The Tuba is the most powerful organ stop. While some authorities describe this chorus reed as a large-scaled Trumpet, others characterize its tone as being more �closed� than that of the Trumpet. Indeed, Bonavia-Hunt states that some Tubas are close-toned, while others are free-toned in the French manner. The closed-toned variety was developed in England, first introduced in 1825 under the name Ophicleide by William Hill, and later perfected by Henry Willis. The tone of the Tuba depends on a relatively high wind pressure, not merely to produce sheer volume, but to develop the smoothness of tone that characterizes the best examples of this stop. A minimum of 8" to 10" of wind is required, and higher pressures are common. It is constructed in the manner of a large-scale Trumpet, though often with closed shallots. Double-length resonators are often used, even triple-length in the treble (see Harmonic Tuba). It is most commonly found at 8' pitch.
Osiris contains about 130 examples of Tuba (not counting its variants). Nearly three quarters of them are at 8' pitch, one fifth at 16', a handful at 4', and two at 32'.