DESC: Definitive’s in-ceiling DI 4.5R speakers feature near-invisibility thanks to their small diameters, hidden flange design, and low profile micro-perf grilles. They are as easy to install as traditional flanged flush-mount speakers, and don’t require custom sheetrock/spackle skills to install yet they are practically invisible. The DI 4.5R is a mere 5-3/8 inches (13.55 centimeters) in diameter, about the same size as the mini recessed lighting fixtures that are all the rage in lighting design today.