Reflected waves’ timing pulls a reed’s buzzing frequency toward the tube’s resonance

Evidence

What happens when the sloshing frequency of the water trumpet is higher than the natural buzzing frequency of the valve? The reflected waves will arrive earlier than the valve would want. Now an important consideration arises: with the water level rising from an early arrival, the float can overpower the spring, causing the valve to open early, forcing the valve period closer to the sloshing frequency. Similarly, if the buzzing frequency of the valve is somewhat higher than the sloshing frequency, the late arrival of the crests will delay the valve. Every lip-reed player knows that the playing frequency slides into preferred frequency zones near its natural resonances as the buzzing frequency is changed. Notes can be “lipped” sharp or flat, but they stay in a groove near a resonance frequency until the frequency abruptly pops out and lands in an adjacent groove. It is very difficult to play halfway between grooves in the lower registers. — Eric J. Heller, Why You Hear What You Hear- An…, 1550

Categorization

• DEFINE: The water-trumpet mechanism is a concrete mechanical model of how wind-instrument feedback locks playing frequency to resonance grooves.
• XREF: Connects to the earlier violin Helmholtz-kink discussion and to Whyte’s pitch-locking phenomena from the audience-perception literature.