Doppler Effect Calculator
Doppler Effect Calculator
The Doppler effect is the change in a wave's observed frequency caused by relative motion between the source and the observer - it's why a siren sounds higher-pitched as it approaches and lower-pitched as it passes and moves away. Enter the source frequency, the speed of sound in the medium, and how fast the source and observer are each moving (positive values mean moving toward each other), and this calculator finds the frequency you'd actually hear.
- f_o = f_s × (v_sound + v_observer) / (v_sound - v_source), so a 700 Hz siren moving toward a stationary listener at 30 m/s (v_sound = 343 m/s) sounds like 700 × 343 / 313 ≈ 767 Hz.
- Sign convention matters: a positive source velocity means the source is moving toward the observer (raising the pitch), and a positive observer velocity means the observer is moving toward the source (also raising the pitch) - use negative values for motion away.
- This is why sirens change pitch as they pass you - the frequency is higher while approaching (source velocity positive) and drops noticeably the moment it passes and starts moving away (source velocity becomes negative).
How do I calculate the Doppler-shifted frequency?
Use f_o = f_s × (v_sound + v_observer) / (v_sound - v_source), with positive velocities for motion toward the other party.
What frequency do you hear from a 700 Hz siren approaching at 30 m/s?
f_o = 700 × (343 + 0) / (343 - 30) = 700 × 343 / 313 ≈ 767 Hz - noticeably higher than the siren's actual 700 Hz.
Doppler Effect Calculator
The Doppler effect is the change in a wave's observed frequency caused by relative motion between the source and the observer - it's why a siren sounds higher-pitched as it approaches and lower-pitched as it passes and moves away. Enter the source frequency, the speed of sound in the medium, and how fast the source and observer are each moving (positive values mean moving toward each other), and this calculator finds the frequency you'd actually hear.
- f_o = f_s × (v_sound + v_observer) / (v_sound - v_source), so a 700 Hz siren moving toward a stationary listener at 30 m/s (v_sound = 343 m/s) sounds like 700 × 343 / 313 ≈ 767 Hz.
- Sign convention matters: a positive source velocity means the source is moving toward the observer (raising the pitch), and a positive observer velocity means the observer is moving toward the source (also raising the pitch) - use negative values for motion away.
- This is why sirens change pitch as they pass you - the frequency is higher while approaching (source velocity positive) and drops noticeably the moment it passes and starts moving away (source velocity becomes negative).
How do I calculate the Doppler-shifted frequency?
Use f_o = f_s × (v_sound + v_observer) / (v_sound - v_source), with positive velocities for motion toward the other party.
What frequency do you hear from a 700 Hz siren approaching at 30 m/s?
f_o = 700 × (343 + 0) / (343 - 30) = 700 × 343 / 313 ≈ 767 Hz - noticeably higher than the siren's actual 700 Hz.