Sony SRS-XB31 Help Manual page 42

When using the Speaker Add function, the codec automatically switches to SBC.
You can also operate the Speaker Add function on "Sony | Music Center."
Note
If you reset or initialize one of the two speakers while using the Speaker Add function, make sure to turn off the other speaker. If
you do not turn off the other speaker before restarting the Speaker Add function, there may be problems in making a
BLUETOOTH connection and outputting sound.
When you make a BLUETOOTH connection by One-touch (NFC), touch the speaker in which the
flashes. The device cannot make a BLUETOOTH connection with the speaker when the
off.
If a portable audio device, etc. is connected to the speaker's AUDIO IN jack, the speaker automatically switches to AUDIO IN
mode, and the Speaker Add function is terminated.
When watching movies using the Speaker Add function, there may be a gap between video and audio.
Related Topic
Switching between double mode and stereo mode (Speaker Add function)
What you can do with "Sony | Music Center"
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(BLUETOOTH) indicator
(BLUETOOTH) indicator is turned