Now we know that the frequency of a sound wave is the number of cycles that pass an observation point per second. Thus, the velocity of propagation of a sound wave is its wavelength times its frequency. One opening was put to the ear, the other directed at the sound source. By using a series of these Helmholtz was able to estimate the strengths of the harmonics of a periodic sound. He also found the frequencies of inharmonic partials of bells and gongs.
Resonances have a noticeable effect on the timbre of musical sounds.
For brass instruments this is controlled by the length and shape of tubing, and how the player constricts the lips. For woodwind instruments, their tubular structures are resonators whose resonant frequencies are controlled by opening or closing various holes. The vocal tract has several resonances that emphasize various ranges of frequency in the sound produced by the vibration of the vocal cords. By changing the shape of the vocal tract, the frequencies of these resonances or formats determine which vowel sound is produced. The resonances of the soundboard of a violin greatly affect the timbre.