STC, a single numerical rating of sound transmission, is determined based on sounds of the frequency range typical of human speech. However, the primary outdoor noise sources – cars, motorcycles, trucks, elevated trains and air traffic – have strong low frequency content. The OITC was devised to more accurately represent the attenuation of these lower frequencies.
Because design techniques employed to seal an operable window against air leakage and sound transmission can have a direct effect on the force required to operate the unit, AAMA 1801-13 also requires testing for operating force to ensure compliance with applicable industry standards and codes.
“The recently updated AAMA 1801-13 includes some important information regarding the differences between STC and OITC,” notes Scott Warner (Architectural Testing), chair of the AAMA task group that developed the specification. “This updated AAMA document also clearly highlights the significance of measuring the air leakage, operating force and latching force before a product is tested for acoustical performance. Architects and owners can be confident that fenestration products, tested by accredited laboratories in accordance with AAMA 1801-13, are fully documented inclusive of the installation details and comprehensive description of the product tested.”