Peter L. Hoekje
Dept. of Phys., Univ. of Northern Iowa, Cedar Falls, IA 50614-0150
The acoustics of ducts presents a rich spectrum of practical student laboratory activities, from exposition of basic wave physics to exploration of important characteristics of musical wind instruments. A variety of duct experiments will be described, extracted from a musical acoustics course for music majors and a junior level vibrations course for physics majors at the University of Northern Iowa, as well as from an advanced acoustics seminar at Northern Illinois University. Basic physical phenomena explored include resonance, wave speed, and wavelength. These can be extended to open-end corrections, pressure, and velocity in a standing wave, acoustic impedance, and the dependence of sound speed on temperature, pressure, and gas composition. Wind instrument frequency responses can be easily observed. Small bore perturbations shift normal mode frequencies, demonstrating that resonance frequencies are affected by bore shape. Many of the experiments described use an inexpensive impedance head built by students from a piezoelectric driver and an electret microphone. This device can be customized for specific apparatus, and stimulates discussion of transducer design and use. Overall, students use simple apparatus to build a foundation of conceptual understanding which can be extended to fruitful research.