Eyring Equation

The Eyring equation (also called the Eyring-Norris equation) is a reverberation time prediction formula that accounts for the reduction of sound energy at each reflection, making it more accurate than the Sabine equation for rooms with higher absorption. Published by Carl Eyring in 1930 and documented in ISO 3382-2:2008 Annex A.2, it uses the natural logarithm of (1 minus the average absorption coefficient) in the denominator. The Eyring equation converges to the Sabine equation when absorption is low and correctly predicts zero reverberation time when all surfaces are perfectly absorptive (α = 1). It is preferred for rooms with average absorption coefficients above 0.3, such as recording studios, anechoic chambers, and heavily treated classrooms. Like Sabine, it assumes a diffuse sound field, which limits accuracy in rooms with very non-uniform absorption distribution.