there is a psychoacoustic phenomenon where the brain will synthesize a fundamental frequency where none exists.
http://en.wikipedia.org/wiki/Psychoacoustics#.27Phantom.27_f undamentals
So if you have enough harmonics of the fundamental, even though the speakers aren't producing it, your brain thinks there is.
If your bass or bass drums don't speak well on small speakers, you should work on sculpting your 100-500hz region to fool the ear into believing there are freqs between 50 and 100hz on smaller speaker. It doesn't take too much to work convincingly.
If you're dealing with pure sine wave type things like 808 bass drums and synth basses, then you have to find some other ways of building in some harmonic content. A little distortion can help generate that sometimes.
Also, compare your mixes to other professionally mixed stuff in the genre you're working in. You'd be surprised how much bass there isn't on those records.