The phenomena of sound are studied in the 1st grade of science classes in junior high school. As part of these topics, students mainly learn that sound is produced due to the vibration of objects, that it travels in waves, and that the properties of the waves determine loudness and pitch of sound. Sound is composed of three elements: loudness, pitch and timbre, but the focus is not on timbre at junior high school. However, students have plenty of experiences on differences of timbre in music classes as well as ordinary daily life, so learning about the details of timbre should also be possible in science classes. In this study, we propose teaching materials and methods to teach timbre effectively and understandably; we designed teaching materials to make students recognize differences in timbre, and to learn that the differences in timbre are caused by the differences in harmonics that produce the voice. We also practiced these methods in a junior high school to examine its educational effects. As a result, even junior high school students are able to understand the principle of timbre with the voice analysis, and therefore it is expected that the effect of learning about sound is enhanced.