Acoustical and physical dynamics of the diatonic harmonica.

The harmonica is arguably the most widely played instrument in the world, yet there is a surprising paucity of published studies of its acoustics or physical dynamics. The typical diatonic harmonica and the physical forces involved in its natural function are described, and simple observations of the harp's functions are reported. The speaking of the reeds, naturally, when producing a bend, and when speaking as an overblow or overdraw is discussed and investigated by simple stopping of the reeds, by videostroboscopic analysis, and by recording vibration of the reeds with displacement gauges. The reeds of the ten hole harmonica can be made to vibrate at varying frequencies depending on the size and shape of the player's vocal tract. Three different modes of speaking from each hole and its pair of reeds are revealed and studied: first, naturally in a closing mode, either blown or drawn; second, as a bend, either blown or drawn, with pitch in the interval between the two notes in the hole; and third, as an overblow or overdraw in an opening mode with a pitch outside the interval between the two natural notes of the hole. This dynamic interaction allows the player to speak with the instrument perhaps as with no other.