If a material has a high absorption coefficient, what is the expected effect on a room's reverberation time?

• A. Reverberation time decreases.
• B. Reverberation time increases.
• C. Has no effect on reverberation time.
• D. Only affects bass frequencies.

Answer: (A)

High absorption means surfaces take in most of the incident sound instead of reflecting it. In a room, sound energy decays as it bounces around, and reverberation time measures how long it takes for that energy to die down. When absorption is high, more energy is removed with each bounce, so the sound dies out faster and the reverberation time becomes shorter. This relationship is captured by Sabine’s approximation: RT60 ≈ 0.161 V / A, where V is the room volume and A is the total absorption in sabins (A = sum α_i S_i). Increasing absorption, either by using materials with higher absorption coefficients or by adding more absorbing surface area, raises A and shortens RT60. While absorption varies with frequency, the overall effect is a reduction in reverberation time, not an increase, no effect, or a change limited only to bass frequencies.