Soon to be 4 Sp4 18s on 2 Ia 40.1s, Just waiting on the other subs to be shipped, until then a quick video 

 

http://youtu.be/ZjusaPtV1ZI

 

Nice! Thats some good flex. How do the sp4's play? Do they pretty much play most frequencies well or are they more of a 'low and loud" kinda sub? Most subs I've had just dig low but drop off higher than 50 hertz. I'm thinking about a couple of these also. Sorry to jack the spotlight. Awesome vid should be nasty when you get those other two!