The general design used here is not my own, as I have relied on many sources from the internet and elsewhere. This is just my particular implementation of this simple whistle design. I have included more detail on the construction and performance from my own experience in building it. I have also included some optional features of my design, such as an attachement for use with an air compressor, and a moveable slide that allows the pitch can be changed.
By adjusting the length from the opening to end of the pipe, the pitch can be increased or decreased. The pitch produced depends on the speed of sound and the length of the whistle from the notch to the capped end.
The pitch, in Hertz (Hz), can be calculated as:
Pitch = [Speed of sound (in ft/second)] / [ 4 X Length of wistle (in inches) / 12 ]
The length of the whistle corresponds to 1/4" the wavelength of the sound produced.
The speed of sound is approximately 1100 feet per second.
Qty (1) 1" PVC end cap
Qty (1) Length of PVC pipe. The exact length is determined by the desired pitch. About 10" is a good length to start with.
Qty (1) 1" PVC coupler
Qty (1) 1" to 1/2" PVC adapter
Qty (1) 2" length of 1/2" PVC pipe
Qty (1) Length of 1" diameter wooden dowel or other round stock that will fit tightly into 1" PVC pipe
Step 1: Cutting the Notch
Two cuts must be made into the PVC pipe to make a notch, as shown. The first cut is perpendicular to the axis of the pipe. The second is at a 45 degree angle. Make the first cut about 1" to 1.5" from the end of the pipe, as shown.
Step 2: Making the Insert
The insert fits into the end of the pipe with the notch. It can be made from a wooden dowel or any other round stock. I made this one out of a hardwood dowel.
One side of the dowel must be removed as shown in the pictures below. Cut the dowel so that the flat is about 1/4" from the edge as shown in the diagram.
The insert should fit fairly tightly into the PVC pipe. Push the insert into the pipe so that one end of it is even with the perpenicular cut of the notch in the pipe.
Refer to the note included with the pictures below for additional construction details.
Step 3: Making the Mouthpiece
Step 4: Optional Air Compressor Attachment
The construction is very similar to that of the regular mouthpiece. The only difference is that a 1/2" PVC plug is used in place of the 2" section of 1/2" PVC pipe. I then drilled a hole in the 1/2" plug, and tapped 1/4" NPT pipe threads into the hole, so that I could screw in the quick coupler attachment (the metal piece shown).
Step 5: Optional Adjustable Stop for Chaning the Pitch
You can make an adjustable pitch whistle by makeing a plunger that slides in and out of the tube, effectively changing the inside dimensions that determine the fundamental pitch.
The plunger must fit tightly enough that air doesn't escape past it, yet loose enought that it can be moved in and out without appling excessive force.
I make the plunger out of a 1/2" PVC end cap. The end cap will not fit down the 1" PVC pipe off the shelf, so the end cap will have to modified. I used a lathe to turn down the diameter of the cap until it fit well. If you do not have a lathe, a belt sander could be used but it would be less precise and also it would be difficult to keep a round shape that would seal well in the pipe.
The plunger could be made of any solid material, like a wooden dowel, so long as it has a good fit as described earlier.
Step 6: Performance
The graph below is the spectrum of the sound produced by the whistle. You can see the fundamental frequency, the first spike, is approximately 350 Hz. You can also see that there are odd numbered harmonics. The third harmonic is at approximately 1050Hz, and the fifth harmonic is at approximately 1750 Hz.
Recall that the length of the whistle corresponds to 1/4 the wavelength of the sound produced, and that the speed of sound is approximately 1100 feet per second. Therefore, a 9.5" whistle should produce a sound with a fundamental frequency of approximately 347Hz. This calculated result agrees well with the frequency on the graph below.
I've attached a wave file of the sound produced by this whistle.