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Free Doppler effect calculator for classical sound in a stationary medium. Enter emitted frequency, speed of sound, and line-of-sight observer and source speeds to get observed frequency f′, shift in Hz, percent change, and wavelength context. Works alongside our wavelength and frequency tools and other math & science calculators.
Last updated: April 13, 2026
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Use the wave speed in the medium (not the speed of the source or observer).
Sign convention: positive if the observer moves toward the source along the line joining them.
Sign convention: positive if the source moves toward the observer.
Observed frequency f′
440 Hz
Δf
0 Hz
% shift
0%
λ in medium (v/f)
7.7955e-1 m
From emitted f
λ from f′
7.7955e-1 m
Spatial period at observed frequency
Formula used
f′ = f × (v + v_o) / (v − v_s)
Medium at rest; line-of-sight motion. Light uses different (relativistic) formulas—this tool is for sound-type waves.
Model textbook ambulance and train horn problems with consistent 1-D sign conventions.
Compare a moving speaker or microphone setup to the classical prediction for homework reports.
The same formula structure applies whenever your course uses a single wave speed in a stationary bulk medium.
f = 440 Hz, v = 343 m/s, observer stationary, source toward observer at 20 m/s → f′ ≈ 467.2446 Hz (higher pitch as the source approaches).
Wavelength in medium at emitted f: λ ≈ 7.7955e-1 m.
We evaluate the standard textbook relation for longitudinal waves when the medium itself is not moving as a whole. Your inputs define the emitted tone, how fast waves travel in that medium, and how fast the observer and source move along the line between them. The tool then reports the shifted frequency and simple wavelength companions using λ = v / f and λ′ = v / f′.
f′ = f × (v + v_o) / (v − v_s)v_o and v_s follow the sign rules shown in the calculator card. If v_s approaches v from below, f′ grows without bound in the model—so very near Mach 1 the ideal formula is only a teaching approximation.
1-D classical Doppler: moving source compresses or stretches wavelength; moving observer samples crests faster or slower.
Pair with the velocity calculator when problems mix constant-speed motion with wave quantities.
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