general box build

Well, I had elaborate plans to use 2 corner boxes I pixked up, and re-vamp the system with 2 12's, replacing my current 15. Then I started thinking...Why mess with a good thing? Plus I'd have to find another 2 decent 12's to buy, sinking more money in.

So, I'm back to my old plan. My current box is 3.5 cubes, ported to 34Hz, 36W X 16H X 19D, and was done up on RE Enclosure Calculator about 2 years ago. The box is painted red, looks shabby as hell, hence the reason I'd like to make a new, much cleaner version. I've had a few people tell me that the RE calculator is way off on the specs it gives in terms of the tuning frequency, is this true?

I've been looking at the calculators on this site, and was thinking on building a 3.5 cube box, and using 1 or 2  6" PVC ports with curved edges (Using the old heat up the puipe and press on a metal bowl trick) The calc tells me for 33Hz in the 3.5cubes, and 1 6" port, I'd need 15" for lenth. So I have a few questions here:

• In telling the calc 3.5 cubes, I assume that means after sub displacement? 
• With 3.5 cubes, is that after port displacement as well?
• Instead putting 1 15" port in there with an elbow on it (I was thinking I'd make the depth 15" this time around, so I'd need an elbow to get to 15") could I put 2 6" ports with 7.5" lenth each?
• Ethier way, will that 15" of 6" port provide me with enough port area so I don't get port noise? I know 16 per cube is usually good, and I can calculate it for a slot port, but what area am I looking for in a round port?

If anyone wants to put something together for me to go by, or just ideas, max dimensions are the same as the old box (36W X 16H X 19D)  However I'd like to cut the depth down a small amount. Shooting for 3.5 cubes @ 33Hz, with enough port area not to give me a ton of port noise.

I look forward to hearing your responses. Thanks in advance for the help, I appreciate it!

I can get 58 sq/in of port area using a 4 inch wide by 14.5 high port, 16 sq/in per foot, which should definatly keep the port noise away.

Another question. I have a large amount of 5/8 mdf in my garage from a small sub box I built in my shed (Local yard only had 5/8). Can I build the box from this, or should I play it safe and go buy some 3/4? Keep in mind it's a 15, seeing 600-800W RMS