Helmholtz’s double siren locked phase while filtering each siren to one harmonic.

Evidence

Helmholtz’s circumvention of this problem led him to invent the double siren (figure 24.9). This ingenious device consisted of two independent sirens strongly coupled to tunable Helmholtz resonators. The resonators were supposed to filter out all the harmonics of the siren but one each, selected by adjusting the air volume of the brass chamber. The relative phase was adjustable by changing the timing of the puffs of air. The two siren disks rotated on a common shaft, guaranteeing that the frequencies produced by the two sirens would be locked into simple integer ratios depending only on the number of holes being played in a given disk. — Eric J. Heller, Why You Hear What You Hear- An…, 2248

Categorization

• DEFINE: Explains what a double siren is and how it solved the phase-amplitude coupling problem experimentally.