how to know the what is our default audio device ? /dev/audio or /dev/dsp in ubuntu?

I was trying to play random songs command line using mpg123. But did not know what is my default audio device.. or if I need to specify any other audio device with the '-a' option. Both /dev/audio and /dev/dsp are audio devices. How to know which one is default ?

From stackoverflow

• The default sound system is ALSA and /dev/audio or /dev/dsp (OSS interfaces, deprecated in Linux) is only an emulation layer over ALSA -- and not even a fully functional one, at that.

  The default ALSA device is "default", and if you install mpg123-alsa, it should Do The Right Thing without requiring any options.