. . . "R" . . . "The Sound Reduction Index is used to measure the level of sound insulation provided by a structure such as a wall, window, door, or ventilator." . . "Sound reduction index"@en . "belongs to SOQ-ISO" . "http://en.wikipedia.org/wiki/Sound_reduction_index"^^ . "\\(R = 10 \\log (\\frac{1}{\\tau}) dB\\), where \\(\\tau\\) is the transmission factor."^^ .