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.

Frequency Volume Hz cm3 355 100 310 125 280 150 256 175 239 200 225 225 212 250 202 275 193 300 185 325 178 350 171 375 165 400 161 425 156 450 152 475 146 500

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.