* Reassuring: "The doctor's reassuring tone calmed the worried parents."
* Comforting: "The warm fire and soft music had a comforting effect."
* Soothing: "The soothing sound of the waves lulled her to sleep."
* Calming: "The calming scent of lavender helped her relax."
* Encouraging: "The coach's encouraging words motivated the team."
The best antonym for "disconcerting" depends on the specific context.