The OITC rating system measures the transmission of street sounds (such as car horns, sirens, construction, and low-flying airplanes) through exterior walls, windows, doors, and other facade elements. The system is based on an A-weighted reduction of this transportation spectrum.
Exterior transportation noise tends to have a lower frequency than interior noise (such as voices), so the OITC rating system emphasizes low-frequency sounds in its calculations. The difference between this transportation spectrum and the transmission loss data measured in ASTM E90 STC tests is used to calculate OITC ratings as per ASTM Test Procedure E1332.
In addition to acoustical evaluations, NGC Testing Services also has capabilities to conduct tests on these types of exterior products and systems for fire performance, wind load, water penetration, and air infiltration.