Even with pavucontrol set to 150% I can barely hear this thing. This low volume situation happens whenever I'm connected to LM 20 via bluetooth or USB. It does not happen when it's connected to my Android, to my iPad or to my Windows 10 machine.
It used to work well with my Linux machine before two things happened:
1. I updated to LM 20 2. I updated the firmware in the bluetooth device
I'm not too sure which of those two things caused the volume span to change but it was definitely one of them,
The device is a Bose Revolve Soundlink that is about 3 years old. If you understand Linux (especially Ubuntu Linux) you can see what troubleshooting steps have been taken so far by clicking this link.
In addition to these steps, I have also reset the Bose to factory settings and repaired and connected the speaker with the Linux machine. The problem remains.