The XR Series Monitors are an update to the HR Series monitors but at a little more affordable price point.
The XR Series have the same logarithmic waveguide as the HR Series but with an updated kevlar woofer and a aluminium tweeter. The passive radiator on the back has been removed to save on cost.
Mackie have chosen to use an elliptical style port on the back to reduce the amount of turbulence coming out of the back of the speaker, allowing you to get a little bit closer to the wall.
For more info on the XR Series go to Mackie