Truck Air Horn

How it's made

Source

compressed air drives two or three diaphragms into sustained periodic vibration. Sixteen explicitly bounded harmonics per diaphragm model the asymmetric, brassy pressure wave.

Body

long flared horns have fundamentals of 140-250 Hz; unequal tube lengths form a low chord. Harmonic weights emphasize the 700 and 1500 Hz radiation bands, with a smooth upper rolloff.

Envelope

pressure builds over 65-95 ms, holds with a small sag, then vents over 130 ms. Pitch rises about 2.5 percent into lock and drops 1.8 percent as pressure is released.

Layers

quiet band-limited turbulent air accompanies the tone; valve opening and closing add rounded 75-120 ms air puffs. The result is dry and centered, without a baked-in room.

Modulation

shared pressure wander and tiny independent tuning movement animate the sustain. Higher harmonics bloom after onset and darken on release; no clipping supplies the brass edge.

Variation

named random streams vary tuning by 0.15 percent, onset by 3 ms and harmonic phase. Presets offer a highway twin, heavy low triple, compact warning and weathered wide twin.

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