🚨 Doppler Effect Calculator
Find the frequency an observer hears when the source or listener is moving — the approaching/receding toggles handle the tricky signs for you.
Observed frequency f′
482.173 Hz
Higher pitch (blue-shifted)
f′ = f·(v ± v_observer)/(v ∓ v_source) — signs handled by the approaching/receding toggles. 🔒 Computed in your browser.
How the doppler effect calculator works
The Doppler effect shifts the observed frequency: f′ = f·(v ± v_observer)/(v ∓ v_source), where v is the wave (sound) speed. Approaching raises the pitch, receding lowers it. Set each speed and its direction, and the tool applies the correct signs and reports the observed frequency and whether it is higher or lower.
The sign convention is exactly what students and chatbots get wrong. Here the approaching/receding buttons set the signs, so you can’t apply them backwards. If the source reaches the wave speed, a shock wave forms and ordinary Doppler no longer applies.
Frequently asked questions
What is the Doppler effect?
The change in observed frequency (pitch) when a source or observer moves relative to the medium. Approaching raises the frequency; receding lowers it — the reason a siren drops in pitch as it passes.
What is the Doppler formula?
f′ = f·(v ± v_observer)/(v ∓ v_source), with v the speed of sound. The signs depend on direction; this tool sets them from the approaching/receding toggles.
Why does the pitch drop as a car passes?
While approaching, the sound waves are compressed (higher frequency); once it passes and recedes, they are stretched (lower frequency) — a sudden drop as it goes by.
What speed of sound should I use?
About 343 m/s in air at 20 °C (the default). It varies with temperature and medium; enter the appropriate value.
What happens at the speed of sound?
When the source reaches the wave speed, the waves pile up into a shock wave (a sonic boom) and the simple Doppler formula no longer applies.