7.1 channel refers to the use of four surround speakers.
The function of 7.1 channel is simply to establish a set of relatively balanced sound fields around the listener. 7.1 surround is virtual. In fact, there are only five sound zones (left front surround, right front surround, center surround, left rear surround and right rear surround). The remaining 2 sound zones (left surround and right surround) are allocated from the main sound zone.
The difference between 7.1 channel and 5.1 channel is that it adds the rear middle channel on the original basis. At the same time, it is also different from the ordinary 6.1 channel, because 7.1 channel has two rear middle channels.
Because people's ears are divided into left and right. At this time, if there is only a central speaker behind you, the sound field will deviate. This deviation will sometimes cause you to think that the sound is closer to the left, because your left ear receives the sound first, and sometimes you will think that the sound is on the right, and the sound field will not have a three-dimensional feeling, which is almost a flat sound.