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Acoustic and Electric Guitars
Transcript of Acoustic and Electric Guitars
The Physics of Music
A guitar uses vibrating strings to generate tones.
Guitar's sound produced like so:
front of guitar's body
makes the sound loud enough for us to hear
sometimes "f" shaped, like violins
lets the sound out
acts as anchor for one end of six strings
part that the strings rest against
An electric guitar sense a vibrating string electronically using a magnetic pickup underneath the strings on a guitar's body.
affect the sound of the Guitar
upper bout accentuates higher tones
lower bout accentuates lower tones
face of the neck
contains the frets
metal piece cut into the fingerboard at specific intervals
by placing finger on fret, change length of string that vibrates
allows player to increase or decrease tension in string
tune the instrument
grooved to accept the strings
acts as the other end of the string (counterpart of the saddle)
More on Strings and Frets
length of string
amount of tension
weight of string
"springiness" of material
frequency depends on:
spaced out so right frequency is produced when string is held down at each fret
magic number: 17.817
if neck is 26 inches long,
1st fret: 26/17.817=1.46 inches from nut
A Guitar's Sound
vibrations transmitted to saddle
saddle transmits vibrations to soundboard
soundboard and body amplify sound
sound comes out through sound hole
Things that give it that distinctive "guitar" sound:
shape and material of soundboard
shape of body
the fact that it uses strings
same six strings
tuned with tuning pegs
The differences start showing up when you look at the body.
One example of a pickup:
bar magnet wrapped in thin wire
vibrating strings cause vibration in magnetic field
vibration in magnetic field causes vibrating current in wire
Another example of a pickup:
pole piece (separate magnet) for each string
sometimes screws so can be adjusted
closer to string, stronger signal
The pickup's coil sends signals through a simple circuit.
upper resistor and capacitor form a low-pass filter
cuts out high frequencies
adjust resistor, control which frequencies get cut
controls the amplitude of the signal that reaches the jack
Many guitars have multiple pickups at different points on the body.
each pickup has distinctive sound
pickups can be paired to produce more variations
either in-phase or out-of-phase
Amps and Distortion
The job of an amp is to take a guitar's signal and boost enough to drive a speaker.
An amp typically has three parts:
boost the signal enough for the next part
A power amplifier
An electric guitar's amp is very different from a stereo amp.
stereo amps are meant to be transparent:
amplify sound with very little distortion
many electric guitarist want distortion
it's part of the guitar's sound
a lot of amps are designed so the guitarist can control the level of distortion
If the sound coming out of the amp and the speaker is loud enough, it can make the string vibrate.
Distortion results when the signal in an amps circuitry is too powerful.
The musician can hit a note with the guitar, and the amp will cause that string to continue vibrating indefinitely.
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