colors. This allows reed stops to imitate historical musical instruments, such as the krumhorn or the regal. Because the resonator is partially stopped/closed by the reed, odd-numbered partials/harmonics are dominant (in the hollow tones of Krumhorn and Clarinet stops, for example). If the resonator pipe expands outward to conical, the geometry allows the production of both even- and odd-numbered partials, resulting in the fuller tones of Trumpet and Oboe stops. Free reed pipes These are quite uncommon; see "Free reeds" in the "Reed pipe" article. Diaphone pipes The diaphone is a unique organ pipe. Uncommon in church and concert pipe organs, they are quite common in Theatre Organs. Invented by Robert Hope-Jones around 1900, it has characteristics of both flue pipes and reed pipes. The pipe speaks through a resonator, much like a reed pipe, but a spring-loaded pallet instigates the vibration instead of a reed. Possessing a powerful bass groundtone, the pipe is generally made of wood and can be voiced at various wind pressures. The diaphone is usually found at 16' and 32' pitches, however there are a few examples of 8' diaphones. There are two 32' Diaphones in Philadelphia's Wanamaker Organ, and a full-length 64' Diaphone-Dulzian is installed in the Boardwalk Hall Auditorium Organ in Atlantic City. The Diaphone pipes are used for the bottom 12 or 18 notes of the 16' Diapason rank, and also for its bottom 32' octave, on those few Theatre Organs that go that low. Hope-Jones also developed an imitative version of the diaphone called the diaphonic horn, which had a more reed-like quality than the diaphone and was voiced on lower wind pressures. Wurlitzer built a version of the diaphonic horn for their theater organs at 32' and 16' pitches with huge wooden resonators as extensions of its Diaphonic diapason, and at 16' with metal resonators as an extension of its smaller-scale Open diapason. The Austin Organ Company also developed a metal diaphone at 16' pitch known as a Magnaton. Due to its penetrating tone, a diaphone-type horn has also been used in foghorns and fire signals. See also Tibia (organ pipe) Tone hole References Pipe organ components Musical instrument parts and accessories