Structure of a Harmonica

• The unique sound of a harmonica, also called mouth harp or mouth organ, comes from its interior design, which is a series of plates. Directly inside each of the outer covers is a thin metal plate of reeds, the top one called the blow reeds since they sound when air is blown into the harmonica, and the bottom plate called the draw reeds because they sounds when air is drawn in through the harmonica. The reeds themselves do not produce notes through their vibration, rather they change the shape and size of the air passageway such that a note is produced. On each plate are slots of different length on which reeds of increasing size are attached at one end. Between the two reed plates is a thicker comb made of plastic, metal or wood, and which contains the actual chambers through which air passes into and out of the instrument and past the reeds.
  
  

Diatonic Harmonicas

• Diatonic refers to the intervals between the notes of the white keys on a piano. In other words, a piano is laid out such that the white keys represent a diatonic scale. Similarly, a diatonic harmonica is designed so the blow reeds in succession produce the three notes of a major chords in a diatonic scale and the draw reeds produce the other notes in the scale according to the diatonic interval. The most common diatonic harmonica is in the key of C major, with the blow reeds producing the C, E, and G notes of a C chord and the draw reeds producing the D, B, F and A notes. Harps in other keys will start at a different note, but the intervals between each blow and draw hole will be the same. Diatonic harmonicas are distinct from chromatic harmonicas, which have a slide that alters the reeds to produce notes not in a normal diatonic interval.
  
  

Playing the Harmonica

• Playing the harmonica consists of blowing and drawing air into the comb and across the plates of reeds, but advanced players know that the shape of the throat, the movement of the tongue, and the pressure and angle at which breathe is applied all influence the quality of the notes. Furthermore, skilled harmonica players can achieve non-diatonic notes even on a diatonic harp by producing what are called overblow bends. Most of the reeds on a diatonic harmonica, both blow and draw, will produce a second, slightly higher note if enough pressure is applied to extend the reed beyond its normal range of movement. Though the harmonica is relatively simple by design, the extent to which the actions of the performer influence the resulting sounds makes playing it a very personal experience.