Doppler Effect
Fly a sound source past a fixed observer — adjust its speed, true pitch, the speed of sound, and how close it passes to hear (and see, in the compressed and stretched wavefronts) the classic pitch glide, and watch a Mach cone form once it goes supersonic.
Preview — sign up free to change the numbers yourself
What you can adjust
- Source speed
- 0 – 510 m/s
- Source frequency (true pitch)
- 100 – 2000 Hz
- Speed of sound
- 100 – 500 m/s
- Observer distance (closest approach)
- 5 – 100 m
Above the speed of sound the source outruns its own wavefronts, piling them into a Mach cone (a sonic boom) instead of a smooth pitch glide.
The pitch the source actually emits — what the observer hears is shifted up while it approaches and down after it passes.
Lowering this makes the source go supersonic at a lower speed — 340 m/s is sound's real speed in air at room temperature.
How far below the source's flight line the observer stands — the closest distance the source ever gets to the observer.
About this simulation
What it shows
A sound source flies past a listener. The wavefronts bunch up ahead of it and stretch out behind, and the pitch an observer would hear glides from high to low as it passes.
The key idea
A source moving towards you squeezes the waves together so the pitch rises, and moving away stretches them so it falls. If the source is faster than the speed of sound, the wavefronts pile into a cone (a sonic boom).
Try this
Raise Source speed from 100 to 400 m/s while Speed of sound stays at 340 m/s: the source outruns its own sound and a Mach cone forms.