Okay, well they won't be "perfect" in the most literal sense of the word, but they're pretty damn close.
Not sure if anyone has covered this or how you guys do it. I also think a lot of us take for granted that everyone knows how to do these little things. So I thought I'd share the way I do it. Maybe everybody knows this little trick already. I dunno.
Don't have a Jasper jig and plunge router and all that jazz? Me neither. All you need is a piece of scrap wood, really. The other stuff you'll already have. A screw. A pencil. And a tape measure.
First... cut a little piece of scrap. Doesn't have to be very wide or very long. Measure 1" out from one end for your pivot point. Put a screw there. Then all you need is the sub cutout. My 12 spoke 12's are right at 11" so I need the radius of that which is just half. So, 5.5". Either measure 5.5" from the pivot point (screw) or 6.5" from the end to account for the screw spot. Then drill a hole at that spot JUST big enough for your pencil.
You can see here that I use this same little jig for my 10's and 12's and this thing has probably drawn over 100 circles. Lol.
The tighter you can get this, the more consistent your circles will be.
Now, this is how I center my subs on the baffle. I find the center line like so...
The just draw an 'X' from the corner of the baffle to the corner of the center line. This is obviously to center (2) subs.
'X' marks the spot. There's your centers.
Take your little circle jig and screw it into the middle of the 'X'.
Now just drag it around.
Bingo. There you have it. A pair of perfectly centered, beautiful circles. Whether they look like that after you and your jigsaw get done with them is on you. Lol.