The Physics of Music

Introduction

It was at my initial interview for the assistant professor position at Middle Tennessee State University (MTSU) that I was posed a question that would have the greatest impact on my teaching and research. I was told that at MTSU the Recording Industry degree program was the largest major on campus, yet none of their students took any physics courses. How, I was asked, would I change that situation? I suggested that a custom Physics of Music course would appeal to those students because, like their discipline, it merged topics from both technical and aesthetic angles. In my first year as a faculty member I developed a syllabus and proposed the course to the Recording Industry Department. They were very enthusiastic and supportive. When I arrived at MTSU, I had never had a physics of music course or any real background in acoustics, so I had the joy of learning new material as I developed and taught the course for the first time. In a familiar example in which the divisions between teaching and research start to dissolve, I began to be fascinated by acoustics and its relation and similarities to my core discipline of optics. My research interests moved into the realm of acoustics such that now more than half of my publications at MTSU are in the area of acoustics. So began my path in acoustics.

What is the Physics of Music?

The most common initial reaction when I say I teach a Physics of Music course is what has physics got to do with music? As I discovered in developing the course, the two subjects are beautifully entwined. Both are concerned with wave and signal phenomena. Common physics concepts, such as examining signals in both the time and frequency domains, are central to understanding the musical concepts of pitch, timbre, intervals, and scales. Similarly, the mathematics of music is logarithmic, an octave in music corresponds to a multiplication by two of a base frequency, not an additive step. The concept of loudness is similarly multiplicative as embodied in the decibel scale. Although many of the recording industry students came into the class with significant math and science phobia, I worked hard to make the material both accessible and relevant to their discipline. The fact that the students could see the subject as important to their chosen profession motivated them to grapple with concepts and methods they would otherwise have avoided. The Recording Industry students were most unlike the pre-med, physics majors, and engineering technology students in my other classes. Particularly on concepts in music and room acoustics, they were animated, opinionated, and very vocal about the class material; they asked lots of challenging questions. Many of my classes turn into excellent protracted class discussions. Those discussions taught me to look carefully at a variety of acoustics issues more closely—I learned a lot! I also learned what issues were of particular interest to the students. I added material to the class on the subjects of room and architectural acoustics because these topics generated lots of attention.

One aspect of the Physics of Music course that was particularly valuable was the requirement of a final project. It was my attempt to inject some ideas of research into the course and it proved to be both popular and, at times, awe-inspiring. My preferred project was that students build a simple musical instrument and test and describe its acoustic properties in terms of the concepts developed in the class. During the last two class periods of each semester I have the students present their results including, if appropriate, a demonstration of their instrument. Over the years I have seen, semester after semester, the most creative collection of musical instruments and performances: from tuned PVC pipe marimbas, to home-carved mandolins, guitars, and banjos, theramins, flutes, and drums of all descriptions. The students share these inventions with both pride and with humor: their presentation allows them to demonstrate their own musical skills (Free Bird has been played countless times), and they happily reveal the mistakes, miscalculations, and learning curves they experienced along the way. That is the essence of scientific research.

Didjeridu Adventures

Students would often donate their project instruments to me at the end of the class. For many years the department of physics and astronomy had a display case featuring their creations. One instrument in particular led me down an interesting path. A student in an early class donated the didjeridu, a traditional Australian aboriginal instrument. The didjeridu is an excellent example of an instrument that makes a note based on the standing wave resonances in a tube closed at one end. It’s a topic that is covered extensively in my course. Using the donated didj I did some simple frequency analysis experiments and posted a feature entitled The Physics of the Didjeridu on my MTSU webpage. I was pleased to find, over the years, that my webpage became enthusiastically followed on the internet amongst “didj” enthusiasts. As a result, I was interviewed by Roland Pease of the BBC World Service for a series of programs (sorry, programmes) called Sound Works that he was putting together on the science of music. Part of the interview involved me playing the didjeridu. It is somewhat daunting to imagine that my less-than-stellar didjeridu skills were played by the BBC for all the world to hear! You can hear the interview, complete with my questionable didjeridu playing, here.

A second result of my didj expertise was that I was asked by James Gordon, a researcher at the University of Leeds in the UK, to design a didjeridu that would create tones in the infrasound regime (below the frequency that humans can hear). The purpose of such an instrument was for use as an elephant deterrent device by subsistence farmers in sub-Saharan Africa. The experience taught me both the power of the Web to reach an audience around the world as well as the pervasiveness of physics in all aspects of life. Why do I count the Physics of Music course as a particular teaching achievement? The course clearly influenced me as it changed my research path; acoustics forms a significant portion of my publications and has resulted in a couple of patents. What impact did the course have on students? Over the years I have seen the influence on various individual students. A handful, based on my class, chose to apply to graduate programs in architectural acoustics programs, a move that caused them to take many more math courses than they anticipated. One student was fascinated by my lecture on how the ear operates and a discussion of the use of cochlear implants. He asked how he could get into that field of research. I advised him to look at audiology. Over the next few years he would occasionally communicate with me as he worked his way through audiology programs ending with his obtaining a doctorate in audiology and working as the director of a program on cochlear implants. Based on my class, a number of Recording Industry students decided that their interests were, instead, in pursuing a physics degree. Over the years the physics department has garnered a handful of majors, including some of our most talented ones, from Recording Industry. A measure of the importance of this course that doesn’t depend on individual student stories lies in the fact that the course began as an elective course for the Recording Industry students. It is now a requirement that RI students either take the Physics of Music course before their final (candidacy) year or they take RIM 4100 post-candidacy which Recording Industry developed in consultation with Physics as an upper level course that replicates, in large part, the material covered in the Physics of Music.

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Phone: 615-838-7301
Email: bill@robertsonscience.com
Address: 1310 Roberts Road, Goodlettsville, TN, USA