We are considering installing soundproofing in our home, but would first like to determine if it will make enough of a difference.

I would like to know how you can calculate the effective reduction in decibels if a supplier claims their product reduces the noise level by 50% or 70%, etc.

Because the decibel scale is logarithmic, I am unsure how this works and I assume it is not just a simple matter of reducing any given decibel reading by the claimed percentage reduction to obtain the new decibel figure.

For example, if I know traffic passing our house generates a decibel reading of 80dB and the soundproofing claims to reduce that noise level by 50%, then I assume the reduced decibel reading would not be 40dB?

Is there a formula that can be used to calculate the resulting decibel figure after a percentage reduction has been applied to a decibel reading?

Thanks for any help.