the strings. As stated in Faraday’s law, the electromotive
force produced is equal to the negative of the product of the number of turns
in the coil and the derivative of the magnetic flux with respect to time. Higher
output pickups can be made by increasing the number of turns in the coil or
using more powerful magnets.

When the electric guitar was in its
infancy, single coil pickups were the only option for musicians. Unfortunately,
they are prone to audible interference, known as hum. The coil acts as an antenna, and any varying magnetic fields
in the nearby area are amplified. This causes undesirable noise. However, humbuckers
comprise two rows of six magnets arranged with opposite polarity to one another,
each wrapped in a separate coil. They are connected out of phase, in either
series or parallel. Due to the 180o phase difference, interference picked
up by one coil is of opposite polarity to that of the other, so the noise
signals cancel upon combination. String vibrations are picked up as usual and,
due to the opposite polarities of the magnets, the currents they induce in each
coil are 180o out of phase. This cancels out the phase difference in
the wiring, so the signal from the strings is summed. Despite this advantage,
single coil pickups remain as popular as humbuckers, as many guitarists prefer
their “brighter”1 sound.