psfred pretty much laid it out regarding door panel removal on the 400.However,you can not get to the sub speaker without removing the panel.If you attempt to access the speaker via the speaker covering on the door panel,you'll only crack the plastic covering.The speaker if OEM is fairly heavy duty with a large magnet in a sub woofer box.It's retained to the door frame with four nuts.There's also some type of sound retaining baffling around the speaker area.It could be updated if required.