I have gotten the art of round holes for speaker drivers down.
Unfortunately my current project includes an B&G Neo 8.
It is open baffle and I am using 1" thick Oak baffle material. My first try was with a "saw guide" & a router (zip tool in this case) using a 1/2" diameter straight bit. I was first going to do the counter sink so the Neo-8 sits more or less flush about a 1/4" deep cut. On one of the short ends the router went a little too far on the other short end I guess I tried to go "against the grain" and the tool chattered and tore out the side of my cut.
Since this piece of wood is more or less ruined I tried to use a hand held jig saw and the "saw guide" to cut all the way through for the part that needed to be cut through. I kept the edge of the saw tight to the saw guide but the blade took a different path, that wasn't straight.
I have given up for the evening, but I thought I would see if anyone had some advice.
I suppose I could try to cobble together a jig of some sort.