Low End Bass build up = weak bass. Take a kick drum and bass line for instance. The kick is typically a consistent quick low note stab over and over again, and it is a note btw. But the bass synth or bass guitar lows are always moving around because the notes change. E1 is deeper and fatter than G1, the lower the “note”, the more low-end. Right, it’s obvious, but a loose basic rule of thumb would be to keep your kik drum not as fat as the bass line for most intentions. Disclaimer: this depends on what you want to accomplish with your music since music rules are not meant to be, but lets go with the popular end of the music universe here. A flabby kick and a loose bass is a common problem.
Bass power is also dependent on tempo. Slow tempos give room to lower, therefore slower bass notes. The deeper the note, the longer it takes for the bass note to complete. By the same token, a very low note can run into itself in faster tempo songs with definition and power being reduced.
Ever wonder why the kick crum and bass drop out a bit or get a little louder in a few spots in your song? It’s a safe bet they are phase canceling and/or summing a bit, which also makes it a timing issue. If you add second bass lines, 808 subs and all kinds of low end carnage playing together, you’ll have to manipulate the arrangement and/or automate the mix more to pull bass elements in and out so they are not conflicting with each other. EQ is helpful but it won’t really do the job of gaining definition with too many bass elements. The more definition, the more bass power.
Keep the low end simple and give it room to breath, you’ll end up with way fatter bass and more powerful results. Or, understand how to make it complicated in a fat way. The best way to get that is in your writing and recording arrangements.