How to make a sliding door with good sound insulation

Sound insulation must be sealed first. The situation I think you said is that there is no track below. Is there a big gap if there is no track? There must be no gaps. Do not scratch the floor if there are gaps. Take it or make a track. The track is ready. The soundproofing is still not good. Just use some sound-absorbing materials. Generally soundproof doors are very thick.