I think it might be worth the time to put a set of calipers on the speaker yourself and write down what it it comes up with. On the other hand, the hole being an 1/8 to 1/4 larger than it needed to be would be far less of an issue than the hole turning out too small.
I cut out some circles in 3/4" ply once with a jig set up beside a scroll saw. The jig wasn't that impressive either. 1/4" dowel in a block bolted to the same bench as the saw so that it stayed the same distance from the blade. I rotated the work piece on the peg as the blade passing it along the blade as it turned.
wbh1963 is flowing with the grain in Arlington, Washington, USA
A day without curls is like a day without sunshine!