If you had a tiny set of probes drilled into the bore at various points and measured the air pressure, you would then see these little variations in pressure that develop. . Imagine this: Air from the windway cuts across the labium, some of the pressure rushes into the bore of the instrument, the length of the bore causes the fill time of this to lengthen. The air will reach a peak pressure and then it will depressurize through open tone holes. Also during the depressurization phase, the wind in the windway will be deflected upward and actually create a tiny vacuum that further depletes the bore. You get different notes by opening the toneholes with your fingers, this changes the bore length. Think of this, your playing an "A" on your whistle, 400 Hz. That means that this pressure cycle is occuring 440 times per second. Now, you take it outdoors on a cold day and the instrument plays a bit flat. The temperature will effect the viscosity of the air. When voicing an instrument, you must keep in concern the fact that the air is also pushing out of the bore through the opening near the windway called the "Window". Some designers do not take this in consideration and the result is a weak voiced instrument. ALSO: Note the chamfer in the block, this is critical to good voicing. Here is a simple CPVC close bore whistle that you can build.
Last Update: 1/30/2000