Reed pipe
An organ pipe with a reed.
What it means
With a reed pipe, the tone does not arise at a cutting edge but through a vibrating metal blade. The reed lies on a shallot and is set in motion by the wind; it periodically interrupts the airstream, and the attached resonator shapes the sound. A tuning wire or crook fixes which part of the reed vibrates freely, and thereby determines the pitch. The second large group of organ pipes are the flue pipes, in which the air is broken at an edge.
Musical use
Reed stops supply the most powerful and sharpest colours of the organ: trumpets, trombones, and shawms give the full organ brilliance and carrying power, while quiet reed voices serve as characteristic solo colours. In the French organ tradition they form a group of their own, named as such, on which whole types of writing rest. Because their sound is rich in overtones, it blends less than that of flutes and principals; it is therefore used deliberately, either as a solo or as a crown over a carrying foundation. Their sensitivity to temperature is greater than that of the flue pipes.
Performance practice
Expect reed stops to go out of tune faster than the rest of the organ, especially when the room temperature changes; check them before important performances and have them retuned if necessary. Register them with a sufficient foundation, or they sound bare and obtrusive. Avoid holding many low reed voices together for a long time, because on some instruments this strains the wind supply. Report sticking or howling pipes to the organ builder, stating the stop and note, rather than intervening in the mechanism yourself.
Bear in mind that reed voices respond at a different speed than flue pipes: in fast passages this can lead to an audible offset, which is why a calmer articulation helps there. Check this on the instrument you are playing. With temperature changes, expect rapid detuning and have the reeds retuned before important performances. Register them over a carrying foundation, so the sound does not seem bare, and avoid long-held low reed sounds if the wind system reacts sensitively to them.