Why is cumulative sound louder?

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This is definitely stupid, think I’m missing something.

If I say something at 60 decibels for example, the person I’m talking to will hear it at that volume (ignoring the sound lost over distance).

But if a crowd of people say something at 60 decibels, it will be louder to the person hearing it.

I just can’t get my head around why, since they’re all talking at the same volume as the single person. What amplifies it?

In: Physics

7 Answers

Anonymous 0 Comments

It’s like the opposite of noise cancelling headphones. They have a microphone that picks up on incoming sounds. It then creates a sound that completely cancels out the noise.

Waves (including sound waves) can interfere with each other destructively (make quieter) or constructively (make louder). The (effectively) random nature of sounds in a room means that there’s going to be a lot of constructive and destructive interference at once.

You can visualize this by throwing sand in a still body of water. One grain of sand doesn’t make very large waves. Throw a fistful of sand and you will see a lot of waves, some large and some small.

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