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Schematic of a typical reed pipe

A reed pipe (also referred to as a lingual pipe) is a sound-producing component of the pipe organ that is driven by a vibrating brass strip known as a reed.

A reed pipe is comprised of a metal tongue (the reed) which rests against a shallot, in which is carved a tunnel, and is held in place by a wedge, which is made of wood. This assembly protrudes from the underside of the block and hangs down into the boot. A tuning wire is inserted though the boot and is bent to hold the reed against the shallot. The wire is moved up or down in order to change the length of the tongue which is permitted to vibrate, thereby changing the pitch produced by the pipe. The resonator joins with the upper opening of the shallot and extends above the boot. The resonator may be made in a wide variety of lengths, shapes, and configurations, depending on the desired tone quality.

As wind under pressure enters the boot, it travels over the reed, causing it to vibrate against the shallot. The wind passes through the shallot and up into the resonator. The reed tongue itself produces the sound, which is focused and refined when the sound wave passes through the resonator. In addition, the length of the tongue is the most important element in determining the pitch of the sound produced: the resonator of the pipe is tuned to be sympathetic with the vibrating reed, but changes to the length of the resonator have a greater effect on the pipe's tone quality than on the pitch.

In the nineteenth century, some organ builders used a type of reed construction known as free reeds in some stops. The term refers to the fact that the tongues for each pipe are not enclosed in their own boot, as in standard reed pipes, rather all the tongues are held together in the same chamber, much like in a harmonica or an accordion. Because of this arrangement, true volume adjustments are possible through variations in wind pressure.

The most important element of a reed pipe with respect to determining its final color is the interaction between the shallot and the tongue. Whether the shallot is cylindrical or tapered (and, in the last case, whether the taper is inverted) greatly affects the pipe's timbre. Likewise, the "cut" (referring to the depth of the shallot and the shape of the opening) and the closed-end shape (whether the closed end of the shallot is flat, domed, or Schiffschen) determine whether the tone is more Baroque or more Romantic. Because the movement of the tongue instigates the vibration, it is of primary importance in controlling the tone of the pipe. The metal alloy used, the alloy's hardness, and the tongue's thickness play an important role. The reed voicer's greatest tool is in controlling the curve of the tongue, because this controls how the tongue beats against the shallot. Also, the type of block (standard or French "double-block") in which the reed assembly is set has an effect on the sound.

Scaling is important when determining the final tone color of a reed pipe, though it is not of primary importance as it is in flue pipe construction. This is because reed pipe resonators simply reinforce certain partials in the tone; the air column inside the resonator is not the primary vibrator. Likewise, the material out of which the resonator is constructed does not matter as much as with flue pipes. The shape of the resonator, however, is quite important: an inverted-conical resonator (such as is typical with a Trumpet rank) produces more harmonics than does a cylindrical resonator (like that of a Clarinet).