Aerodynamic Generation of Sound Wind past a rod peels off a staggered street of vortices. Each one that leaves gives the rod a little sideways kick; that fluctuating force is a loudspeaker — the “Aeolian tone” you hear from a wire in the wind or a car aerial. The sound spreads as rings that are loud above and below the rod and silent straight upstream and down. The journey: Lighthill (1952) rewrote the flow equations so any unsteadiness looks like a sound source in still air. A force on a body radiates as a dipole: pressure ∝ cos θ / r, oscillating at the shedding frequency.