The open tunings of musical instruments involve changes in the frequencies of some strings, with a consequent change in tension. How much should be altered the diameter of a musical instrument string so that, as tuned above or below the pitch originally planned, the tension is kept as close as possible to the original of standard tuning? The answer to this question presents interest to physics teachers, since it involves various concepts of wave mechanics. The basic principles of wave physics applied to the strings are presented. Using these principles and the data given by the manufacturers, conclusions are established about the expected diameter of the strings. It is also proposed the construction of two string tension measuring devices for the occasions in which these data are not supplied by the manufacturers. One of the devices is more elaborate, while the other one is greatly simplified. Both data from the manufacturer and the proposed devices can provide an enrichment of lessons on wave physics.
wave mechanics; instruments tuning; open tunings; string tension
