Thursday, March 1, 2012

PVC Slide Whistle

The pvc slide whistle is a modification to the pvc steam whistle which allows multiple tones to be produced  by changing the length of the whistle tube with a piston, just like a toy slide whistle.   Here are the additional items you need to turn a pvc steam whistle into a pvc slide whistle. 

•a 1/2'' pvc steam whistle (6-8'' long from the bottom of the whistle mouth)
• a large chop stick
• a 00 size rubber stopper
• 3/8''id, 1/2''od vinyl tubing (about 1/2'' long)
• 1/2'' pvc pipe cap

• a drill with 1/4'' bit (or one at lease the size of you chop stick)
• hot glue gun

To make a piston we took a large chop stick (about 1/4'') and sharpened it in a pencil sharpener, then  poked it into the small end of a 00 size rubber stopper and hot glued it in place, being careful that it was on straight.

To make a perfect seal inside the pipe we put a small piece of 3/8'' id, 1/2'' od vinyl tubing over the stopper.  By test fitting the piston into the pipe and pushing it further onto the stopper to stretch it slightly you can get a really good seal.

To put it all together drill a hole in the center of the pvc cap put the chop stick through and then put the piston in the whistle and the cap on the end to keep it straight and prevent jamming.  Whistles with chambers of 6-8'' seemed to work well for 1/2'' pvc pipe. You will be able to get lower notes with a longer 3/4'' pipe without over blowing.  

Things to do and notice:
Other than being fun to play with and an instrument you can learn to intuitively play melodies on the nature of a slide whistle can show you a lot about how the dimensions of the whistle effect the sound it produces.  The obvious effect is that by lengthening or shortening the whistle by moving the piston you can lower or raise the note it produces. The more interesting information you can glean from a slide whistle is how hard or soft you have to blow to get a natural note without over blowing. We found, as the steam whistle resources suggest, that the further out the piston is the softer you had to blow to avoid an overtone. The only way to avoid this is lower the length to diameter ratio by making the whistle wider. Interestingly enough we also found that if you push the piston in too far (which is not all the way in) the whistle stops sounding and the only way to solve this is to make the whistle narrower. When you think about the sizes of high and low pitched wind instruments, say a fife vs a bassoon, you realize that people  have had this figured out for a long time, but you don't usually see it in one instrument.    

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