What do the numbers mean?

For example, in a 9.1.4 home theatre setup:
The first number “9” describes how many speaker channels are present in your setup — left, right, center and rear speakers.

The second number “.1” describes the addition of a subwoofer for more bass or the all new Sound Motion technology in Sonos Arc Ultra soundbar.

The third number “.4” describes the number of upward firing speakers for overhead sound.

Together, they build an immersive surround sound experience right at home.