There are many SQ subs that can put out some bump. Such as the IDMAX. Most SQ subs can't compete with an SPL sub in output. SQ subs are designed with sound quality in mind. They have a very even and accurate response.
no it does not it is a sub it is just geared to sound better than to get super loud it still can get loud but its not really ment for it have you ever heard a w6v2 or idmax
a sub designed for SQ is meant to be very accurate and clean sounding, usually when you design a sub for SQ you sacrifice some ability to get loud like other subs designed pure loudness. oh, and all subs are speakers. subs are big speakers meant to play low frequencies.
a good SQ sub is one that has very good and accurate sound while still being a sub. it doesn't get muddy when playing intense bass sections and it won't over emphasize the bass. I think alot of what it comes down to which is hard to tell from the specs is how good the magnetic fields are on the sub. How quickly it has control over the sub movement is a major factor on SQ for a sub.