Bought one of these for Pro Audio, arena and outdoor use, who wouldn't want to be known for the biggest subwoofer front stage at every event?
Its a show sub, your not going to throw away your 18s or your 21s since you will most likely see better spl out of them around 50hz to 100hz. However where this thing shines is under 50hz, I personally have it cut at 60hz with a wide open bottom, however it sounds fine to 500ish "if" you wanted to use it in a 3-way system with 500hz/2500hz cut. It boasts 14hz, but I think thats just where it starts rolling off, as I have hit it with 5hz-20hz waves and felt the vibrations/seen the speaker move quite a bit.
If you dont already have a stupidly large setup and are looking for some ultra low end bass, your better off spending the cash on some 400w 18s or 1000w 21s, you'll get 3-6 of them (or more if its just drivers) for the price of this.
only negative/good thing (aside of the price) would be the funky dual input voice coil. For a Pro audio user, this is a very weird 2 coils at 2ohm rating and a large pull from two inputs. So basicly you need a stupidly powerful amp, 2x 2500@2ohm RMS or 2x 5000w@2ohm peak (like my crown ma9000I) Bridged amps are 4ohm, so you cant use two bridged amps, it must be one amp unbridged. The nice thing about 2ohm is it does actually pull ALL of the power off a channel of an amp, so one solid amp needs to be paired with this. Again the price of this amp is going to be more then if you power 400w 18s, you could find a amp to power 2ohm 1600w = 4x18 400w/ea, doubled (8x 18xs) in one amp for around 1/5th of the cost of a high end amp like my crown ma9000I.
Unrivaled and Unforgetable, perfect if you need a memorable center subwoofer. If you need actual sound, at this hefty price, unless you only want visually "the best", then you may find a better bang for your buck in lower wattage equipment. If you can aford, its worth it and people will not forget it when they see it, that alone is worth more then the value of this speaker, if you can aford it again and your serious about what your doing.