A track can sound massive in your headphones and then fall apart the moment it plays anywhere else. The low end is almost always the reason. Phone speakers cannot reproduce a sub at all, club rigs expose every phase problem, and laptop speakers turn a muddy mix into noise. Here is how we mix kick and bass so they hold up everywhere, not just on the system you mixed on.
//The low end is two instruments sharing one room
Kick and bass both want the bottom of the spectrum, and there is not enough room for both to own it. The fix is to give them clear jobs. We usually let the kick own the punch around 50 to 100 Hz and let the bass own the sustained weight below that, or the other way around depending on the track. What matters is that they are not fighting over the same band. If both are fat in the same place, you get a muddy lump instead of two clear sounds.
//Sidechain so they take turns
We sidechain the bass to the kick. Every time the kick hits, the bass ducks for a fraction of a second, then comes right back. Your ear hears both clearly because they are never peaking at the exact same moment. Keep the ducking quick and subtle. If you can hear the bass pumping, it is too much. The goal is space, not a noticeable effect.
//Keep the bottom mono
Anything below roughly 100 to 120 Hz should be mono. Stereo information that low does not help you, and it actively hurts you on big systems where out-of-phase lows cancel out and disappear. Put a utility or a mid-side tool on your low end and collapse the bottom to mono. Your kick and sub get louder and tighter the moment you do this, because the energy stops cancelling itself.
//Check it on bad speakers on purpose
This is the step almost everyone skips. We listen on a phone speaker, on cheap earbuds, and in mono, every single mix. A phone has no sub at all, so if the bassline disappears, you are relying on frequencies most listeners will never hear. The fix is to make sure the harmonics of the bass, the part up around 200 Hz to 1 kHz, carry the note on their own. That way the bassline is still recognizable even when the sub is gone.
//A simple test that catches most problems
Bounce the track. Play it on your phone at the lowest volume that you can still hear. Then play it in the car. Then in mono on one earbud. If the groove between the kick and bass survives all three, your low end translates. If it falls apart on any of them, you found the problem before your listeners did.
Big systems forgive almost nothing, and phones reproduce almost nothing. A low end that survives both ends of that range will sound good on everything in between. That is the whole target.