For anyone that is interested in the accuracy of different methods of acoustic testing (computer modeling vs. real world accuracy) for determining the STC of a wall assembly, Sound & Vibration Magazine has an article in its December 2014 issue.
It covers the testing comparison of the different methods, using four types of wall assemblies.
A very interesting note is the drop-in efficiency of all of the drywall assemblies between 1500 Hz. and 4000 Hz., as compared with a 6″ concrete wall.
Read the full article here: Computer Modeling of STC – Options and Accuracy, by Daniel M. Horan