Pipework

What however, is the most significant feature of organ tone of this period is the high degree of craftsmanship embodied in voicing of individual and ensemble ranks. This craftsmanship gave the organ a dignity and grandeur which places the work of the master builders of this time in the annals of organ-building history.

Although what follows is a technical account of tonal production methods, this is not the secret of the art of these men. Their results came from skill of the highest order and what they accomplished cannot be gained from any paper account but only by practical listening experiment.

The greater number of pipes in the instrument of this period are flue pipes. A flue pipe consists of a foothole which takes wind under pressure from the wind-chest; the foot itself in which the wind builds up pressure; the languid which separates the foot from the body except for a narrow slit called the flue, through which the wind passes; the mouth which consists of upper and lower lips flanked by the "ears"; and the body or "speaking" length in which the sound waves are set in motion.

The factors determining the quality of tone to be produced are wind pressure; diameter in proportion to length; shape; width of mouth; height of mouth; depth and numbers of "nicks"; and material.

The wind pressure depends on firstly, the pressure from the bellows (which in the case of the instruments to be discussed would be 2 ½ to 3 ½ lb per square inch) and secondly, bore of the foothole where the wind loses pressure by friction the more the foothole becomes restricted. The process of adjusting the wind pressure in the pipe is known as "regulating".

The diameter in proportion to the length of the pipe gives the "scaling". This is taken at the lowest note, the inside measurement being the one taken. The scaling of organ pipes depends on the size and acoustical qualities of a building, while the proportions of each organ pipe in a set cannot be maintained throughout the compass, i.e. although a pipe an octave above another is half its length, the other proportions, diameter and volume of air in the tube is not proportional.

The mouth of a pipe is said to bear some proportion to the circumference of the pipe, e.g. a pipe may have a "1/3 rd" mouth. The "cut-up",, the distance from the top of the bottom lip to the edge of the top lip is made proportional to the width of the mouth. As the out is made higher, so is there an increase in power. When the cut-up is low a string tone results; when medium, diapason tone is produced and when high, flute tone is produced. Thus it will be seen that the cut-up effects the harmonic development of the note, giving it its particular tone quality. Especially important in the harmonic development the note is the shape of the upper lip which may be modified within certain limits, a blunt, thick lip curtailing the harmonics while a sharp, thin edge encourages them. Between these two extremes there are many variants of "edge formation" (with or without the bevelling of the upper lip) which modifies the tone in the subtlest manner.

To explain this. it should be remembered that it is here the secondary vortex (or sound eddy) forms combining with the primary vortex formed at the flue to produce a periodic vibration of the wind-stream at the mouth of the pipe from back to front, It is thus that the vortex system with its own fundamental note and harmonies acts as the originator of the sound produced by the pipe as a whole. This system operates given three aerial conditions; the outside stagnant air, the inside stagnant air and the air stream flowing from the flue. Two sets of vortices are generated at the flue, one set hitting the upper lip, the other set missing it. Hence the necessity for the condition of the outside stagnant air. It is the function of the vortices in this conditioned environment that produces edge tone.

These vortices set in oscillation the air stream in the mouth about midway between the two lips which in turn sets in motion the air column in the 'body of the pipe which in turn starts vibrating longitudinally. The air column now becomes the greater influence in the partnership, profoundly affecting the mouth tone. It is the relationship between the vortices or edge tone and the body of air in the tube or column tone that makes the flue pipe a "coupled" system and it is the fact that the pitch of the edge tone can be made to rise or fall to that of the column tone which makes the treatment of the upper lip so important.

The "ears" which are not required for the very small high-pitched pipes provide some measure of protection from the outside air and help to restore the balance of pressure to some extent. Their addition lowers the pitch of the note slightly.

The "nicks" are V-shaped impressions made in the bottom lip and languid to steady tone and to elimate a snarling tone generally undesirable. Diapasons and pipes with few overtones require to be sparsely yet deeply nicked; oppositely, gambas and small-scale work generally require to be nicked closely and with faint impressions in proportion to the extent it is desired to retain the keenness, in effect of tone, of the untreated edge, so that in many cases the nicking has the appearance of microscopic saw teeth forming a continuous serrated edge.

Wood pipes may be nicked on the block alone or on the cap, or both. Wood basses are generally nicked on the block alone while large-scale 16' basses are left unnicked.

The reed pipe, like the flue pipe is a "coupled" system between the vibrations of the reed and those of the air column in the tube. Either of them can be made to control the other within certain limits; for instance, the pipe may be sharpened in pitch by shortening the vibrating length of the tongue or by shortening the effective length of the tube. There is a certain degree of material control of the reed and tube, but this cannot be pushed too far as the pitch will change suddenly.

The tongue of the reed which is made from brass is curved, this curve varying from parabolic to logarithmic in shape. This shape is important to the tone, enabling, the tongue to cover and uncover the shallot by a rolling and unrolling process.

There are three main types of shallot; the open shallot, the closed shallot and the filled-in shallot. The first gives a loud tone, rich in harmonies; the second, a popular type. gives a brilliant tone when used with small-scaled tubes and high wind pressures while the third is used for producing tromba, horn or other smooth reed tone.

The type of tone is also influenced by the nature of the metal used in making the various parts of the reed. The boot and block should be heavily made and the reed tubes should be made of an alloy rich in tin. A certain reinforcement is desirable where the tube fits into the block, and in order that there shall be a proper transformation of the energy of the wind which passes the reed, the tubes should have a critical bore at the top.

Various types of stops.

By acoustic theory, a conical tube reinforces the harmonics in their natural series. Thus conical tubes are used for pipes of trumpet tone, the power varying to a certain extent with the width of the tube. Wooden tubes can be used and zinc is often used for the largest pipes. The swell oboe may be made with a "close" tone. The tube consists of a narrow cone surmounted by a conical bell which is partially covered at the top by soldering on a regulating cap or shade. Opening the cap gives a brighter tone while closing the cap makes the tone smoother but weaker.

The orchestral oboe has a thin cylindrical tube with a bell and the opening of the shallot is very narrow. If a "double bell" is fitted to an orchestral oboe type of reed, its tone becomes that of a cor anglais.

The clarinet type of stop has cylindrical tubes which reinforce the odd-numbered harmonics only. The tube is half-length and capped while an extremely thin tube gives musette tone.

The vox humana is a type of clarinet with a short tube usually of one-eight length.

Before leaving the question of tonal production mention should be made of two types of flue pipe not already discussed. These are the harmonic pipe and the stopped pipe. The former is a pipe double the required length and pierced not quite half-way down so as to sound the first harmonic. It usually has a very sweet tone.

The latter consists of a pipe with a stopper at the top and only half the necessary length. This is explained acoustically by the fact that the node is now at the end of the pipe instead of at the centre as in the case of open pipes.

Finally, mention should be made of the effect of a building upon the tone of an instrument. The acoustic properties of a building can very often be the best "voicer" an instrument can have. Curved ceilings which diffuse the sound can greatly enhance the tone of an organ by creating considerable reverberation period, though this can have its extremes too, thus be-coming a disadvantage instead of an asset.