JBL MTC-447MR Ceiling Speaker Mud Ring Bracket for Control 447C/T & 447LP (Pack of 6)The JBL MTC 447MR is an optional MR plaster ring bracket used to prepare Control 400 Series ceiling speaker installations in sheetrock applications. It helps define speaker location before the wallboard is installed and supports a cleaner installation workflow. Its circular offset forms an edge guide for plastering, while the bracket wings attach to the building structure. In production style jobs, it can also serve as a reference for repeated cutout