The XR400-CM is a true midrange and should not be used below 250 Hz. Specifically engineered for high efficiency and smooth midrange with a treated pulp cone body and a butyl rubber surround, this driver will reproduce smooth, dynamic midrange without the need for a great deal of air volume behind it. Detachable mounting tabs and a unique "minimum diameter" grille system allow this speaker to be installed in areas that are too tight for normal 4-inch speakers. Packaged as a single driver with matching grille included.
I went my own way trying to build my own jl brand F1 system from alpine i went with the xr 5.25 comp and added these 4" xr's and it is rocking with the jl 300x2 amp for the price it is a good set up