If you have a bass track in a mix which sounds great on big speakers but disappears completely when played on smaller speakers then here are a few tricks which can help.

Distortion

Adding some distortion on the bass either via an insert effect or from a parallel bass distortion channel will add some grit and harmonics.   This technique works well on dense mixes like rock for example where there is some flexibility in the bass tone.

MaxxBass

Waves make a great plug-in and hardware box called MaxxBass which generates harmonics based on a frequency you set.  These harmonics trick the ear into perceiving low bass frequencies that may not actually be present in the output. This technique works well for the most natural sounding enhancement to your original bass and ensuring translation across different sets of speakers.

Chorus

A slight bit of chorus can help to make the bass pop out on smaller speakers.  Send a split of the signal to a buss, EQ out the really low end (we don't need this), and then chorus the top end of the bass.  Blend to taste with the original signal.