Are sliding or barn doors soundproof enough for a bedroom?

Not by themselves. A sliding or barn door leaves gaps at the head, jambs and floor, so sound travels around the leaf no matter how dense it is — barn doors are decorative, not acoustic. For a bedroom that must be quiet, use a swing door with a solid core, perimeter seals and a drop-down door bottom; if you need sliding, specify a sealed acoustic track system with brush and drop seals.