Ryan: You’re probably right about the vibrations of the motor being the source of the pitch. The resonance of the tube was my first thought, but I doubt that it actually makes any difference in the pitch. But if you feel like trying an experiment along those lines, let me know how it turns out!

AJ Harbison

One possible cause of the sound could be the vibrations from the motor. If this is the case then the difference in pitch between the two motors would be due to a difference in motor speed. As you know the units for pitch are Herz (or cycles per second). This can be likened to the speed of the motor in units of RPM (revolutions per minute). Thus, if the pitches you heard were a fifth apart then the ratio of motor speeds would have to be 3:2.

Another cause could be from the resonance in the leaf blower tube. This would be likened to the way a pipe organ operates. However, most leaf blowers are plastic which does not resonate very easily.

My guess would be that the noise was generated due to an imbalanced motor creating rigorous vibrations generating sound waves. It would be interesting to modify a leaf blower by extending the length of the tube and observing the difference in pitch (if any).