Measuring brass instruments: A 'physics of music'

Abstract

Among the various aspects of brass instruments studied in a Physics of Music class are physical dimensions such as tube length and bore profile. Although textbooks list values for instrument lengths and describe the significance of the cylindrical, conical, and flared sections of tubing, these parameters are not visually obvious in the coiled instrument. A laboratory exercise is described in which students make simple length and diameter measurements of real brass instruments. Plots of tube diameter vs. distance are produced that effectively display what each instrument would look like if straightened out. Students also determine the air paths through valves (which are surprisingly difficult to visualize), and measure the added tubing associated with each valve. Mouthpieces are examined and measured in order to demonstrate the complex set of shapes involved. These hands-on measurements force students to look closely at the component pieces, air paths, and construction details of the instruments. Pedagogically, the use of real instruments in the lab engages students and helps them make connections between the physics of ideal tubes and the design of real brass instruments. Student results and feedback are described.