Reducible Experimental Deviations between ISO 354 and ASTM C- 423

The main standards used to determine the sound absorption coefficient (α) of materials in the reverberation room are ISO 354 and ASTM C- 423. Really there is a difference between the two standards. The materials with the highest sound absorption determined by ASTM C423 standards (αTM) increases more than that determined by ISO 354 standards (αIS) and decreases as the ability of the material decrease to absorb sound, as in the case of wood. The number of source locations has no effect on the sound absorption of materials. To reduce the difference between ISO (αIS) and ASTM (αTM) methods for sound absorption measurements, a new idea of a sample area was proposed with 9.36m2 and only two locations for sample placement in the reverberation room. The sound absorption coefficient (αNA) of (9.36m2 ) approximates the findings of the sound absorption coefficient in highly absorbent materials with ISO standards method, and vice versa for low absorption materials, when the sound absorption coefficient results converge with ASTM standards. For all situations of source locations (2, 3, 4), the sound absorption average (SAA) established by ASTM standards is greater than that determined by ISO standards for high sound-absorbing materials (rockwool (k), polyurethane sponge (s)), and vice versa for weakly absorbing materials (wood (w)). In the reverberation room, the relative standard deviation ranged from 0.01 to 0.04.