Approaching sources sound higher and receding sources sound lower because the waves are bunched up or stretched out.
How to use the Doppler Effect Calculator
- Source frequency
- Source speed toward listener
- Listener speed toward source
- Speed of sound
Results update as you type, and every field accepts the units shown in its menu.
How it works
The emitted frequency is scaled by the ratio of wave speeds relative to the observer and source.
Inputs explained
| Field | What to enter |
|---|---|
| Source frequency | Units: Hz, kHz, MHz, GHz |
| Source speed toward listener | Units: m/s, km/h, mph, ft/s, knots |
| Listener speed toward source | Units: m/s, km/h, mph, ft/s, knots |
| Speed of sound | Units: m/s, km/h, mph, ft/s, knots |
What each result means
- Observed frequency = [Source frequency] × ([Speed of sound] + [Listener speed toward source]) ÷ ([Speed of sound] – [Source speed toward listener])
- After passing (moving apart) = [Source frequency] × ([Speed of sound] – [Listener speed toward source]) ÷ ([Speed of sound] + [Source speed toward listener])
Example values
How the main result changes when Source frequency changes and everything else stays at the example values above:
| Source frequency (Hz) | Observed frequency (Hz) |
|---|---|
| 350 | 377.52 |
| 525 | 566.27 |
| 700 | 755.03 |
| 875 | 943.79 |
| 1,050 | 1,132.55 |
| 1,400 | 1,510.06 |
Formula
f′ = f × (v + v_observer) ÷ (v − v_source) (positive speeds = moving toward each other)Worked example
Inputs — Source frequency: 700 Hz; Source speed toward listener: 25 m/s; Listener speed toward source: 0 m/s; Speed of sound: 343 m/s.
Results — Observed frequency = 755.03 Hz; After passing (moving apart) = 652.45 Hz.
Frequently asked questions
Does the Doppler effect apply to light?
Yes; astronomers use redshift to measure how fast galaxies recede.
What happens if the source moves faster than sound?
A shock wave, the sonic boom, forms.
What formula does the Doppler Effect Calculator use?
f′ = f × (v + v_observer) ÷ (v − v_source) (positive speeds = moving toward each other).