fiberglass box space?

So I finally got around to finishing one of the two single sealed boxes for my 12" JL Audio 12W0's. So my question is as follows, I wanted to see how it sounded in the box I made. I measured and I figured I am about .3 cubed feet under the reccomended space so I don't think it would have that big of an effect. So I put one of the speakers in the fiberglass boxes and the other is in free space. Hooked up in parallel I turn the system on and it sounds weak. The bass isn't anywhere near like I remember it. So I figure I need to compare it to the factory sealed box that came with the 2 12" 12W0's. So I put that in there and I connect everything up and it sounds MUCH better. So I was wondering after I complete the second fibgerglass box, can I expect the same amount of bass or am I just gonna be let down? It is also a possibility that I had the speakers wired wrong and they were only getting half power. I haven't checked that out yet, I was just wondering from the experts at the12volt.

...assuming the amp was at the same settings (gain, LPF, ect.).  Did you by any chance stuff the box with poly-fil?  Give it a shot...1lb. of filling per 1 cu. in...retry with that....let us know.

It's pretty tough to give you any real advice if you don't know if your equipment is hooked up correctly. I'm assuming you are compensating in your mind for the fact that you basically have one sub running, is that right? and the sound you're hearing is about half as loud as the two in the factory box. Running a sub free air isn't going to do much of anything. To see what I mean you can try hooking up just one sub free air ( careful you can damage subs this way) and you'll hear that it's real weak and unsupported. Also what is the volume of the box you were going for. .3 is nothing for 8 cubic foot box but if you have a 1 cubic foot box it becomes a big deal. try torquehead's advice with the polyfil, you can also use batting or insulation. i'm assuming he meant per cubic foot.

Oops, ya got me GrantD!!!  Ive been building a few engines between other fabs, so Im stuck in Cubic Inches.  So, definately Carbonb, its Cubic Foot for air volume in this case! ....my bad!  1 pound of polyfill per 1 cubic foot of internal volume.  IF your really in trouble, a little more.  If your in really - really - really bad trouble, build another box.  If your crafty with your planning, and totally dependant on your box's location, you can possible hid an additional pocket containing that 0.3 cubic foot your missing.  Ive had to do it, its not that bad of a deal.  Keep us informed!!!

Well the requirements for the sub in a sealed enclosure is 1.5 cubic feet. I haven't actually measured my box, I basically just used measurements to try and guess. I don't have any packing peanuts so I am going to try and get some so I can measure and be precise about it. Until then I think I am roughly around 1.1 cubic feet so I am missing about .2 cubic feet for the sealed enclosure. However, the reason I don't think the equipment was setup right is because I was running 2 speakers in parallel. The first time I didn't pay attention to the negative and positive terminals on the subs. So, basically I had the negative positive switched for one of the speakers when running in parallel. Not sure if that would make a difference. I see your point with the freespace sub, so I am not going to know until I make the second box and test both subs. Also I didn't have polyfil in my fiberglass box, but the factory box has polyfil in it ;P So, that could be another reason for it's performance over the 1 free space and 1 in the fiberglass box. I'll finish the other box and give yall an update and post some pictures up as well. Show my amp rack and fiberglass box, I bought black carpet to carpet them, but my trunk carpet is a mid to dark grey and it's a big contrast :P Hopefully at night it won't apppear to be a big difference.

If you have already finished all the fiberglass work on the one enclosure the packing peanuts aren't going to give as much useful information as it would've prefiberglass state as you have to do a lot more work to change it, although you still can. I'm not sure I completely follow your wiring mistake but i'm willing to bet it makes a pretty big difference. does your prefab box have a divider between the two air chambers? sometimes they do. In which case you could do an apples to apples comparison running one sub. The ultimate test to whether the volume is big enough is going to be your ear and whether you think it sounds good enough. Keep us updated. -Grant D

Yeah Carbonb, when you wire in parallel, keep the positive wires from both speakers together as well as the negatives together when wiring to the amp.  It will make a difference, it keeps them in phase.  Also, if you are that far off from the required air volume, you will be able to tell the difference regardless....whether or not you use polyfill, however, it always helps.