Sound Transmission Class (STC) is a single-number rating of the airborne sound transmission loss (TL) performance of a constructed assembly measured at standard one-third octave band frequencies.
The higher the STC rating, the more efficient the construction will be in reducing sound transmission within the frequency range of the test.
Outdoor/Indoor Transmission Class (OITC) is a number rating of the sound transmission loss of a constructed assembly tested with lower frequencies to represent sound typical of modes of transportation. OITC is of relevance to designers interested in how effectively their design will shield occupants from sound generated exterior to the structure.
More on sound attenuation.
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