• ALSA Utilities
  Install the alsa-utils package. This contains (among other utilities) the alsamixer and amixer utilities.

pacman -S alsa-utils

• Unmuting the channels
  ALSA by default has all channels muted, all of which will need to be unmuted manually. This can be done using amixer:

amixer sset Master unmute

This can alternatively be done using alsamixer:

alsamixer

• Test your changes

speaker-test -c 2

• User privileges
  Usually, local users have permission to play audio and change mixer levels.
  To allow remote users to use ALSA, you need to add those users to the audio
  group.

参考：https://wiki.archlinux.org/index.php/Advanced_Linux_Sound_Architecture