TOOT SWEET
Utilitarian shop whistles and elegant organ pipes
have a lot in common.
Basically, a whistle works by splitting a column
of fast-moving air with a narrow blade. Doing so
creates turbulence that in turn causes the moving air column to vibrate. A resonant chamber or
“bell” placed above the blade allows the whistle to
be tuned to a particular frequency or pitch, while
simultaneously increasing the wave amplitude
(sound volume).
The layout and tolerances of a whistle are exacting. The difference of only a few thousandths of an
inch in any of the components (see facing page)
can mean the difference between a pure, loud
whistle tone and a mushy hiss of chaotic air.
I wanted to outfit my new workshop with a loud,
well-tuned compressed-air whistle. When noon rolls
around, there’s nothing more satisfying than pulling
a cord to sound a long, sustained honk before heading in for lunch. My first few attempts at whistle
making were mediocre at best, resulting in devices
that did little more than hiss and chuff, emptying
my air compressor’s tank faster than three Green
Bay Packers fans sharing a can of lager.
Frustrated, I turned to Timothy Patterson of
Patterson Organworks ( pipeorgan.us) in St. Paul,
Minn. He’s a master organ builder and a man
with an unsurpassed understanding of vibrating
columns of air. Patterson has worked on organs
around the world, from a 400-year-old organ in
Normandy to the latest computer-controlled
models in the United States.
Photograph by William Gurstelle
In Patterson’s modest shop stands a nearly
completed 15-rank, 33-stop pipe organ (shown
here). The organ pipes, up to 16 feet long, share the
same operating principles as my contemplated air
whistle. Clearly, if anybody could get my whistle to
sound properly, it is he.
Patterson and I sketched out several ideas, finally
developing a design for a robust air whistle capable
of producing a rock-concert-like 118 decibels at
a distance of 6 feet, using a standard home air
compressor.
Even better, the lengths and diameters of the two
resonators specified produce a strident,
attention-demanding sound: the wonderfully
dissonant interval known as the tritone. (For
non-music majors, the tritone is the musical
interval that spans three whole tones. Musicians
would recognize the sound as an augmented
fourth. Commonly employed to produce musical
discordance, the tritone is well suited for
a signaling whistle.)
In medieval times the tritone was called diabolus
in musica, or more simply “The Devil’s Interval.”
The sound of the tritone was so dissonant that
it was banned from church music. In fact, some
church officials of the Middle Ages believed that
simply hearing the interval would stir up sexual
desires in the listener. Thus, churchmen said the
tritone was the sound of Satan.
The Super Tritone Shop Whistle does not seem
particularly diabolical until the time comes to tune
it properly. But once completed and tuned, the
Super Tritone sounds with a mighty blast, letting
the neighborhood know it’s lunchtime, quitting
time, or simply time to blow the whistle.
To hear the Super Tritone Shop Whistle,
visit makezine.com/12/whistle.
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