The Mazda 3 is one of the most fun to drive small cars available in the U.S. today. It is a peppy car with plenty of power and space for four people and all their gear. Upgrading the stereo is relatively easy to do. The head unit can be replaced with a more advanced unit, and there is plenty of space in the trunk for a subwoofer. Depending on whether the sub is installed in the sedan or the hatchback model, you may want to adjust the positioning slightly, but the basic procedure is the same.
Measure the space in the trunk where you would like to place the subwoofer. With the hatchback, you can mount the sub along the side of the trunk or along the rear seats. With the sedan, it may be better to position it parallel to the rear seats, but the sub can also be mounted along one side.
Measure the sub enclosure to make sure it will fit in the space you have selected.
Connect the subwoofer to the terminal cup with speaker wire. Mount the subwoofer in the sub enclosure and secure it with screws and a screwdriver.
Attach at least two strips of heavy-duty Velcro to the bottom of the sub enclosure with wood glue. Make the strips as long as possible so the sub will stay in place when mounted. Attach two corresponding strips on the carpet of the trunk with fabric glue.
Connect the speaker wire to the amplifier and run the wires through the car to the trunk, close to where you'll mount the sub. You can run them under the edge of the plastic trim by lifting it slightly with a screwdriver or you can unclip the trim pieces. These pieces are attached by clips and are easy to remove.
Connect the speaker wire to the back of the sub enclosure and place the sub enclosure firmly on the Velcro.
