let me start out by saying if you cant find jl products for under msrp, in most cases you might be able to do better with other products. ive been in the car audio field for 15 years and have used many brands of subwoffers, among my favorites are kicker, pioneer, ma audio, alpine, mb quart.
ive owned/have a few jl woffers as well. if your looking for spl, want people to here you 3 blocks away and want to blow out windows, jl is most likely not going to make you happy.
i recentely purchased a 10w7 for well under msrp so this was a big + for me. to be fair in "real world" testing, i tried diffrent boxes,sealed and ported and diffrent tuning for the ported.
for the sealed box i used a 1.3cuft, 1cuft, and also the recomended 1.25 cuft. each of these gave good results for me with the 1.25cuft giving the best over all sq. if i were to use this w7 in a seald box, i would use it in a 1.125cuft filled with poly fill to suit my taste.
now here is where i wasted a lot of money, i built 4 diffrent boxes. when the testing was done, i found that 1.6 cuft was the best air space and tuning around 34hz worked best and gave better results than the recomended enclosure. also i found that the recomended port sise (1.5" wide) was not enough. there was too much air noise. re-tuning the box with a 1.75" wide port fixed this problem and added a little more out put vs. the 1.5"wide port.
i powered this sub with the jl 5001 that a friend let me use and it sounded excelent. this however was not enough power so i broke out my 81000d which at 3 ohms is 750 rms at 12.5v and at 14.4v 995 watts rms.(bench comfirmed by landis tech) and still this 10w7 will still take a little more power. i do not compete in spl with this sub but it did give me over 138 db in a 93 cutlass with the rear deck cut out of it. i have all mb quart q series mids and highs in the car and using this sub now for over a year, i have won 4 first place, 2 second and 5 3rd place in local sq contest one of which (first place) was an iasca event at a local soundadvice.
for you "bass heads" this sub with the power iam sending it hits harder than just about ANY single 10" i have ever used in 15 years of car audio
for the sq guys that operate at high power levels, this is the BEST sounding single 10" sub i have used to date.
if you can pick one of these up for under 450$ they are worth every bit