Another Look at Combination Tones

There have been many recent articles in this journal highlighting simple demonstrations of a wide variety of acoustic phenomena. In introductory physics courses, sound waves and their propagation through air, and resonance in musical instruments, are covered in detail. However, attention is not usually paid to the active role that our ears play in transforming sound waves to create various types of combination tones. Furthermore, many physics textbooks mention that pitch is related to frequency, but do not elaborate on the specifics of the relationship. Teaching the physics behind combination tones allows for an excellent application of physics to biology, and is also an interesting way of exploring the relationship between frequency and pitch. In the first part of the paper, the physics of human hearing and the theory behind combination tones is introduced. In the second part of the paper, demonstrations are outlined and the results are presented.