Find the quiet
between the notes.

Build a chorus, one pair at a time.

Choose the two weights in your repeating cell, then choose a stiffness for each link. The pair repeats indefinitely. Different masses or alternating spring links can split the vibration spectrum into two branches, with a gap between them.

The lower acoustic branch starts at zero frequency. The upper optical branch often moves the two weights against each other. The shaded interval contains no propagating mode in this ideal chain. A tone above both branches is also forbidden, but is not the gap a commission asks for.

Complete a commission: keep its hush tones inside the gap and its travel tones inside either branch’s range, staying within the mass allowance. Targets need a small margin from a band edge. Press Check chorus to earn a seal. All seven commissions are open. A little nudge changes one component toward a valid recipe; Undo returns one edit.

Use the wave-vector slider or tap the plot to explore motion from Γ (neighbors nearly in step) to the zone edge. Choose a branch, pause, or advance one step. Keyboard users can use all native controls with Tab, arrows and Enter. Hear mode maps the selected model frequency to a gentle audible tone.

The source dynamical-matrix assembler computes this two-mass harmonic chain. Units are dimensionless; the charms are illustrative weights, not measured materials. The motion preview is magnified. The plot shows allowed normal modes of an infinite periodic chain, rather than measured sound attenuation through a finite object.