Q: What is the difference between STC, CSTC and CAC?

A: STC - Sound Transmission Class - sound reduction from one side of barrier to the other - walls; single pass rating.

CSTC - Ceiling STC - AMA 1-II-1967 Test Method - Two room test, measure of sound that passes through a ceiling across a common plenum and down through ceiling in adjacent (receiving) room; double pass.

CAC - Ceiling STC - ASTM E1414 - ASTM test method introduced in 1995; essentially replaced the AMA 1-II test.

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