Good Subwoofer recommendations


I'm looking for a good Sub for my existing HT system.

There are so many types like Sealed, Ported, Cylinder, Bass-reflex, etc. & it's a bit confusing to determine which one will be better. Also, does type of speakers or Amps I have can impact the decision?

My budget is around $1000 & I prefer getting a used or refurbished rather than new.

Current setup:
LRC Speakers: Tyler Acoustics Linbrook System II
Surround Speakers: JBL S312
Amplifier: Parasound Halo A51
BD Player (cum PreAmp): Oppo BDP-105
Room: 16x18+ with ~40% open walls, so sound can bleed

Thank you in advance!
hitsofmisses
Thanks for all your suggestions. I ended up buying my friend's 10 years old SVS 20-39PC Plus.

It's not as high-end & versatile as some of the models suggested here but it does the job fairly well at a fraction of the cost ($250). It's 40" tall & has custom-built 12-inch woofer with a 525 watt power amplifier.

Except of it's physical appearance, during playback you'll hardly notice it is even there while still providing fuller & richer sound.

Thank you once again!
Is sub primarily going to be for music or HT? if for music I go with REL and not look back. REL is tight, fast and musical. good with HT but not great, unless you go with their higher offerings. I just ordered two REL t9's which houses two 10inch drivers and should fit the bill for my room and should do pretty well with HT.
I had Tyler custom-fabricate a really nice subwoofer for me two years ago. Fits the bill perfectly, and the finish matches my Woodmeres.

PSA xs15se 15 inch sealed down fire, excellent for ht and music. I think they are about 750 brand new and delivered.
There is a Vandersteen V2w here for $950 that would be my choice. I have the audio-only version (2Wq) which has been a terrific performer--fast, tuneful and integrates well with the speakers.
Rhythmik and REL make very good subs, as do SVS. However, my favorite subs are the Velodyne DD and Optimum series - these are *fantastic* subs...

http://velodyne.com/subwoofers.html

-RW-
Check out SVS. They are a great company. 45 day return policy with free shipping. I had the SB-1000 and it was outstanding.
Rythmik has their E15HP in matte black on sale right now for $1024 plus shipping. 15" Servo-Feedback woofer, 600w amp. Best deal in subwoofers.
I think SVC makes great lower cost subs. A critical question, though, is if you are just going to be doing movies or will this be your TT/CD/SACD system as well? If you want it to do everything, I strongly recommend a sealed set of subs. Ported subs are just too slow, unless you want to do some serious modification. In my HT room I'm using a set of sealed subs and have found it a fair trade off to the one ported sub that is found in so many rooms. I do have a 15" sub in the garage/gym that is ported, but even there I had to modify the port and use a lot of Marigo speaker dots to get it to be listenable. I have to say, though, exercising to a 15" sub is motivational!
There is a Bag End Infrasub 18 for $895. That sub was a review winner many times for HT. Probably can't go wrong with that. With 40% open walls you will need the size as well.