Slotted ports?

I've been seeing more and more boxes with slotted, rectangular ports.  I'm going to be building a new box soon for a single12" and was planning on building this type of port.   Besides looking pretty damn cool, how do they differ from round ports?  Do they sound different?  How do I determine the size of a slot port.  I was planning on building the port out of 1/4-1/2" MDF, is this the proper material?

if your doing SQ, go sealed.  sealed boxes are the  way most professional competitors go when they do SQ.  you have a broader frequency response range and you can use a much smaller box. besides that judges don't like a lot of bass when they judge SQ.  the only reason some people go vented is because every 3 DB over 130 is a free point in SQ, because when you do SQ you also have to run your car on the meter. 

square, circle, and slotted ports all have the same sound, the only use for different ones is box volume and tuning frequency.  before you build your box be sure you know what frequency you sub can play to because many subs that are entry level will blow themselves apart if they go to low. 

Hi all. I'm loocking for 2 new subs. I have two kicker L7 12's going sealed and my God, they are loud but they dont play well low frequencies. I want to sell them and move to sound quality. What subs you people think I should get. Any brand but not above 150 bucks.