Monochord
Instrument with a single string for determining interval ratios.
What it means
The monochord (Greek for "one-stringed") is an instrument with a single stretched string over an elongated resonating box. A movable bridge divides the string into two sections that can be measured and compared. It is not used for making music but for demonstrating and calculating pitch ratios.
Musical use
Tradition attributes its invention to Pythagoras. With the monochord it can be shown that the octave stands in the length ratio 1:2, the fifth in the ratio 2:3 and the fourth in the ratio 3:4. In the music theory of antiquity and the Middle Ages it was the most important teaching and measuring device; it was also used in constructing tunings and dividing the scale. Today multi-stringed instruments that are also called monochords are used in sound therapy.
The monochord should be distinguished from the tromba marina, a one-stringed bowed instrument that was intended for making music.
Performance practice
If you use the monochord in teaching, divide the string with the bridge and listen to the intervals one after another. Take care to pluck the string in the same way at each division so that you can compare the pitches reliably.