Bluetooth speaker connected but not listed in sound output

One way to solve the problem is to:

1. unpair the device
2. run the following command on terminal: sudo pkill pulseaudio
3. and then pair again the speaker via bluetooth.

The speaker is now displayed on the output audio list, which needs to selected for obtaining output sound.

Remember to, under Sound Settings, change Mode to High Fidelity Playback (A2DP Sink).

This is what is working for me for Bose QuietComfort 35 on Ubuntu 16.04. pauvcontrol didn't do it for me, and neither did the numerous settings changes and module loadings recommended elsewhere. So give this a try:

1. Install blueman

   sudo apt install blueman
   

2. Delete the paired device in the bluetooth settings.

3. Run these commands in terminal:

   $ sudo pkill pulseaudio
   $ sudo /etc/init.d/bluetooth restart
   

4. Turn off headphones.

5. Turn on headphones, and press green/go until headphones notification voice says "Ready to pair."

6. Launch blueman, and from the upper right menu, right-click the icon to bring up the blueman menu. Select Setup new device.

7. Pair the device, and when you are given an option, not Headphones, not Handsfree. Use the Audio sink option.

8. Then when you look into the audio settings panel, the device should be displayed.