tuning a box i'm confused

I've got a cerwin-vega stroker and the online manual says to build an enclosure 2.25 cuft tuned to 40 hz. Well I emailed the company to ask if they had tested the sub in other enclosures and how well they did. They told me the sub performed it's best in a vented enclosure 2.39 cuft tuned to 28hz. What I'm confused about is the manual says the frequency response is from 40hz-200hz, so why would they recomend me to tune it to 28hz? Isn't that out of the speakers range?

right, but if the customer service guy tells me to tune it one way, the manual say's different, and then an online manual says something different, which one do I go by?

Can you link to everything you are talking about?

sorry, I should have posted them the first go around.  This is for the stroker 122. Thanks for the help!

http://www.cerwinvegamobile.com/manuals/mobile/cv_mobile_brochure0506.pdf  (page 3)

http://www.cerwinvegamobile.com/manuals/mobile/strokercutsheet.pdf  (page 1)

http://www.cerwinvegamobile.com/CVM_enclosures.html

and the serivice rep sent me an email saying to build the enclosure 2.3927cuft @ 28 hz. he also said the port sould be 4" diameter and 18.125" long. Every single one of these figures are different and I'm lost.

Um.

Okay - I'm going to save the technical explanation and just tell you - if you have specific questions post back -

These are basically the same enclosure - the 40hz tune will produce a more peaky response, and I HIGHLY recommend you go with the 28hz tune - but the box size itself will not make much acoustical impact here - the tune of the port is what is critical here - the speaker box size less so - but keep it above 2cft.

This is a long port - go with about 13 - 15" and you'll remain within a few hz of the target tune - maybe 33hz or so.  I've been playing with boxes this size all day in WinISD for another project I'm working on ...  otherwise the box recommendation looks right on to me.

Uhh - no.  The tune is designed to make the response curve as flat as possible - as such this low tune impacts the response curve, not that particular frequency - what that tune does is lower the remainder of the curve to a flatter response.  This is good.

Well - these maybe different numbers - but the acoustical result, as I've said, will be largely the same.  Just keep the tune below 35hz, okay!

I disagree.

This sort of tune will produce a box that will be very quiet through the majority of the bandpass - only electronica or 35 - 45hz from bass CD's would play - shure teeth rattlingly loud but boxes with a tune this high are for competition where they play a frequency burst - not music - not a 40hz port - this is just too high - no matter what the goals.