Coke Bottle Resonance
The cavity resonance frequencies of a 0.5 liter glass coke bottle were recorded by blowing over the top of it and measuring the frequency using a microphone and a digital frequency counter.
C* = constant for this experiment.
When the resonant frequency is plotted as a function of the inverse square root of the volume, a straight line plot is obtained. This shows that the frequency is proportional to the inverse square root of volume.
The calculated frequency of a resonant cavity depends upon the speed of sound v. It also depends upon the square roots of three physical parameters: the area of the opening A, the volume of the cavity V, and the length of the opening port L. The quantity C* indicated in the top graph includes the factors other than the volume which are held constant for these measurements.