Physics of Guitar
Home History Acoustic
vs Electric Producing Tone
Acoustic
Amplification Electric
Amplification Bibliography
Producing Tone
- Sound is a rapid change in air pressure.
- We get different Tones by varying the rate of change of air
pressure, or the frequency.
- By vibrating a string, we can create a change in air pressure,
creating a sound wave.
WAVES
(briefly)
- Two types. Transverse and Longitudinal.
- Transverse waves (like those seen on a guitar string). The
string itself moves perpendicular to the motion of the wave.
- Longitudinal waves (sound waves). The wave is a series of
compressions and rarefactions (decompressions) of the medium (air)
parallel to the direction of the wave.
- In general, wave can be described by their velocity (v),
frequency (f), and wavelength.
v=f(wavelength)
where v=speed of sound (in air), which is approx. 343 m/s.
Guitars take advantage of the fact that a string under tension vibrates
at a certain frequency. Controlling this frequency is the tricky
part. The frequency of vibration of a string depends entirely on
the
properties of the string, including length (L), tension (T), mass (m),
and flexibility or stiffness (similar to spring constant, k, in Hooke's
Law of Springs).
- These are related by v=Sqrt[T/(m/L)] where
(m/L) is the linear
mass density and v is the speed of the wave moving down the
string.
- By setting these two equations equal to each other, we find
f=Sqrt[T/(m/L)] / (wavelength)
which we can use to tune the guitar to a desired frequency.
- By using strings of different mass, and adjusting the tension
(tuning), a guitar can be made ready to play.