2018 BFY III Abstract Detail Page

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Abstract Title: W19: Measurement of the Acoustic Impedance of an Air Column
Abstract: Resonances of strings and air columns are typically discussed during introductory physics courses, but greater in–depth discussions are reserved for courses such as the "Physics of Music" or similar and often are offered for non-science majors in pursuit of fulfilling their science requirement. Out of necessity the approach must be a qualitative one, since the mathematical background of this audience is not sufficient to allow for the solution of complex differential equations and boundary value problems. The acoustic impedance plays a central role when it comes to describing the propagation of sound waves in pipes of various shapes.  The concept of impedance is not terribly hard, but unfortunately it is a complex quantity (both literally and in the more general sense) and quite intractable for the student in a "poets course", or even some first year physics students. However, just like its electrical counterpart, the acoustic impedance may be measured straightforwardly with simple equipment usually found in a first-year physics laboratory or a well-equipped physics stock room. While it is beyond the typical poets-course student to calculate the impedance of a pipe with a flared bell, it turns out to be quite simple to measure it.  Comparison with the impedance of a standard cylindrical pipe of the same length allows to see the effect that the flared bell has on the resonances of the air column. In this way even students who do not have the mathematical sophistication of a senior physics or engineering major can learn to appreciate the subtleties that go into building a real musical instrument from a plain brass pipe, or why one type of trumpet mouthpiece sounds "brighter" than another one. In this workshop we introduce and demonstrate a simple device to measure the input impedance of a pipe or a musical instrument, a so-called "impedance probe".  The impedance probe consists of components that can be easily and inexpensively obtained from any mail order electronics parts company such as Mouser or Jameco, and assembled with tools and parts available at your local hardware store.
Abstract Type: Workshop

Author/Organizer Information

Primary Contact: Herbert Jaeger
Miami University

Workshop Documents

Workshop Doc 1: Download the Workshop Doc 1
Workshop Doc 2: Download the Workshop Doc 2
Workshop Doc 3: Download the Workshop Doc 3