I liked the old round ones. great subs for small sealed boxes. I was sad to see those go.
crazy white boy
The new ones kick butt. My friend had 2 15" round ones and I had 1 15" square one and mine sounded way louder. The squares move 20% more air than the rounds and can produce a lower frequency and higher wattage handling
your friend probably had a different amp, car, and box than you, too, and all of that affects SPL. The square L5 and L7 subs have a problem with tinsel lead separation, too. the leads break. the surrounds also fail and come apart prematurely.
I'm just not a big fan of square subs. if you want SPL, get a sub that's round and has a good Xmax.