When HomePod shipped earlier this year, it could only be used individually. But Apple promised a software update that would support stereo pairs and multi-room capability, as found on competing wireless speakers such as those sold by Sonos.
The newly released iOS 11.4 delivers support for HomePod stereo pairs. Apple describes the feature thus: "Each HomePod is able to play its own audio channel — left or right — while separating out both the ambient and direct energy. This innovative stereo sound provides a wide, almost three dimensional soundstage for an incredible listening experience anywhere in the room. A HomePod stereo pair creates room filling sound with greater bass extension, resulting in a deeper, more accurate reproduction of low frequencies."
Set-up is said to be easy, because setting up a second HomePod in the same room triggers the option of creating a stereo pair. Only one HomePod in a pair responds to Siri requests.
In addition to HomePod, speakers from Bang & Olufsen, Bluesound, Bose, Bowers & Wilkins, Denon, Libratone, Marantz, Marshall, Naim, Pioneer and Sonos are expected to support AirPlay 2.