What do 5.1, 7.2, 5.1.2 and similar channel numbers actually mean?

First number: ear-level speakers. Second: subwoofers. Third, where present: height channels for Dolby Atmos and DTS:X. That is the whole code.

So 5.1 is five speakers around you (front left, centre, front right, two surrounds) plus one sub. 7.1 adds two rear surrounds behind the seating. 5.1.2 keeps five around you and adds two height speakers, usually in the ceiling or as up-firing modules. 7.2.4 is seven around, two subs, four overhead. A receiver's channel count tells you how many of these it can drive at once; the layout you actually build can be smaller.

Is more automatically better? No. A well-placed 5.1 beats a badly placed 7.1.4 every time, and I have heard both in the same week. Surrounds sitting behind a pillar, rear surrounds crammed against the back wall thirty centimetres from your head, height speakers mounted where the false ceiling happened to have space rather than where the format wants them: each of those adds a channel and subtracts from the result.

What decides the right count is the room. Where the seats are: a sofa against the back wall leaves no room for rear surrounds, so 7.x is off the list and 5.x.2 or 5.x.4 becomes the better use of the same money. Where the walls are: an open-plan side means surrounds need to be placed and aimed with care. Whether the ceiling permits heights: a plain concrete slab is different from a false ceiling with access, and a very high ceiling changes the geometry.

Two subs (the .2) is one of the few "more" that usually helps, because two subs in different positions smooth out room modes across more than one seat. One sub can be excellent in one chair and thin in the next.

Sequence I would use: front three done well, sub integrated properly, then surrounds, then heights. Each layer adds less than the one before, so get the first layer right before paying for the fourth.

Send us a floor plan or a couple of photos with the seating marked and we will tell you which number fits, and which number you would be paying for and never hearing.