speakers

Hey guys new to this site. I just bought my 2015 wrx base model. I was curious if I'm able to upgrade the head unit from out of a newer model into mine. And also if the speakers from Newer model will just fit right into my car.

I have for sale a complete set Logitech Z-680 THX-Dolby Digital DTS 5.1 Surround Sound Speakers with Subwoofer. Less than 1 year old and in very good condition. The Logitech Z-680 gives you THX-certified theater-quality digital sound. Both optical and coaxial inputs provide for simple...

so the front door speakers are 4" and the rear ones are 5 1/4". i bought two of each size and then i started looking around at tutorials on how to take the door panels off safely and how to replace the speakers. I noticed that the speakers and the mounts only have 3 holes for screws to hold them...