help with sound waves!

[tmkgemini]

The graph shows the US Department of Labor noise regulation for working without ear protection. A machinist is in an environment where the ambient sound level is of 85dB, i.e., corresponding to the 8 Hours/day noise level. The machinist likes to listen to music, and plays a Boom Box at an average level of 84.0dB. Calculate the INCREASE in the sound level from the ambient work environment level (in dB).


You don't really need the graph for this part of the problem... I have no idea how to solve this... i have the hint :Compute the intensities from the levels, add them to get the total intensity, then find the total sound level. Note the question asks for the increase..... but it's still not helping. PLease help!!!

[Andrew Mason]

The graph shows the US Department of Labor noise regulation for working without ear protection. A machinist is in an environment where the ambient sound level is of 85dB, i.e., corresponding to the 8 Hours/day noise level. The machinist likes to listen to music, and plays a Boom Box at an average level of 84.0dB. Calculate the INCREASE in the sound level from the ambient work environment level (in dB).


You don't really need the graph for this part of the problem... I have no idea how to solve this... i have the hint :Compute the intensities from the levels, add them to get the total intensity, then find the total sound level. Note the question asks for the increase..... but it's still not helping. PLease help!!!
Since difference in loudness in decibels between sounds A and B is 10log(I_A/I_B), a sound A that is x db louder than sound B has an intensity (Power/Area) of 10^(x/10) times the intensity of B. If you add these two sounds together you get a combined intensity or Power/Area of I_A + I_B. So the new loudness in decibels increases by 10log((I_A + I_B)/I_B). There will only be a few db difference by combining the two sounds.

AM