# Homework Help: Resulatant intensity level

1. Aug 8, 2014

### somecelxis

1. The problem statement, all variables and given/known data
A source prodeuces sound of intensity level of 30dB .If another source prodeuces sound at the same time , what's the resultant level?

2. Relevant equations

3. The attempt at a solution

the ans is 10 log (2$I_1$ / ($I_0$)) = 33dB , but why not = 10 log (4$I_1$ / ($I_0$)) .. beacuse when 2 sound waves superposed , the resultant amplitude is A+A= 2A , I is directly proportional to (A^2) ...

Last edited: Aug 8, 2014
2. Aug 8, 2014

### olivermsun

Are the two sounds correlated (e.g., in phase) with each other? The sum of the two will only have amplitude A + A (and therefore +6 dB) if they are perfectly in phase with each other. In general they're assumed uncorrelated (they have nothing to do with each other), and so you add the intensities and get +3 dB.

3. Aug 8, 2014

### somecelxis

it's not 3db am i right? the intensity now it's 2I ?

4. Aug 8, 2014

### olivermsun

33 dB is +3 dB relative to the original 30 dB, right?

Hint: log102 = ?