Wild Air

A pipemaker working with the metal plane.

When we last checked in on the pipe craftsmen in the Czech Republic, they had poured sheets of hot liquid metal onto a long table to cast the material for the new organ pipes for the Shelbyville organ.

Then, we had to wait. Even in our busy, hi-tech world, some things take patience. If we want bread to taste good, we have to wait for it to rise. In the case of our pipe metal, we had to wait for it to cure before anything more could be done with it. Organ pipes made of “green” metal are never satisfactory. The curing process usually takes about 6 – 8 weeks.

When unrolled, the new metal has a shiny, spotted surface, which was on top on the casting table, and a dull surface on the bottom where the sheet was in contact with the fabric top of the table. To assure uniform metal thickness, and to provide a smooth surface on the interior of the pipe, the metal must now be planed.

This is one of the few steps in the pipemaking process where modern technology makes things much easier. At one time, if the pipemaker needed to have his metal planed, he had to plain it by hand. Mechanization can, indeed come to the aid of art!

The pipemakers mount the sheets, shiny side down, on the drum of the large machine. As the drum rotates, a small amount of metal is removed until the sheet is level. The machine is essentially a very large lathe.

When the Shelbyville organ was built, some of the more powerful ranks, such as the Diapason Major, were built “fabric-side out.” These pipes, which were made of common metal (mostly lead), had thick walls, with the smooth “top side” of the lead sheet to the inside of the pipe. In some cases, the upper lips of the pipes were covered with leather to allow the pipes to have a very smooth, powerful sound under high wind pressure.

Whenever you see a pipe with the fabric marks still visible, you can be sure that that pipe maker wanted the warm components of the tone to be preserved and emphasized. Usually, fabric-side-out pipes are used for dark, powerful sounds. To understand why, we have to look at how the pipe produces its sound, and how that sound is reinforced or amplified.

Functionally, there are two major components to an organ pipe. First, there must be an oscillating mechanism – what in a loudspeaker would be called a “driver.” In a pipe, this can be either a flue or a reed. More about reeds later…

In a flue pipe, a narrow sheet of air blows from the flue (the narrow slit at the bottom of the mouth) across the upper lip. The wind sheet oscillates because, as the old saying goes, “nature abhors a vacuum.” The windsheet oscillates because it can’t decide if it wants to deflect inward or outward. Whichever way it blows, it creates a vacuum on the opposite side, pulling the sheet in that direction. A tone is created because, essentially, the wind sheet can’t make up its mind!

This oscillation sets in motion the second major component of the pipe, the air column or resonator. The length of the air column in a pipe determines its pitch. The width, as contained by the sidewalls of the pipes, controls which harmonics in the musical note are emphasized.

Louder pipes, and pipes with stronger lower frequencies are made of heavier metal to contain the movement of the air column inside, which can become very energetic. It takes stout walls to contain this vibrating air column without canceling any of it.

Try this simple test.

The next time you are in a room with a powerful sound source, place your had flat on the wall. Do you feel vibration? If you do, the wall is canceling out some of the sound. It takes energy to vibrate that wall, and that energy is absorbed from the sound waves. Likewise, if the tone of an organ pipe is powerful enough to cause the wall of the pipe to vibrate, that vibration is cancelling out some components of the sound. In fact, in the case of string pipes, for instance, the metal is intentionally thin, so the upper harmonics are stressed.

A sad problem that we encounter from time to time is a pipe that stops speaking when you try to tune it. Just touching the tool to the top of the pipe seems to cancel its sound. This happens because the wall of the pipe isn’t thick enough to contain the sound wave. The vibration in the pipe body cancels the sound wave so powerfully that any disturbance makes the pipe stop speaking. Wrapping your hand around such a pipe (which, by the way are NEVER found in Reynolds organs) in the right place will stop the vibration in the metal, and the pipe will begin speaking again.

This brings us to one of the reasons a pipe organ sounds so good in a room like St. Joseph’s. The building was built to last, with thick, tall masonry walls that reflect sound efficiently.

So, now that are metal has cured, and has been machined to a uniform smoothness and thickness, it’s time to make some pipes!

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