Reed Pipes
In reed pipes, a thin strip of brass, called the "reed". is set in motion by a flow of air past it, and its resulting vibration is given tonal character by the top part of the pipe, known as the "resonator".
A simple experiment will demonstrate how a reed pipe works. Take a fairly thick blade of grass, and hold it taut between your thumbs, holding your hands out, palms together. Blow fairly hard between your thumbs, across the grass, and a loud squawk will be emitted. Then try cupping and opening your fingers as you blow, and the "tone" of the squawk will change. You have made a very simple model of a reed pipe. The grass is the reed, which vibrates as air passes across it, and your fingers and hands act as a resonator.
Organ pipes are far more sophisticated, but they work in the same way. The brass reed is held tightly in place by a small wooden wedge against a brass tube with a slot in the side adjacent to the reed. this tube is called a "shallot". Wind passes into the foot of the pipe, called the "boot", and is forced through the shallot past the reed, causing the latter to vibrate and generate a sound similar to the squawk from the blade of grass. The pipe's resonator controls and determines the tonal character of the sound emitted.
The resonators of reed pipes vary immensely in shape and size, depending upon the tone quality desired. They are often of short length, and although a pipe sounding eight foot pitch may have a resonator which is eight feet long (as in a Tuba Horn), in many other ranks, the resonator may be very much shorter. The extreme example is the Kinura, where the pipe sounding bottom C of eight foot pitch has a resonator only an inch or so long. The illustrations in this book show the shapes of resonator used in Australian theatre organs to produce different types of tone-colour. In Style 260 organs, the Trumpet and Saxophone pipes have resonators made of polished spun brass, with flared "bells", and make a truly impressive array. Reed ranks can easily be identified at the console, as the stopkeys controlling them are usually coloured red.