Long time lurker, first-time poster. I am doing this on behalf of all other nervous 1st-time DIYers. Over the last weekend, I just put together a subwoofer that was easy, cheap, and sounds outstanding for my mid-size room. I used the following:
1/2 sheet of 3/4" MDF--$15
1 13" tall, 18" diameter sonotube.--$5
Driver--Elemental Designs e3.8--$40
Cheap wooden dowel rod, cut into sections for legs--$2
3" PVC, found at home depot--$4
I modeled the sub in WinISD. My design goals for this were to be cheap, low, and relatively small. I do not need it to go super loud, since I never listen to my home theater at reference. Nevertheless, this can reach 100db at 25Hz, if the amp is driven to the full 70 watts.
The cabinet size is between 1.45-1.5 cubic feet, and I used 22" of PVC (elbow joint within the tube), resulting in a tuning frequency of 23Hz. I highly doubt I will need anything lower than that.
My endcaps were simply glued on with the gorilla glue, which held and expanded to seal off any air. Just follow the instructions on the bottle and you will be fine. Make sure, when applying the glue, that you either clamp or use heavy objects for clamping (I used my law school textbooks)
This thing is AWESOME. Even my wife, who knows very little about audio, said, "wow, that sub really clears up the low end." What's better, it doubles as an end-table. I will have pictures and the WinISD graph in my next post. All in all, it was very easy, took 2 days (including glue curing time), and was well worth the effort. I now understand why people say that DIY is the way to go.