Question

The front row of a concert has a sound level of 120 dB and an IPod produces 100 dB. How many IPods would be needed to produce the same intensity as the front row of the concert?

Answer 1

Since the `dB`-scale is logarithmic, it turns multiplying into adding.

Originally it was the `Bell`-scale, purely logarithmic, where "times 10" is translated into "plus 1" (just like normal logs). But then the steps became too big so they divided the `Bell` in 10 parts, the `deciBell`.
The levels above could well have been called `10B` and `12B`.

So now, ten times the sound means adding `10` to the `dB`'s, and vice versa.

Going from 100 to 120 equals 2 steps of ten.
These are equivalent to 2 times multiplying by 10.

Answer : you will need `10*10=100` iPods