hi !
so is that green BA yours ? nice color
anyway. Yes the fronts are definitely 5x7s, and the rears are 6" I believe ( pretty sure. they might be 6.5" but i havnt looked for aages. )
The hardtop has 6x9s on the back shelf and nothing in the back doors i believe.
You can fit 6" in the front tho, or even 6.5". kinda depends on the frame of the speaker. But with some easily made baffles there should be no problem. I have 6.5" in the front at the moment.
If you want splits, then the tweeters can be placed wherever u want them in the front doors, on the dash or in the A pillars.
Another option is to cut or re-make the back shelf to hold speakers. easily done tho i reccomend u reinforce the shelf to make it a bit stronger. i think i used 6mm mdf wood and carpeted over it so it didnt look ugly.
depending on how much u want to spend there is actually a large selection of 5x7s available on the market, although not as common in stores as the other sizes. You may have to look at the brand's catalogue and order some in if ur shops dont have any on-shelf.
Boston have some 5x7 coax speakers that would sound beautiful ... or there are 5x7 splits available from brands such as Hertz.
The centre speaker in the BA hatch is 4" i think. As long as u ensure there is a signal to the centre speaker amp ( hanging above the ecu, under the stereo ) u can keep the sound to that too. Mazda were kind enough to follow the standard 4" mounting method with a square bracket and a screw in each corner rather than some other cars where there is a trangle on 2 sides with a single screw on each. Thanks Mazda !!
The stereo wiring diagram is available from the list of wiring diagrams available online. not sure of the link atm tho... You may have difficulty if u intend to upgrade the speaker wire running into each door as it takes some dismantling of the dash and then cutting up the wiring harness going out to the door.
I can provide diagrams from the mazda workshop manuals for Centre Speaker installation, Centre Amp Installation, Front and rear door speaker installation, rear shelf speaker installation ( hardtop ), stock head unit removal, Overall stereo layout, antenna removal/installation, full wiring diagram (online 1 is incomplete ), and wiring harness layouts for all elements ( stereo, amp, doors etc ). If ur interested i can scan and send those to u ...
If u intend for the article to include amp installation, then perhaps u could recommend some pathways for a power wire from battery to amp. Not too hard in the 1.8, but i had to dig around in my v6 to find a decent route.
look forward to reading it !
Dave