Here ya go....................
SDP of TC Sounds fame had this to say:
"In a vehicle, a sealed enclosure will ALWAYS best a vented enclosure for low frequency extension. Always.
Most sealed woofer systems start rolling off at 50Hz or so. With the 12dB rolloff below system resonance, and the transfer function of the vehicle - the average end result is a woofer system that extends down below 10Hz flat.
With a vented system, below vent resonance, rolloff is 24dB/oct. In a vehicle, most vented systems exhibit an exaggeration in response from 30-60Hz (average). This exaggerated response at 30Hz, is usually what is considered 'deep' or 'low'. With the steeper rolloff of the vented system, 10Hz stuff will be virtually in-audible and non-existent.
To go low the 'real' way - a sealed woofer system is the ticket.
If you're concerned with output 30Hz and above - a vented system is the way to go.
Many advantages and disadvantages to each option. But to settle the arguement on which kind of enclosure goes lowest - sealed is the answer.