The sound of bells
Harmonic and non-harmonic sounds with the study of the sound of bells
Autor:
Titre 4
Learning objectives :
This activity helps students understand the difference between harmonic and inharmonic sounds. It develops the ability to analyze the frequency spectrum and recognize the unique characteristics of instrumental timbre.
Concepts covered
Harmonic and inharmonic sounds; Spectral analysis; Musical timbre; Vibration modes; Music theory
What students will do :
The student analyzes and compares the frequency spectra of a bell and an oboe using FizziQ. By identifying the fundamental frequency and harmonics in each spectrum, the student discovers that the sound of an oboe is harmonic (integer multiple frequencies of the fundamental) while that of a bell is inharmonic, then explores other everyday objects to classify their sounds.
What is required :
Smartphone with the FizziQ application; Bell and oboe sound recordings from the Sound Library; Optional: various everyday sound objects; FizziQ experience notebook
Scientific background :
The difference between harmonic and inharmonic sounds is fundamental in musical acoustics and organology (study of instruments). A harmonic sound, such as that produced by an oboe, a flute or a guitar string, is characterized by a frequency spectrum following the harmonic series: f, 2f, 3f, 4f... where f is the fundamental frequency. This regular structure results from the mode of vibration of the instrument: a column of air or a vibrating string naturally generates standing waves whose frequencies are integer multiples of the fundamental. In contrast, an inharmonic sound, typical of bells, gongs or metal plates, presents a spectrum where the higher frequencies are not integer multiples of the fundamental. This irregularity is explained by the complex geometry of these objects which can vibrate simultaneously in several independent modes. In a bell, the vibration modes depend on its precise shape and the distribution of masses. Frequencies typically present include the "hum" (fundamental), the "third" (about 1.2 times the fundamental), the "fifth" (1.5 times), and the "octave" (2 times), but their exact ratio varies depending on the bell. It is this inharmonic structure that gives bells their distinctive and recognizable sound. FizziQ's frequency spectrum uses the Fast Fourier Transform (FFT) to decompose the sound signal and visualize these spectral components. The tool allows you to precisely identify the frequencies present in each sound and to directly observe this fundamental difference between harmonic and inharmonic instruments.