Originally Posted by Marcus Gan
I recently bought the JTR S1 and my 2 old 10" sub cannot integrate with the 18". So decided to off load the 10" sub and build another 18" seal sub to place at the back of the room to smooth out the FR.
I'm assuming your 10" subs were ported? That would explain integration issues with a sealed sub, especially since the tuning frequency of the 10's was probably in the range of 30-35hz, causing phase issues with the S1 below that frequency.
If your goal is just to smooth the FR, the 5400 is probably overkill.
These two 18" drivers are very popular now days, and are very capable given their low price point:
Dayton RSS460HO-4 18": http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-472
Stereo Integrity 18" D2: http://stereointegrity.com/index.php?id=60
Put either of those in a 4-4.5.cu.ft sealed box and it should have no issues integrating with the S1.
What amp are you going to use?