Aiyo George the 5% rule!! The Lambda Acoustics SB12 that you brought for me from US was a touch n go scenario and I spent many a nights poring on EXEL spreadsheets trying to find a compromise.
Another basics question a DIY would ask is whether a driver is suitable for sealed or ported box. A simple explanation from The Loudspeaker Design Cookbook by Vance Dickason:
Woofers intended for use in closed-box systems are characterised by low free-air resonance (fs), relatively high cone mass, and long voice coils.... In terms of driver Qts, closed-box loudspeakers generally require woofers with a fairly high Qts of greater than 0.3... R.Small suggested a good rule-of-thumb which he called Efficiency Bandwidth Product (EBP)
EBP is quantified by:
EBP = Resonance Frequency / Driver Electrical Q
EBP = fs / Qes
EBP in the vicinity of 50 or less indicates a sealed enclosure would be more suitable, while EBPs of about 100 suggest a vented enclosure.
As an example the Lambda Acoustics 12 driver is suitable for sealed box. Why?
From the SB12 T/S specs:
F s= 20.9 hz
Qes = 0.64
EBP = 20.9/064 = 32.2, which is below the thumb rule factor of 50
Thus the SB12 is suitable for a sealed box and indeed its makers suggest cabinet of 2.0~4.0 cubic feet sealed.