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Sound transmission class
Sound Transmission Class (or STC) is an integer rating of how well a building partition attenuates airborne sound. In the USA, it is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations (see ASTM International Classification E413 and E90). Outside the USA, the Sound Reduction Index (SRI) ISO index or its related indices are used. These are currently (2012) defined in the ISO - 140 series of standards (under revision).
The STC rating figure very roughly reflects the decibel reduction in noise that a partition can provide.
== Rating methodology ==
The ASTM test methods have changed every few years. Thus, STC results posted before 1999 may not produce the same results today, and the differences become wider as one goes further back in time–the differences in the applicable test methods between the 1970s and today being quite significant.
The STC number is derived from sound attenuation values tested at sixteen standard frequencies from 125 Hz to 4000 Hz. These Transmission Loss values are then plotted on a sound pressure level graph and the resulting curve is compared to a standard reference contour. Acoustical engineers fit these values to the appropriate ''TL'' Curve (or ''T''ransmission ''L''oss) to determine an STC rating. The measurement is accurate for speech sounds, but much less so for amplified music, mechanical equipment noise, transportation noise, or any sound with substantial low-frequency energy below 125 Hz. Sometimes, acoustical labs will measure TL at frequencies below the normal STC boundary of 125 Hz, possibly down to 50 Hz or lower, thus giving additional valuable data to evaluate transmission loss at very low frequencies, such as a subwoofer-rich home theater system would produce. Alternatively, Outdoor-Indoor Transmission Class (OITC) is a standard used for indicating the rate of transmission of sound between outdoor and indoor spaces in a structure that considers frequencies down to 80 Hz (Aircraft/Rail/Truck traffic) and is weighted more to lower frequencies.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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