While his star continues to rise, there are concerns over how exactly teen sensation Justin Bieber’s voice is dropping.

“Justin is physically developing at a slower rate than most guys so his voice is only breaking now,” a source tells the News of the World. “He’s working with the best in the business, a specialist called Jan Smith, to make sure he gets as much vocal rest as humanly possible for a working pop star. It’s the same people who worked with Usher when his voice broke.