Sound Intensity

[Salty]

When a single person shouts at a football game, the sound intensity level at the center of the field is 60 dB. When all the people shout together the intensity level increases to 109 dB. Assuming that each person generates the same sound intensity at the center of the field, how many people are at the game?

[James R]

What's the relationship between sound intensity level and intensity? Do you know the relevant equation?

Hint: Sound intensity level is measured in decibels. Intensity is measured in Watts per square metre.