Best answer by AjTrek1
The Play 3 was a unique speaker in the Sonos line-up. Here are the characteristics:
1. One Play 3 positioned horizontality would play in stereo (L/R). However, after distancing one's self a few feet away the stereo separation would dissipate and the sound would become acoustically mono to the ear.
2. One Play 3 positioned vertically would play only as a Mono speaker
3. The preferred positioning of two (2) Play 3's is vertical to create a stereo pair (L/R). in this manner the Stereo effect was not limited by distance.
4. When used as surrounds the preferred position is vertical. In the Sonos app they could be set to FULL for playback of music and still serve as surrounds for video. Once set in the Sonos app the transition from Full to Surround mode was automatic.