Separate echo applied to delay as refrected voice in the hall. This is a very important process in any surround processor. time delay is tipicaly several ten milliseconds, and this affects the tendency of surround effects.
As Rear Output Channels
Reverbration amplifire strengthened with power, and output to the rear speakers. In the actual case, the echo reaches the listener from all directions. However, the main speaker at the front plased normaly so that reverberations channel spot behind the listener to create surround effects.
See also Surround Audio Power Amplifier and learn How to make 5.1 channel amplifier and speaker setup