SPL Subs
Basket material. Generally more massive due to larger motor structures and coil diameters to deal with the extra power.

Again bigger coils to handle power

SPL subs are probably MORE efficient in the low frequencies than a lighter coned "SQ" sub.


SQ subs usually have less Le, shorting rings and other methods to help reduce distortion.

An SPL sub can sound great. It's more a factor of enclosure than subwoofer in the end that determines the sound quality.

 

IMO the main difference is how they tune, and sometimes that is not that much different. With a real SPL sub when I model it 50Hz peaks and it does not like to be tuned differently. A lot of subs will tune to various frequency so they can be used for whatever. Other issues are the SPL sub will be built to take a lot of power and may suffer things SQ would not like such as (the above) bad FR, higher inductance from a huge VC, lower sensitivity maybe, peaky response, poor specs for linearity, more likely to be physically huge, etc. SPL means burp at 50Hz so the sub would be optimized to do that, rather than play flat down to 30 or 20Hz for SQ and not worry about taking 2Kw without smoking. But subs are getting better and some like a lot of loud in their SQ, so some expensive subs can take a lot of power and still be tuned to work well for SQ. Most of the time enclosure tuning has far more effect than the sub itself.

 

Actually missed your post before adding my own. I agree with this. I only included Le, but there are other factors. Again, like you said, most can still be overcome with good enclosure design.

 

I would say the largest factor is Le (Inductance). If Le is too high, the speaker will roll-off early and won't blend with the front stage well. They also don't likely spend as much time trying to reduce distortion, but that isn't as big a concern for two reasons:

1.) We are less sensitive to distortion as frequency goes down.
2.) If you run multiple woofers, excursion is reduced, and so is distortion.

I agree with the previous post that said SQ vs. SPL is more a function of box design. In fact, I like a low Qts/Qtc, and subs that are designed to be ported have that usually so getting an "SPL" based sub/subs (one with low Le), in the right box can sound quite good IMHO. Another avantage to the beefy basket some SPL subs have is that it can help reduce driver born resonance (another form of distortion).