Sub-bass (20–60 Hz): felt more than heard — the physical rumble of explosions, kick drums, and synth bass. Requires a subwoofer or large monitors (8-inch+ woofers) to reproduce. Upper bass (60–250 Hz): contains the fundamental frequencies of bass guitar, kick drum, and lower piano notes — provides warmth and body.
Most 5-inch studio monitors roll off around 50–60 Hz — you cannot accurately judge sub-bass on them. For electronic music and hip-hop production, a subwoofer or larger monitors are essential.