Acoustics Many building codes and standards contain requirements for the acoustic performance of walls, doors, windows, ceilings and other architectural elements. These sound control measures shield building occupants from excessive noise. ASSA ABLOY has opening solutions that provide exceptional acoustical control that align with targeted Sound Transmission Class (STC) ratings. The Science of Sound Transmission Reduction The STC of a door is determined through sealed-in-place acoustic testing. Testing conforms to ASTM E90-2009 Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements. Acoustic Door Testing is done on “sealed-in-place” doors for door STC ratings, as well as on assemblies (withgasketing and door bottoms) for operable STC ratings. Operable STC ratings are always equal to or lower than the sealed-in-place ratings. The best performance rating on the operable test is a “zero drop” in the assembly's STC rating. For example, a door with an STC 45 rating can only achieve an operable STC of 45 at its very best; it can never achieve a STC 50.