Question

Sabine's formula for reverberation time derivation

Answer 1

The first part is deriving that the time derivative dW/dt of the acoustic energy W is proportional to the acoustic energy. From that it follows that the acoustic energy must decay exponentially, with the time constant derived above tau_W = 4V/(cA). T60 (T30) is defined as the time by which the acoustic energy has decayed by -60 dB (-30 dB) = 10^-6 (10^-3). tau_W is defined as the time by which the acoustic energy has decayed by 1/e. T60 and T30 are just tau_W multiplied by constants.