How many cubic feet do I need?

Just a FYI on how you can decide on sealed vs. vented for any given woofer:  find out the EBP (a number) by using Fs (resonant frequency) and Qes (electrical Q).  The equation is Fs / Qes = EBP.  An EBP of 50 and under is best sealed, higher numbers in the 70's and above are best vented.  But you can work it out either way (with trade-offs) if the number falls between 50 and 90.

ex. Fs- 38.10   Qes- 0.40  = EBP of 95 which says this example needs to be ported.

stevdart,

when using the equation you posted, what are the trade-offs of using a woofer in an enclosure different from what the EBP is telling you? (ex an EBP 50 sub in a vented enclosure). Does it have to do with performance of the sub (SPL or SQ) or can you damage your sub?

chris, you can always damage your sub by using a vented enclosure if set up without safeguards (subsonic filter, incorrect volume of box/port, etc.).  With that out of the way, to answer your question as best as I can....no, you won't do any harm.  In what I've seen, if a subwoofer's EBP calls for a sealed box it means that the sub will respond well to the lowest frequencies that are useable without needing the help of venting.  Whereas, a woofer that calls for venting just won't perform well if placed in a sealed box, generally losing a lot of low-end extension.  50 is on the line between the two, and I would look at it in WinISD if it were me to see which way would be more workable in the particular car.  Going vented normally means the box will be a lot larger, and with a low EBP such as 50, the port size might have to be unreasonably large.  I would only be guessing if I were to try to figure out what differences there would be in the quality, if any, but I know that the overall volume sizes would be much larger in the vented box.

I'm just a newbie, though.  I know some of the information but not all the reasons why.   ;#)

Yes you're right.  The only thing I'm worried about is the sub might not be as screw-tight as the first time.  But I'll try it and maybe like you said I might not even hear any difference.  No matter what I still think it's going to be time-well-spent!!  Thanks. 

cigarman- get the parameters from the subwoofer T/S parameters, like the ones shown in this link.  I also recommend a nice free program WinISD Pro to use to put these T/S parameters into and work up a nice enclosure before you build.  Play around with the program enough to get familiar with it and it will become a valuable friend...although in the beginning it seems difficult (to everyone, it seems, including me).  In WinISD, you'll see the EBP come up in the center of the dialogue box and you'll notice how the program chooses sealed vs. vented according to the parameters.  DYohn posted the equation info on this forum some time back and I made a note of it.  I just pass it along...

MonXing- use some speaker sealant caulk each time you remove the woofer and it'll be air tight no matter how many times you take it out.  I use this sealant caulk but you can also use butyl rubber compound or even plumber's putty.  You can also put a dab of wood filler in the screw holes before re-tightening.

You're kewl, STevDart.  Thanks a lot!!