The back and sides need to be constructed out of a hard, stiff wood that will not absorb any of the soundboard's vibrations. Each string on a typical guitar has one open string and 19 fretted notes. There are only 44 different pitches. Repeated notes on different strings are called unison pitches. The guitar has an unequal standard tuning system - perfect fourths between each adjacent string pair except the third and second, which are tuned to a major third.
Guitarists frequently use unison pitches to tune the guitar.
In a system called relative tuning, the pitch of the open fifth string is matched to the fifth fret of the sixth string. This procedure is duplicated until the third string where the unison for the second string is found on the fourth fret to accommodate the major third. Although unison notes have the same pitch, they have a slightly different sound. Musicians often use words like warm, bright, dark, fat, or thin when talking about timbre. The Vihuela was popular in the 16th century.