ISO 354 (Absorption Measurement)

ISO 354:2003 specifies the method for measuring the sound absorption coefficient of acoustic materials in a reverberation chamber. The test involves measuring the reverberation time of the empty chamber and then with the test specimen (minimum 10–12 m²) installed, and calculating the absorption from the difference using the Sabine equation. Results are reported as random-incidence absorption coefficients at third-octave or octave bands from 100 Hz to 5000 Hz. The standard defines mounting conditions (Type A: directly on floor, Type E: with 200 mm air gap) that significantly affect low-frequency results. Absorption coefficients exceeding 1.0 are possible and valid due to edge diffraction effects. ISO 354 data is the basis for single-number ratings NRC (ASTM C423), SAA (ASTM C423), and αw (ISO 11654). All reputable acoustic product manufacturers publish ISO 354 test data for their products.