# Sound question

#### physics1987

In my homework, I was assigned a question,
If two firecrackers produce a sound level of 95dB when fired simultaneously at a certain plance, what will be the sound level if only one is exploded ( hint: add intensities, not dB?

My immediate guess is to divide 95 in two, but it seems too simple, plus if it is only one fire cracker, would the sound level be 1/2 ? I don't think I am right, but can someone help me?
thanks

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#### LowlyPion

Homework Helper
In my homework, I was assigned a question,
If two firecrackers produce a sound level of 95dB when fired simultaneously at a certain plance, what will be the sound level if only one is exploded ( hint: add intensities, not dB?

My immediate guess is to divide 95 in two, but it seems too simple, plus if it is only one fire cracker, would the sound level be 1/2 ? I don't think I am right, but can someone help me?
thanks
Welcome to PF

What is the definition of a db?

#### physics1987

Welcome to PF

What is the definition of a db?
a decible (measured in hertz)

Homework Helper

#### physics1987

a decible (measured in hertz)
sorry, I got mixed up between frequency and dB...I guess my question is, is it possible to just divide dB by the amount of objects a noise is coming from?
ie. 3 sirens = 30dB
therefore 2 sirens =20dB?

#### LowlyPion

Homework Helper
sorry, I got mixed up between frequency and dB...I guess my question is, is it possible to just divide dB by the amount of objects a noise is coming from?
ie. 3 sirens = 30dB
therefore 2 sirens =20dB?
The sound intensity may be half in your example but that doesn't change the db's by half, because what is the a db?

It's a Log base 10 of the ratio of sound intensity to some reference.

So if Log10(P1/Po) = 95,

#### physics1987

The sound intensity may be half in your example but that doesn't change the db's by half, because what is the a db?

It's a Log base 10 of the ratio of sound intensity to some reference.

So if Log10(P1/Po) = 95,
thank you for the help,
I was able to solve for Intensity (P1) as .0031622777w/m squared
I then inputted this into the formula that you gave me to come up with the answer of 92, and I also double checked the formula and got the original answer of 95 for both firecrackers. Thank you so much!

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