Question

In ncert book chapter sound, it is written that normal conversation' s loudness is 20 decibels and 80+ decibels are painful. But in class rooms where almost 20 pairs of children were , why doesn't it painful for us that time

Answer 1

20 pairs of children = 40 children. Decibels = 80 
1 children = 2 decibels. 
but there are other objects also. such as bench ,desk,classroom. They also absorb sound .Some sound also echo .Hence, It is not painful

Answer 2

20 pairs of children = 40 children. Decibels = 80
1 children = 2 decibels.
but there are other objects also. such as bench ,desk,classroom. They also absorb sound .Some sound also echo .Hence, It is not painful