Diapason

Diapason (Gk.), 1. Fr.: pitch pipe; tuning fork; scale; 2. organ stop of cylindrical metal flue pipes of wide scale at 8' pitch, the foundation of Amer. and Brit. organs, equivalent to the Fr. montre and Ger. Prinzipal. When it occurs at 4' pitch in the manual, it is called *octave. The diapason is nonimitative in tone and has been in existence since the 16th c. See also: open diapason, stopped diapason (129). Lewis, Walter, and Lewis, Thomas. Modern Organ Building. London, 1939.