# Sound Intensity and Power

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1. Mar 7, 2017

### Ian Baughman

1. The problem statement, all variables and given/known data
A speaker blares out music with a power of 10 W. Assuming the air has a temperature of 50°F and a pressure of 1 atm, what is the sound intensity level in decibels at a distance of 100m away? What is the maximum pressure variation at that point? What is the distance at which the intensity is 50 dB? The air has an effective molar mass M = 28.8 g and a ratio of heat capacities γ = 1.40.

2. Relevant equations

1) I = P/(4πr2)
2) β = (10 dB)log(I/I0)

3. The attempt at a solution

1) I used equation #1 where P = 10 W and r = 100 m to find:
I = 7.96 ×10-5 W/m2
2) This is where I'm having difficulty. I'm not quite sure on how to find I0. I know I can't use the above equation but I can't seem to find any other information that would be helpful.

2. Mar 7, 2017

### TSny

I0 is a standard value of intensity that should be given in your textbook or notes.

3. Mar 7, 2017

### Ian Baughman

So I found a value, I0 = 10-12 W/m2. Where does this value come from though?

4. Mar 7, 2017

5. Mar 7, 2017

Thank you!