Related Field: Pipe Organ Voicing

Perhaps the oldest work in aerodynamics—the study of moving air—can be found in an unexpected place. Long before wind tunnels and airfoils, before the Wright brothers and powered flight, airships and streamlined automobiles, pipe organ voicers figured out how to manipulate airflow to create a wide variety of sounds.

Detail of the Zliten mosaic (2nd century CE), depicting the playing of several instruments including a hydraulis, the predecessor of the modern pipe organ. (image credit: Wikimedia Commons)

A Brief History
 
The roots of modern organs trace back to ancient Greece, where an engineer named Ctesibius invented a water-powered organ around 246 BCE called the hydraulis. This instrument disappeared from western Europe after the fall of Rome but evolved into the pipe organ in the Eastern Empire and was reintroduced around 800 CE. Since then, organs have underpinned Western music; the instrument shares its name, organum ("instrument" or "tool"), with the first polyphony and grew as an accompanimental and solo instrument along with the development of European music. The organ building industry still thrives today, with several fine builders operating in the US and Europe.

Paul Fritts & Co. builds historically-inspired mechanical action organs like this one, in Lagerquist Hall at Pacific Lutheran University, Tacoma, WA.

What Does This Have to Do with Aerodynamics?
 
Musical instruments using air movement to create sound predate the pipe organ by a long time—tens of thousands of years, in fact. The earliest flutes, some 30,000-40,000 years old, were made out of bone, and when the hydraulis was invented it produced sound in essentially the same way: air blown through a tube moves past an open slot where it fluctuates in and out of the body of the instrument, creating a regular vibration which we hear as a tone. By the time the organ was re-introduced to Italy in the Middle Ages, these pipes had evolved. A flat plate called a languid now blocks off most of the air and forms a slot or flue at the front of the pipe where a sheet of air is blown out and past an upper lip. Moving the front of the languid up or down changes the angle of the windsheet, causing the pipe to speak or not. The art of voicing an organ pipe—for the last thousand years or more—is really the science of manipulating airflow to produce a desired result.

Pipe mouths, showing the languid sitting behind the flue and lower lip. The pipe in the center of the point is embossed—the pipe metal is scored on the backside before it is rolled up, leaving a visible pattern.

Some of the tools of the organ voicer and car aerodynamicist are the same. For example, turbulence in the windsheet greatly affects both the speech of the pipe and its tone color, and voicers discovered as early as the middle of the 18^th century that nicking the front edge of the languid could reduce this turbulence and improve the speech—but at the expense of “deadening” the tone by suppressing some of the upper harmonics. Similar to vortex generators on cars, which are used to reattach flow or eliminate troublesome wind noise, the nicks help get rid of unwanted turbulence, fluctuations, or frequencies in the air stream.

These pipes date from the 18^th century; the nicking (visible just below the flue) was likely added at a later date. The VG on the right is on a 2018+ Toyota Camry, between the mirror and front window. This is a common location to find VGs on cars.

The fascinating thing about pipe voicing is that most of the tricks and methods that have been developed over the centuries to manipulate the airflow through pipes were done by trial and error, long before any sort of aerodynamic theory had been discovered. Other techniques voicers use to get the right sound include altering cutup height (how far the windsheet travels before it hits the upper lip), skiving the upper lip (cutting it at an angle so it terminates at a sharp edge rather than a blunt one), bowing or flattening the upper lip, pushing or pulling the lower lip to narrow or widen the flue, knocking the languid up or down to change the angle of the windsheet, and carving material or burs out of the sides of the mouth (the opening on the front of the pipe, between the upper and lower lips), which can reduce turbulence and/or widen the windsheet. All these actions have to be balanced; changing one parameter affects many others, as is true in automotive aerodynamics too.
 
Additionally, the size of the toe hole which admits air into the pipe, the pipe material and wall thickness, how that material was cast, the pipe’s shape, its mouth width, its diameter or scale, the wind pressure and design of the reservoir on which the pipes sit, and the key action type (electric, pneumatic, or mechanical) all affect the sound. So you can see that quite a lot of parameters have to be considered when designing and then voicing an organ! Voicers must be technically skilled, have an excellent ear, have a good sense of artistry, and be able to voice thousands of pipes in a single instrument to an exacting degree. This helps explain why there are so few of us who can do it.

It's not always "all work and no play" though.

Here I am playing the dedication recital for an organ I helped build in Latrobe, PA. I voiced about half of this instrument, around 1,500 pipes or so:

(Alleluyas, Simon Preston [b. 1938])