Previously,
we have learned that strings vibrate, producing
sound waves, which is what gives the guitar its
purpose. However, if it weren’t
for the body of a guitar, the vibration of the
strings would barely be audible.
The body of the guitar amplifies the sound of
the strings, making it possible for it to reach
the ears of the listeners.
Acoustic Amplification
When a player plucks the
guitar strings, the strings
vibrate, which transfers the mechanical energy
down the strings to the guitar's bridge,
which is attached to the guitars body. This
transfer of energy causes the top
plate, also called the soundboard, to vibrate
as well. The soundboard is most
often made of a thin piece of wood, which is
designed to easily vibrate. The
vibration of the soundboard then causes the
air inside the guitar cavity to
vibrate. When the molecules of air closest to
the soundboard start vibrating,
they bump into the other particles around
them, and soon there is a
symphony of dancing air molecules inside the
guitar. This is where the sound
hold finds its purpose. The sound hole is
where all the vibrating air escapes
from the guitar’s body and is projected out,
reaching the ears of the
listeners.
Electric
guitar work a bit differently than their
acoustic cousins. The main difference
is that electric guitars have a solid wood
body, and instead of using a soundboard
for amplification, they rely on electronic
pickups. The pickups do their name
justice, and “pick up” the sound vibrations
from the plucked string, and
convert these vibrations into electronic
signals that are then read by an
amplifier. The pickups are essentially
electromagnets, consisting of a bar
magnet wrapped in fine conducting wire. The
vibrating steel strings above the
pickup causes a change in magnetic flux in the
system. According to Lenz’s Law, "there is an
induced current in a closed, conducting loop
if and only if the magnetic flux through the
loop is changing" (Knight 972). This change in
the
flux through the closed loop generates a
voltage, or emf, by Faraday’s Law.
This produced voltage then sends the induced
current to the amplifier.
Once
the induced current has traveled to the
amplifier, it now can be manipulated or
distorted in any way that the musician desires
using a series of different
resistors, transistors, and other elements of
electrical circuitry. This
current then vibrates the diaphragm of the
speaker inside the amp to produce a
frequency that is identical to that of the
original plucked string.