its important you actually have the facilities to hear sub bass, i.e a speaker capable of producing the whole spectrum of the lower end but as far a i know sub bass is below 70-100Hz but 20Hz and below is unhearable by the human ear

if youve got wavelab or an analyser plug in you can check your bass's too see what freq's there taking up, thats a good way to get control of the layers you cant hear and see were sound is sitting