Well i put 15 and subwoofer to be descriptive but its the legendary tempest and only comes in one size.
I ordered this sub for a friend and a profile CL600 and bridged it to 2 ohms (not recommended by profile but i did it anyway)
My first impressions when I saw the sub i was like man... this thing is small but it wasnt for me and it looked like a good deal for $125 so i was gonna go with everybodys opinion on this.
We spent about 6 hours building the box and trying to get the massive thing in the car (took out the back seats) and after we put up all the tools we were set.
I wasnt expecting much from it because i have a 12" xxx but he played some music he had in ahead of time and it was pretty **** loud. I went inside and made a cd and we went right down the road to eq the system. I set the gains right and turned the bass all the way down on the hu so it wouldnt distort his stock speakers and started playing some music. I put in nothins free by lil jon and the eastside boys and i was amazed at how loud this thing got. the lows were also amazing. Next i played thug walkin by yin yang twins and this thing put out some earth shaking low bass. I continued to play some more songs and I was more and more impressed with it.

Heres the setup
some low line kenwood hu
stock door speakers
Adire Tempest in a 4.5 cu ft box tuned to 24 hz
Profile CL600
no sound deadening
Mercury Mystique

Bang for the buck factor really plays in here. the sub is on sale at www.visionaryaudio.com for 125 shipped until december 26th. I got the amp for 102.99 on thezeb doing a price match off of ikesound.
built the box for about 30 bucks
so all in all it costed 260 and he has an awesome setup.

if you are a fan of LOW bass and have lots of space, i say do 2 of em
This sub is one of the best ways to spend $125