sound wave?

Question

The sound of a band is rated as 50 dB at a distance of 30.0 m. What is the dB sound level of the band when one is 10.0 m from the band??

please help me, thanks!!

Answer 1

Ok, I was looking in the book for that theory, I was forgetting it, but I have it now :

I1 = P / 4*pi*r1^2

I2 = P / 4*pi*r2^2

B2 - B1 = 10db(log(I2 / Io - log(I1 / Io))

B2 - B1 = 10db(Log(I2 / I1))

And from : I1 = P / 4*pi*r1^2

I2 = P / 4*pi*r2^2

I2 / I1 = r1^2 / r2^2

then : r1 = 30 ; r2 = 10

B2 - 50 = 10log( 900/100)

B2 = 59.5 Db

Hope that helped you

Note : B1 ; B1 = intensity of the sound in DB