It's best to add these baffles for protection when you install door speakers. I would recommend cutting a port for the bass on the bottom - you have to cut a hole for the speaker wires anyway.
You gotta use the baffle........
from Corona California
I've been buying these baffles for years. Every time I do a speaker install. Not only do these protect the back side of the speaker from dirt and moisture( yes, they both get inside your doors), but they also act as a gasket around your speake mount to provide vibration free mounting. OH, almost forgot the most important part: they keep the bass response clean and tight, coming out the front of the speakers and not filling you door........ If you don't use these for your installs, you should be. Even if you Matt your doors....
Protect your speakers
My 08 Cobalt coupe is leaking water in the doors (apparently somewhat of a common issue). My factory speakers went dead due to corrosion from all the water. I put in new Pioneer 2-way speakers (part of a Bluetooth stereo and 4 speaker set, by the way great). I didn't feel like spending money for new speakers every year, so I gutted out the factory speaker frame (since they were dead) and mounted the new speakers into the frame, and between them I put the baffles.
People complain that it kills their bass. I don't expect much bass from my 6.5" door 2-way speakers to begin with, but I did what the customer reps told me - cut a small hole on the bottom (not on top, so the water doesn't drip in it, this way it'll slide on the sides and not come in from the bottom defying gravity). You will need the hole to connect the wires anyway, and it fits in nicely.
Also, since they offer two depth, chat with the representative. I almost ordered the big ones, until the knowledgeable staff told me my Cobalt only has so many inches of room in the doors and that I needed the "slim" version.
Installs fairly easy and helps attenuate rattling in the door.
They work as advertised. Only challenge was the snug fit on Drivers side door/window. Had to ultimately cut the back the baffle so it didn't slow down the window in my daughters Ford Fiesta. May have worked fine if the Driver side window motor wasn't starting to show signs of weakness (and will ultimately need to be replaced). Only reason for 4 stars was based on my results due to my window motor, otherwise 5*