Doppler Effect Calculator
Calculate the observed frequency shift from a moving sound source.
Assumptions used in this calculation
- Stationary observer, moving source: Assumes a stationary observer and a source moving directly toward or away from them (not at an angle), through still air.
About this calculator
An ambulance siren sounds noticeably higher-pitched as it approaches and drops as it passes, a real acoustic effect, not an illusion, caused by the source's motion compressing or stretching sound waves relative to a stationary listener. This calculator computes that observed frequency shift using the Doppler effect equations for sound: for an approaching source, f' = f × v ÷ (v − vs), and for a receding source, f' = f × v ÷ (v + vs), where f is the source's true frequency, v is the speed of sound (default 343 m/s), and vs is the source's velocity. Enter the source frequency, its speed, direction, and the speed of sound, and it returns the frequency an observer actually hears. Because the source's motion either compresses wavelengths (raising pitch) or stretches them (lowering pitch) depending on direction, the two formulas use opposite signs in the denominator, a detail that's easy to flip by mistake when working it out manually. This models a stationary observer and a source moving directly toward or away, not at an angle.
Worked example
500Hz siren approaching at 30 m/s
Result: 548.9 Hz
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