The only piece of my system I wasn't as content with as the others was the sub. Don't get me wrong the PDR10 is a great little sub for its' price range, but it just always seemed to be straining during movie action sequences. So the question became what should I get to replace it. Started looking around and posting to forums. Considering I'm in Canada I was seriously considering the Paradigm PW2200 which would have cost me between $900 and $950 CDN after taxes. Then in my posts on AVS this loud mouth arrogant guy :p with a ridiculous number of posts informed me that I should build my own sub (by the way thanks Bob). It would cost half the PW2200 and blow it away. Needless to say I was skeptical, but he and some others pointed me to "The Sonotube Links Page" and the DIY forums on www.hometheaterforum.com and www.hometheatertalk.com. I then went through a couple weeks of reading and coming up with different design ideas, all the while asking a lot of annoying questions on the two above forums.
It was pretty easy to decide on either a Shiva or a Tempest (Adire Audio) considering the number of people on the forums using them, their low cost, and the ability to use LspCAD for free to design an enclosure using them. I was initially going to build a sub with as small of a box as I could. So I was considering an isobaric design using two Shivas. I eventually decided that would be too complex and costly to try. The long port lengths (which could have been solved by passive radiators at even greater cost) and cost of two drivers just didn't make any sense for me. I then decided, why not just make a bigger box and use a single Shiva. I was going to go with the Adire EBS alignment for the Shiva, using slightly modified dimensions with an AVA250. Helped by my readings on the forums enlightening me to the virtues of big subs, I then saw the light again and decided what the hell, the Tempest is only $20 USD more, why not use it. I was still wanting a box, but this time I decided I'd make the box as big as would fit where I was going to put it. I came up with what would have been about a 150L net box tuned to 17.5 Hz with a single flared 4" port. All looked good and I ordered the driver, amp and flared port kit. At the time I was pissed off, but luckily the AVA250 was on backorder (as it turned out for a month and a half). Over this agonizing waiting period I eventually came to the conclusion that if I'm going to build this thing, I should do it as close to right as I could the first time. My limiting factor is the foot print, not height, if I stuck it into the corner of my room. So with a Tempest I could get a rather small foot print if I used an 18" diameter Sonotube and just make it stupid tall in order to give the Tempest the volume it deserves.
Having learnt a lot on the forums along with my driver and amp finally shipping (I cancelled the 4" flared port kit). I had decided on my final design:
However, as Dr. Hyre of Adire Audio pointed out this design introduced one possible problem. The length the sonotube would need to be in order to get 260L would be the same as a half wave length of a 90-110hz sound wave (5' to 6' tube). There would be the possibility of standing waves forming in my tube. He also suggested that if I put about a foot of insulation around the port is shouldn't be a problem. As it would turn out he was correct. Go figure :p