So, I built myself a cheap box of sorts. I forgot to take pics during the build, so please bear with my description.

It started as just a top plate with the subs and amp mounted to them. It shook too much and didnt sound nearly as good as the single 12" in the sealed box, so I went to remedy that.

I added lower sides (left and right near the spare tire and glovebox) and a bottom along with a middle brace to stop the flexing. Sounds great now. Yeah its not anywhere near optimal and I know if I put 2 more pieces of wood on it I will have a sealed box and it will sound better, but Im actually pretty happy with how it sounds right now.



Its nothing fancy and didnt cost me anything as I used some scrap birch plywood I had in the garage. So far total cost of my entire system has been about $750 and thats headunit, rear speakers, amp, subs, and wiring kit.

 

it looks good, but if those subs were not meant for a freeair type enclosure you're going to end up damaging the subs. You should really reconsider building a proper box for them. They'll sound so much better too.

You could even fiberglass a box like I did, and it will be much lighter than building one out of MDF.

 

cdoyle, after quite a bit of thinking and whatnot, I decided not to take the easy way out. Tonight I put on the front and rear pieces and closed in the box. Its not 100% sealed as there were a few small gaps (1/16th of an inch or so) and there are the holes for the wiring to run through, but for the most part its pretty closed up now. I tried to be smart about it and ran some liquid nails around most of the gaps and didnt run it hard after I put it back in the car. Tomorrow will be the test after the adhesive has a chance to setup.

I wish I were a better craftsman as there wouldnt be any gap issues, but oh well, guess its better than nothing. Worst case is I have to scrap it and buy one of those ebay boxes instead.

 

I am extremely frustrated right now. Got in this morning for my commute to work and decided to test it out. It went from nice and deep with no distortion to insanely tight and distorted. I think the box volume is too small for 2 12's. It literally sounds like the bass has gone up a 1/2 octave. I played the same 3 songs that I listen to all the time which have a variety of different types of bass, Bass Can You Hear Me - Beat Dominator, Harlem Shake, and Put On - Young Jeezy. Harlem Shake went from shaking the car to barely audible, like the sound waves are cancelling out. Beat Dominator and Put On are decent, but not hitting nearly as low as they did.

Im thinking I am going to end up scrapping this project and just buy a premade box. Im obviously better at mechanical things than I am at woodworking.

 

Make sure you didn't accidentally wire one of the subs backwards to the amp, opposite of the other one. This will cause the sound waves to cancel each other out because the sound waves will be 180* out of phase with each other.

 

That was actually the first thing I checked. I took some measurements and did some math, the box was actually about 1/2 of the minimum for each sub, so waaaaay too small inside. I pulled the two added boards back off and it went back to sounding nice and deep again. Im not even close to overdriving the subs so Im not overly concerned with them cooking themselves or hyper extending the voice coils in the "free air" setup. They are each rated for 200rms and Im feeding them 125 each. My stereo is also never turned up past 3/4 volume as thats where it starts distorting.

 

Your box looks pretty good, and matches the interior well also. You should really consider sealing up your box. The setup you have in your car is pretty good as far as subwoofers go, plus your running two 12" subwoofers. However, since your box isn't properly sealed nor ported you are missing out on alot of its performance. It is similiar to having a built V8 motor that is running on 4 cylinders; it might get you around, but your missing out on all the fun.

Also I know it sounds simple, but check your positive and ground terminals, a finicky connection could very well be the culprit.

Good luck with your build, and let me know if you have any questions, I would be more than happy to assist you.

 

I really appreciate the advice, but trust me when I say it was really muted when it was sealed and has gained quite a lot of bottom end. I triple checked all the connections as I thought I may have tugged on the ground too much, but its solid.

Since you build custom boxes, you already know the dimensions I am working with, but they way I built this, it wasnt going all the way to the bottom of the well. It is going across from "shelf" to "shelf" without dipping down into that lower portion of the well. I calculated the interior volume to be about 1.486 cuft total for the whole box. Each sub wants 1.375 cu ft, so its a good size for a single but not a double.

I am going to look at it again and see how I can change it up to take advantage of the bottom section to gain some extra volume. Heres a link to a crude drawing of what I have built so far...


The front is tight up against the carpet in the hatch. The side walls also touch the rear plastic trim covering the taillights. Its a really snug fit. I know snug doesnt equal sealed, but its not like there are huge 1/2" gaps either.

 

Haha, I apologize, I just realized I missed post 3 where you stated you sealed the box for the most part. If your box is relatively air tight then disregard my last post.

Your airspace is most likely the problem then. At 1.375 cu ft that puts you at about .65 per subwoofer. A little less than that if you then subtract the MDF thickness of the box. That is territory for a 8-10" subwoofer. For a box that small with a 12" subwoofer, that brings back my V8 running on 4 cylinders analogy.

You should go ahead and make the box bigger to get that extra volume like you said. That should really give you the bass you are looking for.

Again good luck!

 

It's funny because with this current setup, it defies normal car audio logic on how it's working, but it is working. The bass can hit low enough that my wife says it almost hurts. Im chalking this up to one of those unexplainable things where everything is done wrong but yet it somehow works, sort of like my '82 Trans Am. Someone before me put a 2bbl carb on it and stripped off the crossfire injection, but left the stock CC distributor. I was told by MANY people on here that the car couldnt possibly run right without a vacuum advance. I put one on it and it didnt run at all. Swapped the original dist back in and it ran like a champ. No one could explain why it ran and swore I was lying for the most part. This is just another example of something going against what people say should or shouldnt be possible.

Like I said, eventually I will buy a pre-built box, but for now, its hitting hard and sounds clean enough for me.

 

I know what you mean.

I once had a '92 RS with a 12" MTX Terminator 8 ohm sub on a board in the back that I put over the bottom of the rear storage well. All I did was cut it to fit, then cut another board and screwed it vertically on the back to follow the taper of the well.

That setup pounded. AAMOF, With that MTX sub and a Rockford Punch 100DSM, I hit 135.5dB using an AudioControl SPL meter with the mic on the standard windshield placement (IIRC, 12" from the side of the "A" pillar, 4"" from the dash, or something like that).

The best part....
Later, after I blew the MTX, I replaced it with a Pioneer IMPP and I ported it, too. LOL
I don't know if it was louder, but it sure seemed like it.

 

I didn't realize you weren't utilizing the lower section of the storage well. Ya you don't have enough air space for 2 subs.

You should think about fiber glassing a box, that's what I did and it's so much lighter and easier to remove. Plus I can't believe how good it sounds with my 2 IDQ's.

 

How do you go about attaching the top plate to the rest of the box? My wood top plate is a good fit and I'd hate to scrap it. I understand how to mold the bottom portion and whatnot, but am getting hung up on how the top would attach securely.

 

I just fiberglassed the top plate, onto the bottom mold with multiple layers of mat. It seems to be pretty strong.

 

Oh I should also mention I have a top 'cover' that goes over the box. The part you see that is carpeted is removable. The subs are not mounted to that piece, under that is a MDF top plate.