Pyrophone

Steady amplitude against heater gain. Solid: stable, dashed: unstable. In the shaded band between the fold and the Hopf point a silent tube stays silent and a singing one keeps singing. Dots: the tubes sounding now.

The standing wave, strobed into slow motion. Gas slices move with the air (orange: compressed, blue: rarefied); the flame sits at x_f.

A note grows by itself out of the flame's noise, a line swelling over tens to hundreds of milliseconds before it holds steady. Below the threshold nothing appears at all.

(η₁, η̇₁/ω) of the focused tube. Inside the dashed cycle a sound dies; outside it spirals out to the solid one.