I have always found it best to cut a piece of fish tape to the size of a speaker template and poke a very small hole in the ceiling and poke around before cutting any holes.

I know it isn’t that fancey but it works great when someone else has done the pre-wire.

We use the flexible rod that comes with the Wet Noodle from LSD, http://www.lsdinc.com/content/product_details/62

Bend it to the right length, the rest is the handle.  Push the radius length section into your exploritory opening and rotate.  If something is in the way, it wont rotate 360°.  Saves drywall patching.  Do this before you scribe your circle too so you don’t have to try and erase your pencil marks.

Hey there morgan I was wondering if you knew the cost for that Wet Noodle kit? Thanks in advance for the tip.

my new house has 5 pre-wired outlets on the ceiling that the previous had installed as a option . still covered with switch plates .

Remember the blank plate is probably on a nail-on box on the rafter, and you should remove the box.  That can sometimes leave part of the rectangular hole left over from the nail-on box not being covered by the flange of the speaker!  (The speaker will hit the rafter or not allow the lugs to tighten up).  Keep some coat hangers bent at 90 degrees and the right length for the radius of the speaker to be used instead of cutting up your fishtape.  Wet noodle works great if you have one.

Such a wonderful topic for me…........