The leader pipe is generally considered as about the first eight inches of the tubing of a trumpet onto which is placed the mouthpiece receiver and the mouthpiece. For the other brasses the length would be proportionately different. The mouthpiece receiver is that small section of tubing at the end of the leader pipe which holds the mouthpiece. Functionally, one should consider the leader pipe as starting at the throat of the mouthpiece (see A in Fig. 1) where the diameter is about 0.144 inch. The pipe then tapers to about 0.340 inch, and finally after eight inches the diameter is about 0.460 inch. Only too often both manufacturers and brass teachers do not give enough consideration to this very important portion of every brass wind instrument.
The ideal leader pipe is one in which the tubing is perfectly smooth from the throat of the mouthpiece thru [sic] the pipe, as shown in Fig. 3. Notice how the inside of the the tubing progresses without interruption from the mouthpiece to the leader pipe. In contrast, notice Figs. 1 and 2. This is the way most mouthpieces fit into the mouthpiece receiver.
Fig. 1 shows a most undesirable gap between the mouthpiece and the beginning of the leader pipe; the two simply do not meet. Fig. 2 shows the two meeting, but the inside diameters of the mouthpiece at that point is considerably smaller than that of the leader pipe, producing a difference of .125 inch at a most crucial point on the instrument.
The importance of these differences, even tho [sic] they appear to be small, should not be minimized. Anything less than a perfectly smooth continuation, as in Fig. 3, is to be deplored. A majority of the problems of intonation and tone control can be attributed directly to the leader pipe.
In this discussion we must assume, of course, that the remainder of the instrument is good, having normal proportions, and that the backbore of the mouthpiece is also correctly proportioned. That being the case, we may assume that the fullest tone but the with the poorest control, would be achieved with an instrument that starts with a full bore (same as the bore of the valves) at the beginning of the leader pipe, as shown in Fig. 2, where the diameter of the leader pipe is 0.460 throughout its length.
On the other hand, the smallest tone, but which is most easily controlled, has a leader pipe with starts with an inside diameter (I.D.) equal to that of the mouthpiece backbore and continues with an even tapering as shown in Fig. 4. However, the best control and tone is shown in Fig. 3 where the taper of the leader pipe is proportioned over a greater length of pipe.
From an acoustical standpoint the taper should coincide with the pattern of the nodal lines. A node is point of a vibrating body or system of vibrating particles where there is no movement. For a visible demonstration: take a piece of metal or glass and cover it lightly with sand or sawdust; draw a violin or cello bow over the edge to vibrate the particles. They will arrange themselves to show you where the minimum of vibration is–the nodal points.
The nodal lines of a given tone form perfect geometrical patterns and if these patterns of many individual tones are superimposed and combined, we will have a master pattern which we can use for determining the best shape of the leader pipe–eliminating most of the intonation problems of the instrument.
In a previous article (Nov. 52) I made the statement that intonation and other problems could be helped considerably with just changing the mouthpiece. Consider, however, how much more can be done if we have the entire eight to twelve inches of the leader pipe to work with instead of just an inch or two of the mouthpiece. Interesting in this respect is the fact that one of our leading manufacturers produced an excellent cornet with a leader pipe of eighteen to twenty inches long with the tuning slide located after the valves. However, this instrument was never produced in quantity because so many thought that it did not look right unless the tuning mechanism preceded the valves.
Another variation from the usual is to taper the curve of the tuning slide as shown in Fig. 5. The excellent results from these instruments, mostly foreign made, is due to m longer tapered leader pipe which permits more adjustments to favor the nodal points. Notice in this figure that the straight leader pipe diameter terminates at 0.410 inch allowing .050 inch expansion over the next six inches of the curve of the tuning slide.
The careful study of mouthpieces and leader pipes is highly recommended to the serious student and teacher of brasses. Tho [sic] the present article deals primarily with the trumpet, these considerations apply equally to all brass wind instruments. One might ask, what causes the major shortcomings as illustrated in Fig. 1? There are three answers: (1) the varying inside diameter of leader pipes; (2) the varying outside diameters of the shanks of the mouthpieces; and (3) the varying tapers of mouthpiece shanks among manufacturers. Uniform standards should be adopted by the industry and adhered to as that it is possible to produce the smooth continuous pipe from the mouthpiece thru the leader pipe as illustrated in Fig. 3. In an ensuing article we will point you; several additional improvements and need standardization pertaining to the valves of instruments.