Volume mutes when set below ~20% 14.04

Setting volume-limit works for headphones but will, probably, make sound too quiet while using other speakers.

As alternative solution, try setting ignore_dB=1 in /etc/pulse/default.pa.

load-module module-udev-detect ignore_dB=1

From ArchLinux Wiki

I found the solution here worked for me.

As root, you'll need to edit the file:

$ sudo vim /usr/share/pulseaudio/alsa-mixer/paths/analog-output.conf.common

Find the section that looks like the following:

[Element PCM]
switch = mute
volume = merge
override-map.1 = all
override-map.2 = all-left,all-right

Add a new setting for volume-limit so it looks like this:

[Element PCM]
switch = mute
volume = merge
volume-limit = 0.05    # This is the new line
override-map.1 = all
override-map.2 = all-left,all-right

Then you need to restart PulseAudio with the following command:

$ pulseaudio -k

If you had any applications playing sound, they will be muted. You'll have to restart them to get sound again and then you can test your new settings.

The original author of the solution suggested setting volume-limit = 0.01, but I found that to be too quiet, so I use 0.05. You can test smaller or larger values to fit your preferences.