10" under dash subwoofer (Page 1/2) 1985 Fiero GT FEB 15, 10:37 PM Starting with a little backstory, 1985 Fiero GT, no AC (smaller air box), I've already upgraded the dash speakers with Rodney's 2 way speakers, I've upgraded all the headrest speakers with pioneer 4" 2 way speakers, and I got a "Dual 10 inch powered subwoofer" from Walmart. It was small enough to fit behind the passenger seat, but being tall, and from a tall family, I decided it pushed the seat too far forward, so I was going to build a larger, thinner enclosure for behind the seat. I then decided, out of curiosity, to look under my dash by the air box, and see if I had space under there, and much to my surprise, with a very... Specifically... shaped box, it would theoretically fit. So then I made a calculation to see if there was enough total volume for the subwoofer, the original Walmart enclosure was 820 cubic inches, my calculation on total available under dash space was 1100 cubic inches. With that, I started measuring, drawing, cutting, glueing, repeat. Took the dash out and reinstalled a few times, each time getting better and better. The end result was a very oddly shaped box, made up of 18 pieces of plywood, then painted, then partially covered with the carpet stripped off the Walmart enclosure. New box volume is somewhere between 800 and 860 cubic inches, but due to the impossible shape, hard to calculate. As you can see, the subwoofer is as big as it can possibly be, and the integrated amplifier board is screwed into the side, just as in the original from Walmart. Walmart original: After these pictures, I installed it, and it didn't quite fit, it pushed the dash out a little too far, so today I removed it all again and trimmed the upper portion (that was hitting the passenger vent tube running across the dash), didn't affect the actual subwoofer mounting, but I just finished reinstalling everything, and it fits perfectly. To mount the subwoofer, I have it strapped to some of the standoffs on the frame of the car (for holding cables, etc.), and it is very tightly fit between the dash and the firewall. I had to relocate the blue dingy thingy along with the horn relay and hazard flasher and I zip tied it above the gas pedal, way up above the firewall front compartment electrical pass through, still audible and accessable, but out of the way. Final result is a straight dashboard, nothing behind the seat, and way more bass then I need (only have the 10" because it was on sale, for $50 Canadian) I have it turned down to a reasonable level, and can further control it via the eq on my radio. It sticks down about 1-2 inches from the bottom of the dash (air box sticks down 3-4 inches, so from the perspective of the passenger, it is invisible, the speaker itself is directly above the passenger dead pedal, but as long as they don't kick up, there's room for size 12+ feet, so should be fine, sound is very well distributed, much better then from behind passenger seat, no rattles, etc. I don't have pictures of it in the car installed yet, as I finished at 10 pm, to dark and cold. But it fits perfectly, and while the enclosure is absolutely horrible to build, it took a whole tube of pl premium max to seal all the gaps between the pieces forming that complex curve, then some silicone caulking to seal around the actual sub and the amp board. Total cost was 1/4 sheet of plywood (already had it, so free for me) 1 tube of pl premium max (again, already had it, so free), and half a tube of silicone sealant (free again), and the subwoofer that I bought in the first place, $50cad. Total cost to buy would be around $40cad material+subwoofer and amp, and a lot of hours of work. This will NOT work on cars with AC, as the air box extends a few more inches into the free space, and due to the shape, 10" will not fit in an AC car, but 8" probably will and 6.5" will. Also with some of the complex curved space taken up, an enclosure for cars with AC, or non AC cars that just want a smaller sub, would much more closely resemble a simple box, and be easier to make. 1985 Fiero GT FEB 16, 11:00 AM New pictures fully installed: Passenger POV: Seat height POV: Other angles: 1985 Fiero GT FEB 18, 06:27 PM So has anyone else gotten a 10" sub to fit under the stock (no AC) dash. I know I had searched for pre built alternatives before, and as far as I know generally the largest that had been put under there is an 8", even then it is tight, most people who have done large subwoofer builds also have AC, which is why basically every site that talks about aftermarket subwoofers says 6 1/2 or 8" is the biggest possible. Anyone else use a 10" in that location, anyone else use plywood and pl premium max to construct a box? I am certainly not a bass enthusiast, and would have probably found the factory sub adequate, but for 50 dollars and some labor, it was too good to not get. I don't know whether this thread will be helpful to anyone who is an audio enthusiast, but it is something I haven't seen anyone do before. Cliff Pennock FEB 19, 11:27 AM That actually looks pretty damn good! I have the stock subwoofer (well, not completely stock since I replaced the subwoofer which was broken with an aftermarket one) and although music sounds better than without subwoofer, it can't really keep up with modern (house) music. Bass gets distorted really fast if I play a nice techno stomper. 😁 1985 Fiero GT FEB 19, 11:28 AM quote Originally posted by Cliff Pennock: That actually looks pretty damn good! I have the stock subwoofer (well, not completely stock since I replaced the subwoofer which was broken with an aftermarket one) and although music sounds better than without subwoofer, it can't really keep up with modern (house) music. Bass gets distorted really fast if I play a nice techno stomper. 😁 Yeah, this is much bigger then I need haha, but for 50 dollars, I can't complain, it does mean there is basically no distortion until it is much louder then I'll ever want! Formula FEB 22, 10:48 AM That might be the best sub install I've seen in a Fiero. Good Job! 1985 Fiero GT FEB 22, 11:25 AM quote Originally posted by Formula: That might be the best sub install I've seen in a Fiero. Good Job! Thank you very much, it was a crazy idea that I had! A_Lonely_Potato FEB 24, 06:26 PM definitely put a grate of some kind over that cone unless you want a passenger foot going through it 1985 Fiero GT FEB 24, 06:27 PM quote Originally posted by A_Lonely_Potato: definitely put a grate of some kind over that cone unless you want a passenger foot going through it Yeah, I'll be looking into doing that, before the car comes out of hibernation. 1985 Fiero GT FEB 24, 06:44 PM The other thing is it is very high up, about 1" above where the carpet ends, I've been in and out a few times and it is no problem, unless they intentionally kick up. I think the factory subwoofer sticks farther down then mine does!