Time to start the major construction project for the car...the sub enclosure.
Keeping with the "keep it hidden" goal of the build, I decided to build a 4th order and send the port through the rear deck. This puts all sound created by the subs in the cabin area and eliminates the possibility of a flappy trunk...which means I don't need to waste sound deadening in the trunk. An added bonus of this configuration is that the port is horn loaded off the rear glass.
To seal off the trunk from the cabin area (to increase SPL numbers in BOBOS competition) I made templates then cut 1/2" plywood to fill the open areas in the structure behind the rear seat back. I used a layer of CLD/CCF deadener on the front side of the new wall to seal the wall and decouple the seat back from the metal structure of the car.
I literally climbed into the trunk to get all the measurements, angles, and so on so I could get available volume calculated, make my initial design sketch, get on the Term-Pro and start modeling the enclosure.
The final design led me to around a 2:1 ratio (2 cubes in the vented side for every 1 cube on the sealed side) with a port of 160in^2 tuned to 58Hz.
With the space I had available (and, more importantly, the amount of trunk I was willing to give up) I built the vented side with an internal volume of about 6ft^3 and 3ft^3 on the sealed side.
This still didn't give me the ratio I wanted for this build (3:1) so I used an old article from Tom Nousaine that absolutely works and used polyfill to get an effective vented enclosure volume of 9ft^3.
A 3:1 ratio has less bandwidth and a higher peak output. Not good for SQ. Fortunately transfer function helps out and I have the processing to tame the peak for SQ.
Since I plan to compete MECA BOBOS (SPL and SQ) I wanted to have the ability to have a higher ratio enclosure that I could revert back to a lower ratio (2:1) by simply removing the polyfill if I choose to do so later. Easy.
The design of the enclosure also gives me the ability to change ports. That way I can run longer ports and tune to a lower frequency or change ports to keep the same tuned frequency if I add or remove polyfill and change the effective enclosure volume of the vented side. The 160in^2 port area ensures that I'll never have chuffing from the column of air that'll be moving through the rear deck.
When I started this I planned on getting the two 15s up and running immediately but life dictated otherwise. As a result the first competition with the car was done after night of thrashing to get the horns/mids in and powered with a JL HD900/5 and, at 6am, I threw together a 1ft^3 sealed enclosure for an Audiofrog GB12D2, put about 1/2hr of tuning on it, and hit the road. At the time half of the 4th order was in the car, the 900/5 was on a MDF plate, and the GB12 enclosure was free to roam around the trunk as much as all the excess cabling, backpacks, chairs, and such would allow.
Everyone LOVED the car. Folks that would get in for a demo would spend 20-30 minutes in the car at a time. It was crazy. In my head I knew the crap that was piled into the trunk but there was something about it that everyone absolutely loved.
I had a judge compliment me on how well the 4th order blended in with the fronts when he came out of the car. Later in the day after awards were handed out I asked him about the car again...and told him there was no 4th order playing. He pointed to the big port in the rear deck.
I opened the trunk and showed him the mess. He shook his head "Just keep doing what you're doing" :lol:
Anyway, here's some photos.
Sitting in the trunk stretched out and making measurements.
Attachment 7900
The main carcass of the vented portion of the enclosure. The odd opening locations are due to the trunk torsion bars/mount locations.
Attachment 7896
My daughter working on the vented section. Installing EZ-LOK inserts so the port can be bolted/unbolted as needed.
Attachment 7897
The sealed section of the enclosure with a mounting flange for the 3/4" acrylic window with EZ-LOK inserts in place.
Attachment 7899
My daughter installing Hushmat's Quiet Tape to the mounting surface of the port flange so it sealed to the enclosure body. I also use this to seal acrylic window to the sealed section.
Attachment 7898