How a Guitar Works

How a Guitar Works

A typical guitar has six strings. These are all of the same length,

and all under about the same tension, so why do they put out sound of

different frequency? If you look at the different strings, they're of

different sizes, so the mass/length of all the strings is different.

The one at the bottom has the smallest mass/length, so it has the

highest frequency. The strings increase in mass/length as you move up,

so the top string, the heaviest, has the lowest frequency.

Tuning a guitar simply means setting the fundamental frequency of each

string to the correct value. This is done by adjusting the tension in

each string. If the tension is increased, the fundamental frequency

increases; if the tension is reduced the frequency will decrease.

To obtain different notes (i.e., different frequencies) from a string,

the string's length is changed by pressing the string down until it

touches a fret. This shortens a string, and the frequency will be

increased.

Wind instruments and longitudinal standing waves

Pipes work in a similar way as strings, so we can analyze everything

from organ pipes to flutes to trumpets. The big difference between

pipes and strings is that while we consider strings to be fixed at

both ends, the tube is either free at both ends (if it is open at both

ends) or is free at one end and fixed at the other (if the tube is

closed at one end).

A pipe organ has an array of different pipes of varying lengths, some

open-ended and some closed at one end. Each pipe corresponds to a

different fundamental frequency. For an instrument like a flute, on

the other hand, there is only a single pipe. Holes can be opened along

the flute to reduce the effective length, thereby increasing the

frequency. In a trumpet, valves are used to make the air travel

through different sections of the trumpet, changing its effective

length; with a trombone, the change in length is a little more

obvious.