The Type-X is a rather unique subwoofer design that is optimized for a very specific purpose and application. If you understand the design and what it excels at (and consequently what it lacks), it's performance, in-car frequency response, and output capability makes a lot more sense.
It's a great niche subwoofer for those who recognize what it can and cannot do, and implement accordingly. Unfortunately most people purchase or audition the Type-X with the preconceived notion that it is a performance upgrade of the Type-R subwoofer. This is partially the fault of Alpine marketing department, and partially because it is significantly more expensive than the Type-R. (and partially because people do not know how to analyze and utilize T/S parameters). At any rate, this is incorrect.
So what is the Type-X optimized for? It's a high Qts/Qes driver design (weak motor), high Mms/Mmd (very heavy moving mass), moderate Fs, low EBP, low SPL sensitivity. This all points to a driver that is optimized for sealed box use. Enclosure size requirements are moderate. (Not outrageous, but not exactly small for a 12" driver). Anechoic F3 in a medium sized sealed enclosure is extremely low, lowest I have ever seen in a 12" driver, especially for car audio use.
Remember, Hoffman's Iron Law dictates that a loudspeaker can possess (or rather, be optimized for or excel at) any two of the following three properties, but at the expense of the third property:
1) Small box requirement
2) SPL efficiency
3) low-end sensitivity and extension
For example, if a driver was designed to work in a small enclosure and have relatively high SPL efficiency per watt of input power, low-end sensitivity and extension would be greatly reduced or compromised as a result.
Back to the Type-X. The driver clearly has low SPL efficiency. It's basically 83dB for the 2007 12" model. It doesn't exactly have small box requirements either, however it is still rather small for this type of driver design.
So far we have deduced that the driver has extremely poor SPL efficiency, and good/fair small box requirement. That only leaves.... {drumroll please}.....
Yup, you guessed it, low-end sensitivity and extension. And that, my friends, is what this driver excels at. It has EXTREME low-end sensitivity and extension in only a moderate sized sealed enclosure. Couple that with in-car transfer function (cabin gain) and you have one of the sickest low bass capable 12" subwoofers to ever grace the car audio market.
It adds up on paper, and it adds up in my trunk. (I bought two of them //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif )
But as I mentioned before, it's an unorthodox design that has only a niche appeal IMO. I feel that most people prefer a driver that will work equally well in sealed and ported boxes, and most people prefer a driver that has a higher SPL efficiency and smaller box requirements, at the expense of low-end extension and sensitivity. This is actually the general category that most car audio subwoofers fit into. Quite the opposite of the Type-X.
Another thing I want to mention is that for the most part a driver that is extremely low-end sensitive like the Type-X usually lacks on the top-end without an extremely versatile EQ and significant tuning. Such a driver design will probably require an unusually robust midbass setup to compensate, and/or an unusually advanced and capable outboard processor. Most people do not possess this.
That makes this one of the more difficult subwoofers to work with and implement and tune properly. Definitely not for the average user who just wants to drop it in and go, or just wants some loud bass in the trunk.
The Type-X is supposedly a lower distortion driver than the Type-R, but to my knowledge Alpine hasn't released the technical data to confirm this. I would like to think that it is given the price difference, but I cannot verify. It's definitely well built and well designed, and offers plenty of mechanical and thermal power handling. (which is always relative, I know. this isn't a "super woofer")
I hope this helps to clear up some (common) misconceptions regarding the Type-X subwoofer.