bmw e39 sound install

[JOE///M]

Hi to everybody. i just joined . i have a an e39 530d 02 model. i want to upgrade basicly just the bass in my system. the vehicle currently has the 10 speaker with amp, non dsp unit. .this particular e39 unfortunately did not come with the optional ski openign or removable ski plate behind the rear arm rest . all solid metal which means some cutting's goin to get done. i have a JBL 15 inch subwoofer and 3000w audiobank amp wich will go in, however the install will basicly be a superwood board attached behind the rear seats, with sub free air mounted in the middle blasting out of the armrest opening. i have not stripped the seats as yet but my question is, what would an appropriate size hole be when i start cutting? i dont want sumting too small ,and also i dont want to damage anyting behind the seat for cos any bad scaring to the rear metal but at the same time i want enough of an opening for the sound to travel at its peak into the vehicle. will post pics as soon as i can get all my facts in order and begin with the prep. thanx for any responses.

[Jack Dabsy]

Just for starters... Looking into the trunk the seat-back trim should pop-off to expose the back-plate, it will not be a flat profile and may give you some idea of your chopping sizes !!