Reverberation time is defined as the time it takes for sound to decay by how many decibels from its direct signal?

• A. 60 decibels
• B. 20 decibels
• C. 100 decibels
• D. 10 decibels

Answer: (A)

Reverberation time is a measure of how long a space continues to sound after the source stops. The standard definition uses a drop of 60 decibels from the initial sound level (the direct signal) as the sound decays. This 60 dB criterion gives a practical, widely used benchmark for how long the room’s reflections linger, which is why RT60 is the common metric in acoustics. If you used smaller drops like 20 or 10 dB, you’d describe a much quicker fading that doesn’t reflect the full reverberant tail; a drop of 100 dB would imply an unrealistically large decay and isn’t used. So the time for the sound to fall by 60 decibels is the standard definition.