Audio Systems: good specs for free-air use, aes journal, mazda miata

Question
Thank you for the very fast responce.  The exact aplication is the rear deck of a mazda miata using the trunk as the "box" so it's basically an IB (not a great one but its closer to an IB than a sealed or ported box that's for sure)
A while ago I wrote to a speaker manufac. about weather their drivers would be good for this situation and he said that a sub with low BL (force factor) is good for IB, a sub with high BL will be too controlled in the lowwer freq. and will need a parametric EQ to boost it. This doesnt make alot of sense to me and I guess that's why I'm here.
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Followup To

Question -
I was wondering if you knew what small/thiele parameters make a sub more suitable for free-air (infinite baffel) use?
QTS, VAS, FS, BL, XMAX, etc.

Basically if you could provide ranges or calculations that suggest a sub would have good responce for IB.  thats what I'm looking for, thanks!

Answer -
Richard Small and Neville Thiele are good friends of mine; unfortunately, neither of them ever actually designed a loudspeaker system prior to their theoretical analysis.  Subsequently, they are both great engineers and recipients of many scientific awards for their good work in creating this design and synthesis analysis technique.

NOW: For an infinite baffle (which is a theoretical impossibility in reality) the only two things you need really worry about are FS (free air resonant frequency) and XMAX.  In the IB condition the driver is essentially not loaded so the acoustic mass and such do not change when mounted.  So, the FS will determine the low frequency f3 and the XMAX will tell you how much spl you can get out of it.

But, if you want to delve more deeply, you can go to the original papers published in the AES journal back in the 1980s.

http://www.the12volt.com/caraudio/boxes1.asp   
may be of interest to you.

Hope this helps,
Cleggsan

PS: If you are thinking closed box as opposed to vented box, that is a completely different question, so let me know.  If you are thinking vehicular applications, that makes a difference, also, because they are really not infinite baffle but a pressurized room situation.  Infinite baffle is when the driver is mounted on a very large flat plane with the driver at the center.  

Answer
See my second note with a URL at the bottom. It gives some examples of various parameters for a 12 inch woofer in IB, closed box and vented box.

In my experience the automobile is not a very good representation of IB.  The reason is because of the relatively small cubic space inside the car.  Particularly in comparison with a living room environment.  The car makes the space being radiated into a large, but still small enclosure on the front side of the speaker while the trunk or other smaller space is on the back side of the woofer; thereby making it a dual closed, but large, box design.  There are not good studies on this to give guidance. It is more a trial and error approach.