There arefew technological advancements that made a bigger impact on pop music and culturein the last 100 years than the invention of the electric guitar. From theadvent of the big band in the early 20th Century, guitaristsstruggled to remain audible over the loud brass and woodwind sections, andmicrophonic amplification gave a poor quality of sound when playing live. The resultof this problem was the electric guitar, invented in 1931. Since then, theinstrument as had a profound effect on music, playing a key part in genredevelopment as well as becoming one of the most salient icons of the modernera. While the instrument is high profile, most guitarists don’t know thebasics of their instrument, and that is the aim of this essay.All string instruments rely on standingwaves to produce sound. The strings are stretched from the bridge (on the bodyof the instrument) to the nut (at the top of the neck). Their linear massdensity is selected to be appropriate for the fundamental frequency desired forthe open (unfretted) string, and they are tightened or loosened in accordancewith the following formula: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 tightnessof the strings is controlled using “machine heads” attached to the headstock ofthe guitar. These use a system of gears to wind the strings around a peg, andrely on static friction to keep them at the desired tension.On an acoustic string instrument, thevibrating strings disturb the air molecules in their surroundings, creatingpropagating sound wave. These waves are then amplified by the hollow body ofthe instrument, as in an acoustic guitar or violin. However, since electricguitars use electromagnetic induction for amplification, acoustic resonance isnot usually a desirable characteristic.Electric guitars use a form of electromagnetictransducer called a pickup to amplifythe sound produced by the string.
Put simply, they consist of magnets with acoil of wire around them, but there are some variations thereof. The two mostcommon pickups are referred to as single coilsand humbuckers. Single coil pickupsare the most basic form, and consist of a row of six magnets (one for eachstring) wrapped in a wire coil.
The magnets are often made of an alloy ofaluminium, nickel and cobalt referred to with the acronym alnico. Alnico has a high resistance to loss of magnetism, aproperty known as coercivity, which makes it suitable for the permanent magnetsrequired in an electric guitar. Pickups are effectively alternating currentgenerators. The magnetic field produced by the magnets is disturbed by thecharged particles moving in the strings. As stated in Faraday’s law, the electromotiveforce produced is equal to the negative of the product of the number of turnsin the coil and the derivative of the magnetic flux with respect to time. Higheroutput pickups can be made by increasing the number of turns in the coil orusing more powerful magnets.When the electric guitar was in itsinfancy, 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 fieldsin the nearby area are amplified. This causes undesirable noise. However, humbuckerscomprise 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 eitherseries or parallel. Due to the 180o phase difference, interference pickedup by one coil is of opposite polarity to that of the other, so the noisesignals cancel upon combination. String vibrations are picked up as usual and,due to the opposite polarities of the magnets, the currents they induce in eachcoil are 180o out of phase.
This cancels out the phase difference inthe wiring, so the signal from the strings is summed. Despite this advantage,single coil pickups remain as popular as humbuckers, as many guitarists prefertheir “brighter”1 sound.