A Pop Bottle as a Helmholz Resonator

This resource, published in the Experimental Techniques journal, describes an experiment related to the Helmholz resonator. "The Helmholz resonator is perhaps the simplest acoustic resonant system. The ideal Helmholz resonator consists of an air volume enclosed with rigid walls and vented through a neck whose cross-sectional area is small compared to the dimensions of the volume." In the experiment a 20 ounce plastic bottle is used to measure frequencies of sound by filling it with different amounts of liquid and blowing over the top of the bottle. "Using several different fluid levels to vary the enclosed air volume, the parameters in the Helmholz equation can be identified so that the calculated frequencies are within a few percent of the measured ones."