Picture of the Add button on the Sony SRS XB21 speaker.

Sony XB21 Add Button Explained

The ADD button on the Sony XB21 enables you join from two to ten compatible speakers such that both play the same program. The ADD button joins two XB21s for Stereo or Double modes.  It’s the bottom button on the rear buttons panel, just below the WPC button, and to the left of the USB power input port.

Picture of the Add button on the Sony XB21.
The Sony XB21 Add button.


Sony XB21 ADD Button: How it Works

How to Set Up a Stereo Pair with the ADD Button on the Sony XB21

The Stereo Pairing function lets you join two XB21s such that one plays the left channel of the stereo program, while the other plays the right channel.  Now to create a stereo pair, you need two SRS XB21s. Pairing the 21 with speakers other than an identical model did not work in our tests, and the Sony documentation states that you must have two of the same model in Bluetooth range of each other for connecting the two as a stereo pair to work.

Picture of the ADD lamp glowing white on the Sony XB21.
The ADD lamp glowing white on the Sony XB21.

Setting Up SRS XB21 Stereo Pair Mode with the ADD Button

Now To form a stereo pair of two XB21 speakers, do as follows.

    1. Power up the first speaker.  We’ll call this XB21  Speaker One.
    2. Press the ADD button on Speaker One for three seconds. The ADD light will start starts blinking white when the speaker beeps. E.g. See this lamp in the last picture above. After a few seconds, it stops flashing, and starts glowing solid white.
    3. Next, turn on the second XB21.  I.e. Speaker Two.
    4. As you did on Speaker One, press and hold the ADD button on Speaker Two  for three seconds.  Again on this speaker, the ADD light will begin flashing just as it did on the first one.  And also, it assumes a solid white glow after several seconds.
    5. No go to your Bluetooth source device, and connect it to the speaker pair, called “SRS-XB21”.  If you do not see this device, the move your phone / tablet closer to the speaker whose Pairing lamp is flashing.
    6. Finally, once you connect to the new stereo pair, you can start playing music on that device. Then it will stream to that speaker pair, and you’ll hear the program in STEREO!

Reversing Stereo Channels with the ADD Button

When in Stereo Pair mode, each speaker is assigned one of the two stereo channels (either L or R).  The speaker you press the button on will announce which channel is playing.

Note that there are no L and R lamps on this particular speaker.  So you’ll have to rely on the voice assistance announcements as you press the ADD button, to tell you which speaker is playing which channel.

Now with the ADD button, you can reverse these assignments such that Speaker One plays the right channel while Speaker Two plays the left. To do that, simply press and release the ADD button repeatedly on either speaker until it announces the channel it will play that you desire.

Ending Stereo Pair Mode

When you’re ready to break the stereo pairing, simply press and hold the ADD button on one of the speakers for three seconds.  A tone then sounds and the ADD lamp goes out, indicating that the pairing is now over.

Picture of the dark ADD lamp on the Sony XB21.
The dark ADD lamp on the Sony XB21.

Setting Up SRS XB21 Double Mode with the ADD Button

When two XB21 speaker operate in Double Mode, both speakers play a monaural version of the music. I.e. They both play the sum (L + R) of the left and right stereo channels.

To establish Double Mode, you set up the two speakers just like you did for stereo mode. Then, press and release the ADD button on one of the speakers until that speaker announces that it is now in double mode.

Related Posts to Sony XB21 ADD Button

    1. SRS XB10 Add Button Explained
    2. Sony XB20 Add Button Explained
    3. Sony XB12 Add Button Explained

Other Sony XB21 Posts

    1. How to Pair Sony XB21
    2. Sony XB21 Factory Reset Instructions
    3. Sony XB21 Specifications
    4. How to Check Sony XB21 Battery Life
    5. Sony XB21 Not Charging


    1. Official Sony XB21 Support Page
    2. Where to Buy the Sony XB21

Revision History

    • 2023-03-18: First published.