The soundboard then vibrates the air that is inside the hollow body of an acoustic guitar, and this vibration of the air causes a natural amplification of the sound caused by the plucking of the strings.
Just as singing in a bathroom causes a louder and more resonant sound than when you sing in your garden, using this smaller, natural pocket of air behind the soundboard causes the increase in both volume and tone of the sounds and notes played.
Of course, the bridge is to be found on electric guitars as well as acoustic and classical ones, although for electric guitars the amplification is not achieved through the use of the pocket of air, as the body of an electric guitar is solid, with no resonating chamber.
But the bridge is still used to hold the strings in place on the actual body of the guitar.
The bridge of a guitar is therefore an essential component, and as with all components of a guitar, has not only undergone many variations in design over the long history of the instrument, but remains a component with many variations today.
For example, in some guitars there is a mechanism included which allows the physical raising or lowering of the entire bridge.
This raising and lowering of the bridge results in an increase in distance between the strings of the guitar and the fret board underneath.
The increased distance means that different playing styles can be adopted, with the ability to strike the strings made easier by a greater distance between strings and board, whilst a closer distance means that the strings are closer to the sound board, and a more heavy and amplified sound is produced.
The raising and lowering of the bridge can also be used as a way of fine tuning the sound or intonation of the instrument as well.
There are some bridges produced which are spring loaded, and include a device known as a whammy bar.
This whammy bar is an arm, usually removable, that allows the player to alter the pitch, or modulate it, by moving the entire bridge up and down during the playing of a note of chord.
The whammy bar is also referred to sometimes as a tremolo bar, and the very rapid changing in pitch of the notes or chord is usually referred to as the vibrato method in terms of music.
Today, most electric guitars come with a bridge that can be fine tuned for each individual string, in order to make sure that each string remains in tune both up and down the neck of the guitar.
If an individual string plays either sharp or flat when struck, then, in some cases using a screwdriver, the bridge can be adjusted for that one string alone, to bring it back into correct tune.
Because each individual string on a guitar is stretched a great deal, and is constantly being pressed, and thereby slightly stretched or distorted during playing, over time strings can become slightly longer.
Although not clearly noticeable, this can result in a string sounding slightly sharp, and so by adjusting the height of the bridge for that string, it can be flattened enough to retune it.
It is for this reason that the length of strings on a guitar are clearly longer than the length of the guitar itself, to allow for the adjustment of each string both individually and in relation to each other.