Why does a siren sound higher as it comes closer and lower as it leaves?
The Siren's Sigh
Why does a siren sound higher as it comes closer and lower as it leaves?
You're standing on a corner when an ambulance races past. As it approaches, the siren wails high and bright. The instant it passes you, the pitch drops — like the sound itself sighed and slumped. You didn't imagine it. The siren never changed its note at all. So what just happened?
First, let's get sound straight. Sound travels in waves — tiny pulses of pressure pushing through the air, one after another, like ripples spreading across a pond after you toss in a pebble. Your ear catches each ripple as it arrives.
