Volume low even at maximum

Try the PCM settings in alsamixer - Open terminal (Ctrl+Alt+T) and type alsamixer:

You may need to select the sound card with F6 first.

Turning up all the other controls may also help

1. Open terminal Ctrl + Alt + T

2. Install PavuControl sudo apt install pavucontrol

3. Open PulseAudio Volume Control pavucontrol

4. Output devices Set to 100% (0dB) the port are you using (Speakers / Headphones etc)

You should enable "Louder than 100%" in sound settings.
This works at least in Ubuntu 17.10

This works 100%...

• right click on volume icon located at top right corner of screen (ubuntu 16 )
• Select sound settings
• Go to application section and raise volume up :D enjoy your high sound..

If you were using GNOME 3, definitely you don't need pavucontrol or alsamixer. Instead just use gnome-tweaks to enable over-amplification (in the General tab, or in the Audio tab if any)