OB vs BR: driver excursion
 

I'm wondering if there is any formula or rule of thumb to quantify the difference between the excursion of a full range driver in an OB versus a BR (or sealed) enclosure.

I'm wanting to get an idea of how loud I could play an unfiltered 5" driver in OB before it bottoms out, based on accounts of what others are achieving with that driver in their enclosures. I'm guessing it will depend somewhat on the volume of the enclosure and diameter of the ports?

cheers,

B.

This spreadsheet should help you out

http://www.linkwitzlab.com/spl_max1.xls

The short answer though, is that a 5" in OB will not produce bass at any useful level. OB speakers require shifting a lot of air to produce the low notes and no 5" stands a chance. That's why you see peoples OB rigs with often multiple 12-18" drivers per side.
Play with the spreadsheet and you'll see the difference in air you need to move monopole vs dipole

Thanks.

Should have been a bit clearer. I'll be running dual 15" OB subs per side so only need to get bass down to ±200hz. My concern is only about the possibility of bottoming out the driver. cheers

then just go ahead and run a sim of the driver in a massive closed box, say 5000L and have a look at that excursion plot. It should be the same as the excursion in OB

What on earth are you talking about?! With 50000W applied and a .5Hz signal, the excursion is much higher in the OB!

:D

Seems like a very reasonable recommendation to me. For a first cut you could run the three configurations in one of the freeware codes and get a good idea of the driver deflections as a function of frequency and trade-offs made going with each design. You will not get a good look at the OB driver's SPL response because the baffle roll-off is not included.