The QT Sound Control Delta IIC rating shows what the product adds to the assembly in terms of isolating impact footfall noise. The QT Sound Control Delta IIC test starts by testing a full assembly, typically six to eight inches of concrete, with nothing above or below the concrete. Then an underlayment installs directly to the concrete, and the same test repeats. The QT Sound Control Delta IIC rating is the performance gain between the first and second test. A higher number shows better performance.
The QT Sound Control (Ecore) Delta IIC rating is the best rating to consider when comparing the performance of different types of underlayment. It keeps the manufacturers from promoting misleading results obtained by using materials or methods of isolation that the average assembly does not use. Misleading results are most often found with claims of 60 IIC or above using materials less than 1/2” thick. They achieve their astronomical rating with decoupled ceilings and considerable additional mass, but will claim their thin underlayment is what achieved that IIC rating. If the IIC rating is unreasonably high, then ask to see a Delta IIC rating. If they cannot provide a Delta IIC rating, then ignore the advertised ratings. See this chart to see how the main players in the acoustical underlayment business compare to each other.http://qtsoundcontrol.com/astm-e2179-ratings/ .