This app allows you to add and subtract limitless sound source decibel levels together to give a total sound db level.
Sound levels are generally expressed in decibels, which are logarithmic and so cannot be manipulated without being converted back to a linear scale. You must first antilog each number, add or subtract and then log them again in the following way:
I1+I2+...+IN=10*Log10(10^(I1/10)+10^(I2/10)+....+10^(IN/10))
Or just use Calculate Decibels