If you want it to look like a profesional job, take it to a professional who has the skills, knowledge, and abilities! The word CAN'T never gets a job done and you CAN use your existing speakers to make a template! However, it does require the aforementioned skills, knowledge, and ability. You might try taking a piece of thin cardboard (template material), cut out a hole big enough to clear the tweeter, place it over the speaker assy and them turn it face down supported by a couple of spacers (2 x 4s or books) so the tweeter if not touching your working surface. Now trace around the outside of the speaker....remove the template from the speaker. Now replicate the area on the speaker that will constitutes the speaker opening and transfer it to the template.....make your final cuts on the template and now you have your installation template! Sounds harder than it is.