Rooftop HVAC Drone

How it's made

Source

three rooftop condenser fans. Pink-noise turbulence surrounds blade-pass tones at 85-165 Hz and weaker second/third harmonics; independent rotors create beating rather than a single mains buzz.

Body

compressors contribute 48-65 Hz vibration and 2x/3x partials. Broad sheet-metal/plenum modes at 175-320 Hz and 430-620 Hz colour the airflow, with Q below 1.5 to avoid ringing whistles.

Layers

high-passed brown pressure at 32-150 Hz, stereo exhaust at 130-3200 Hz, and a much quieter diffuse city wash at 90-850 Hz. Low machinery stays near centre; separated fan housings span the roof.

Envelope

continuous running, with no starts or stops. Load breathes by less than 8 percent over 5/10 s periods; slow independent drift moves the exhaust cutoff slightly without obvious gusts.

Loop

10 s; nominal rotor frequencies and periodic load modulation fit whole cycles. The renderer crossfades stochastic airflow across the seam. No impacts, switching clicks or baked-in room reverb.

Variation

seeded phase, airflow and drift differ per unit. Size lowers fan pitch; load brightens exhaust; distance removes high frequencies. Presets cover close fan, heavy bank, parapet and night roof.

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