Book 14, Question 111
Why Does Clapping Between Two Flat Walls Make a Zinging Sound?
Clapping between two flat walls makes a zinging sound called a flutter echo! The sound bounces back and forth between the walls, and each bounce is a tiny echo. They come so quickly that they blend into a buzzy ping.
More fun facts
- Flutter echo is a well known sound effect that happens when sound waves bounce back and forth between two flat, parallel surfaces that reflect sound.
- A sharp sound like a clap works well, because it is much shorter than the time sound takes to cross between the walls.
- Someone standing between the walls hears a quick series of repeated pulses of the clap.
- The time between repeats depends on twice the distance between the walls divided by the speed of sound.
- In one room with walls 8.1 metres apart, the repeats came about every 47 thousandths of a second.
- In ordinary rooms, the flutter fades slowest at middle pitches around 1 to 2 kilohertz, which gives flutter echo its typical middle pitched sound.
- Sound engineers at Aalto University and EPFL have even recreated flutter echo as a special effect for music, games and virtual reality.
Questions kids ask
How do builders stop flutter echo?
They cover one wall with something soft or bumpy, or tilt the walls so they are not exactly parallel.
Where can I hear flutter echo?
Try clapping in a long, narrow hallway or a stairwell with hard, bare walls.