Laptop: how do I control subwoofer volume independently of speaker volume?

[Moltke]

Many thanks again Moltke
Have a great day 

You're welcome! you too have a nice day. Glad you sorted it out!

Pulseaudio-equalizer: not listed in Ubuntu 16.04 repository (but I think is listed in 17.04),  so consequently sudo apt-get install pulseaudio-equalizer did not work

Yes, you're right. Sorry about that, I tried here and it worked, I didn't installed it but I had the option

Code:

The following additional packages will be installed:
  ladspa-sdk swh-plugins
The following NEW packages will be installed:
  ladspa-sdk pulseaudio-equalizer swh-plugins
0 upgraded, 3 newly installed, 0 to remove and 35 not upgraded.
Need to get 515 kB of archives.
After this operation, 2,309 kB of additional disk space will be used.
Do you want to continue? [Y/n]

I just didn't remember that I'd already added the ppa for another purpose few months ago  :, so in case you want to try again

Code:

$ sudo add-apt-repository ppa:nilarimogard/webupd8

then do

Code:

$ sudo apt-get update

and finally

Code:

sudo apt-get install pulseaudio-equalizer