Do I need a separate subwoofer for good bass?

It depends on the bar. Across the reviewers we read, all-in-one bars like the Sonos Arc Ultra and Amazon Fire TV Soundbar Plus get praise for their built-in bass, but most expert sources still note they fall short of a dedicated sub for movies. Bars that ship with a wireless subwoofer — like the JBL Bar 500MK2, Ultimea Skywave X70, and Polk Signa S2 — were consistently called out for more impactful low-end.