Piece of cake Amie. No turning back after you start if you have second thoughts though. Once the recessed area in the log is bored out and chiseled to accept the speaker, there will never be any way to make it look original again. Personally, I’d not do it that way. I’d have built a cabinet to house it or go with a book shelf and mount it to the log.
To do it though, you just trace the area you need removed on the log that the speaker needs to slide into, take a drill with an auger bit to the log and remove what you can with the bit, then with a real sharp chisel, take out the rest of the log. If you want to put one in vertically that would span more than one log, it gets complicated. As the log shrink (and they will), the hole needs to be big enough to keep from crushing the speaker so one has to get pretty creative with trim to trim out the oversized hole.
