# DB question

1. Mar 6, 2006

### emma123

hi, i need help in understanding something on sound. if admam works near a jet plane that is taking off and experiences the sound level of 150dB. then the protectors to reduce the sould level to that of a chain saw, what decrease in dB is needed? i think it's 40 but i am not sure.
and also if Adam hears something that sounds like a whisper then what would a person w/o protectors hear? is there even a difference....

2. Mar 6, 2006

### physicsprasanna

The decibel is a logarithmic scale. The decibel level can be calculated by
$$\beta=10\log_{10}{\frac{I}{I_{0}}}$$

where $$I_{0}$$ is a constant reference intensity = $$10^{-12}W/m^{2}$$ This is roughly the intensity of a just audible sound.

Your problem can be solved only if the intensity of the chain saw is known.
I don't understand your problem .... sorry ....

who are those protectors??? and how can they reduce the sound of an aeroplane??

Last edited: Mar 6, 2006
3. Mar 6, 2006

### BobG

Your book should have a table with some common sound levels. Wikipedia has a table that is probably virtually identical with the table in your book (and, yes, that is a 40dB decrease).

Do you understand the relationship physicsprasanna gave? If you do, then you'll realize why decibels come in so handy. They turn a multiplication problem into an addition problem (i.e. - if the sound is the same as a barely audible whisper (0 dB), then a person without ear protection will hear a sound 40dB louder).

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