j3rvx

I had to remove the rear doorcard last week to sort a window squeal issue. I noticed my speakers have tweeters in the cone so I think I have the factory upgraded speakers but I'm not 100% on that one.

Although they sound decent enough I've been thinking about upgrading them for some better ones. I read somewhere you need adaptors to do this is this true? It looks like i could unscrew the current ones and screw aftermarket ones in, is there any reasons why people say you need adaptors? I don't want to buy some if I don't need them. Also I forgot to measure the speakers, does anyone know what size(s) I need? Are the fronts the same size as the rear?

Any help would be good thanks.