Direct sound
Direct sound refers to the sound directly transmitted to the left and right ears of the listener.
Reflected sound
It refers to the sound that reaches the listener's ear after the initial reflection from the indoor surface, which is about ten to dozens of milliseconds later than the direct sound.
Reverb
It refers to that the sound passes through various boundary surfaces and obstacles repeatedly reflected irregularly in the hall, forming a lingering aftertone that diffuses throughout the space without direction.