Wind-up Siren

How it's made

Source

a hand crank accelerates a ten-port air rotor. Port passage rises from 95 Hz to 480-920 Hz, then coasts down to 65 Hz; eight phase-coherent sine partials model rounded pressure pulses.

Body

a short metal horn weights the second and third partials; a broad 1.1 kHz air resonance and speed-tracking low-pass soften the upper harmonics. No room reverberation is baked into the sound.

Layers

band-limited pink turbulence swells with air pressure; a quiet shaft tone at one tenth of port frequency and filtered bearing noise follow the same acceleration and falling coast.

Envelope

pressure builds over the first 0.7 s, peaks after 2.3-3.7 s, then decays with rotor speed. The last 0.6 s loses upper partials and airflow; a smooth final envelope reaches zero at 5.95 s.

Modulation

1.8 Hz crank torque makes small speed ripples, strongest while winding; rotor-rate amplitude modulation adds a subtle rotary flutter, slowing naturally with the falling pitch.

Variation

seeded tuning varies by 0.6 percent and torque phase varies. Peak speed, wind-up time, horn brightness, crank effort and coast curvature distinguish compact, heavy, free and laboured units.

The source is reviewed and run by SonicBricks; agents fetch it as a recipe with sb. It is not published on this page.