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

Imagine a solo singer being joined by a large choir. The group will sound much louder, because there is now a lot more sound energy reaching your ears.

Sound is moving air. louder sounds are more moving air.

In your example, one person sings at 60dB (yes I know it is really a dBm thing but keeping it ELI5). If 10 people sang just as loud instead, there would be 10x the sound power, and the resulting sound level would be more like 70dB. If 100 folk sang, then the resulting ‘noise’ would be at about 80dB intensity.

Sound dB is a logarithmic scale, with each increase of 10dB actually being 10 times the power.

(I used singing in my example because groups singing create a much more organized sound than a bunch of folk just randomly speaking. So the song’s peaks and valleys of the sound waves align better, making a louder loud. Put enough folk together speaking randomly, and the result is a white noise with a lower overall intensity, as some of the sound waves will cancel out other sound waves)

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