iOS Universal Utilities
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:
Or just use Calculate Decibels
-Optimized for iPhone5, iPad mini and iOS 6