Glass bottles as wind musical instruments: An experimental method to predict the pitch based on the volume of water inside the bottle

The phenomenon of blowing on the neck of glass bottles and producing sound is very familiar to the general public. In fact, they can be treated as a professional set of wind musical instruments, as the musical group The Bottle Boys (http://thebottleboys.com/) do. With a certain collection of bottles, different tones can be obtained by varying the bottle shape, or the volume of water inside them, in a way that the pitch is higher as the volume of water increases. In this context, this work presents an experimental method to predict the volume of water necessary to get a specific musical note from blowing up at the neck of any general glass bottle, based on the fact that glass bottles behave like Helmholtz resonators. The method was applied using the free Android cell phone app Spectroid to measure the frequency of the sound produced by blowing the bottle, and also a graduated cylinder to measure the volumes of water, but common materials such as kitchen graduated cups can be used also. With this experimental setup, an experiment is done measuring the frequency of the sound produced by the glass bottle, relating it with its corresponding volume of water. After data acquisition, the Helmholtz resonator equation is applied to fit the data, and a characteristic curve of the bottle is established. With this result it is possible to predict how much volume is necessary to be insert in the bottle to obtain a desired musical note. Experimental errors are taking into account, three different types of bottles were analyzed to verify the validity of the method along with a commercial chromatic tuner by Korg, and tables relating the pitch and its corresponding volume of water for each bottle studied were produced from application of the method.