To simplify the expression, the terms (1 + r 3 )P 0 can be simplified into an effective initial pressure, P * , to account for the air-receiving transducer reflection coefficient, r 3 , without explicitly solving for it as this quantity will be present in any transmission experiment through air, regardless of any material placed between the transducers. The remaining reflection coefficients are defined in Equation 13 and 14 where r 2 can be substituted with -r 1 as justified by film homogenization and the definition of the reflection coefficient.