Originally Posted by ecox
How 'bout a CD from the old Atlantic City organ -- real 64' pipes, extending down to 8hz. And it could create 128 foot pipes using interference between notes, causing a 4 hz fundamental!
yup. that's called a "resultant" stop
The organ possesses a unique stop in the organ world, the 64' Diaphone-Dulzian in the Right Stage chamber (Pedal Right division), one of only two true 64' stops in the world. (The other 64' stop is the Contra-Trombone reed stop in the Sydney Town Hall Grand Organ.) The stop is unique because it is a reed/flue hybrid.
When construction of the organ commenced, it was planned to have two 64' stops in the pedal, a Diaphone Profunda and a Dulzian. Later, the design was revised, and the Diaphone was cut, because it was feared it would crowd the Right Stage chamber (due to the width of the pipes). Consequently, the Dulzian was moved to the Right Stage chamber. However, the sound of the 64' Dulzian did not meet the criteria, requiring Diaphone pipes to be used for the lowest 22 notes. The remaining pipes in the rank are reeds. Because of the low frequencies involved, and because the diaphone is voiced to imitate a reed stop, the transition from reed to diaphone cannot be heard.
The Diaphone-Dulzian's low-C pipe stands 64' 9" (19.7 m) tall, weighs 3,350 pounds (1,675 kg), and produces a frequency of 8 Hz (the sound of the vibrating pallet is described as "a helicopter hovering over the building"), a tone that is more felt than heard. The pipe stands upright for about 40 feet (12 m), the remainder is mitred (turned) towards the Right Stage chamber's grill. All pipes taller than 32 feet (9.8 m) are designed in this manner.The Diaphone-Dulzian rank spans from C3 to g²; it is sufficiently extended so that the 64', 32', 16', 8' and 4' unison stops, and the 42²/3', 211/3' and 10²/3' mutation stops, may be drawn from the same rank. No other extension rank in the world spans that far. Also, when the 64' and 42²/3' are combined, the resultant tone simulates a 128' stop, equivalent to a 4-Hz tone on low C.
Use of the Diaphone-Dulzian is rare, being used primarily in registrations of moderate volume. It may drowned out if too many registrations are used, and overpowering when dominant. Additionally, extended use of the stop's lower notes may cause structural damage to the building.