Should just be able to use a metal file, thats all I used, just have to have some patients, I wasn't able to get my hands on anything power, so it was really my only option, 2 hours later, I had both speakers installed.
I would recommend sticking with smaller components that will fit in the rear pod. you will get the best sound from the front, and will barely hear the back. I'm debating to remove my rear speakers so the sub has space to move the sound. honestly the back speakers are NOT important, unless you carry lots of passengers and want to please them.
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WTB:
2 Left Front + 2 Right Front E46 Fenders
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