The Structure of the Pipe organ
Pipes made of glued wood lumber
A similar wind system, pipes and mechanical action are all packed into the body of a positive organ. It is known for being able to resonate with a sound rooted in tradition despite its compact size.
Its cuboid pillars are wooden pipes. They are made by gluing together four pieces of spruce wood lumber, which vibrates readily and produces an ideal sound. The material is the same as the expensive board used for the soundboards of pianos.
Varying the lead ratio for different timbres
On the surfaces of the metal-colored pipes are fine patterns. This is because before being cast into a tubular shape, the surface of the plate metal is beaten. By being beaten and forged the welds between component parts are strengthened, and become able to produce a bright, strong sound. Depending on the pipe, some are not beaten.
The metals used are alloys of tin and lead, in ratios that vary according to the timbre sought such as 52% tin to 48% lead, or 70% tin to 30% lead. The former is for pipes of the flute group (a gentle sound), while the latter provides the sound of the principal group (resonating strongly, and characteristic of the pipe organ). Increasing the ratio of lead makes the material harder, and the sound brighter.
The sound of the principal group performs a central role, serving as the fundamental resounding voice within the strong, reverberating sounds of the organ. The pipes that can be seen at concert halls and churches are the pipes of the principal group, and their sound also forms the chorus.
The "mouthpiece" - Recorder-like flue pipes
The materials used to make the pipes of a pipe organ are important, but the shape of the mouth of the pipe is also similarly important. When considering the shape of the mouth of a pipe, there are two types; the large flue pipe and the reed pipe.
Flue pipes have a structure that is similar to a recorder. Wind that has entered from below passes through a slit and forms a sheet-like flow, and on hitting the upper part of the mouthpiece then alternates between flowing into and out of the pipe. With this periodic motion the wind within the whole pipe resonates, and sound is produced. A thick pipe produces a flute timbre, while a thin pipe produces a timbre close to that of a stringed instrument.
Inside a pipe organ the wind flows from below, so the "mouthpiece" is at the bottom, but if turned upside down it is exactly like a recorder. If someone were to breathe into it, a tooting sound would be produced.
When shaving below the mouthpiece of a wooden flue pipe, the square board cover is removed and the part referred to as the block is shaved slightly. This is the route through which the wind will pass from below. This precise shaving can potentially destroy the instrument, or bring it to life.
Excessive shaving cannot be undone, so performing this task comes with a significant responsibility.
Also, irrespective of the raw materials, the angle of the mouthpiece is also extremely important.
The "mouthpiece" - Reed pipes and their appealing, varied timbres
Another variety of mouthpiece form is that of the reed pipe. Reed pipes are structures in which the flow of wind causes a reed to vibrate, causing the whole pipe to resonate and produce sound. By varying the thickness and shape of the reed and the form of the pipe, the timbre can be transformed from the brilliant sound of a brass instrument to the subdued, gentle sound of a bassoon.
The reed is not straight but slightly curved. For this reason there is a small space between the reed and the shallot through which wind passes. As the wind passes, the reed is caught by the air and tries to close. But due to its own curvature, the small space redevelops between the "closed" reed and the shallot. In this way, the oscillation of opening and closing repeats.
The oscillation of the reed when hit by the air forms what is referred to on a synthesizer as a pulse wave, generating rich harmonics. If the resonator, to which the reed is attached at its tip, is a conical tube, this rich harmonic can be exploited. The length and the shape of the resonator can be varied to achieve distinctive timbres.
In this way it is possible to produce a variety of timbres depending on the characteristics of the reed pipe.