A Helmholtz resonator experiment for the Listen Up project.

Abstract

The Listen Up project seeks to develop an educational booklet and apparatus that will be used to foster interest in acoustics and teach basic acoustical concepts to middle school students. The packaged kit must be low cost; hence this experiment uses a 16 oz plastic water bottle as a Helmholtz resonator, a disposable syringe, and an inexpensive pitch pipe. Understanding the Helmholtz resonator is fundamental to many applications in acoustics. A simple algebraic model of the device, derived from a mechanical mass‐spring analogy, relates the volume of air in the bottle to the resonance frequency of the system, and hence the pitch that is produced when one blows over the bottle opening. The volume of air inside the bottle can be easily and accurately controlled by adding water with a graduated syringe. The dependence of pitch on the volume of air in the bottle can be systematically demonstrated, and the validity of the model can be checked by comparing the sound produced to musical notes from the pitch pipe. This experiment yields a physical understanding of a common acoustical phenomenon and inspires further interest and study of more complex phenomena.