Pop Bottle Resonator - May-June 2005

# Pop Bottle Resonator - May-June 2005 - TECHNIQUES FEATURE...

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May/June 2005 EXPERIMENTAL TECHNIQUES 67 N TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FEATURE My Favorite Experiment Series by R.M. French NEW SERIES A POP BOTTLE AS A HELMHOLZ RESONATOR T he Helmholz resonator is perhaps the simplest acoustic resonant system. The ideal Helmholz res- onator 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 (see Figure 1). It is assumed that the air volume acts as a mechanical spring and the air in the neck acts as a moving mass. The expression for the natural frequency of the system is 1 cA f 5 (1) ! 2 p tV Where c is the speed of sound, 2 A is the cross-sectional area of the port, t is the length of the neck and V is the volume. A familiar approximation to the ideal resonator is a 20 oz plastic pop bottle. Blowing over the top of the bottle makes a whistle whose frequency should be described by this ex- pression. EXPERIMENT As an experiment, the frequency of the sound made by blowing over the top of a bottle was measured with different liquid levels in the bottle. Figure 2 shows the bottle with the label removed and marks showing the different ±ll levels.

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## This note was uploaded on 02/21/2012 for the course MET 311 taught by Professor Markfrench during the Spring '12 term at Purdue.

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Pop Bottle Resonator - May-June 2005 - TECHNIQUES FEATURE...

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