Re: watch this stereo vid
I didn't look at the vid, but Stegen, you may be right about a Transmission Line Enclosure. They are mostly used in Large area's like clubs where there is just too much air to move to build pressure. I've seen them built into Stages as well. (2) 32' Woofers in 50 cu ft of enclosure moves serious air. It's really not very impressive though. You will wind up using as much air space, (enclosure volume) as if you put (2) 10' or a 15' sub in your car. You can get roughly the same output, but completely different sound. Since you're using a series of chambers to increase the sound pressure, (the vent acts as an additional woofer, moving a large volume of air) you make sacrifices. In a car, where waves are too long and the woofers are so close to you that there are other things equally as important as pressure. Group Delay, is a measurement of time that gives you an idea of the accuracy of a subwoofer system. With the vent building pressure from the back wave of the cone movement, there is a considerable delay before the development of the note. The speaker moves forward and vibrates air, as the speaker moves back it forces the air in the vent (port) to leave the enclosure. Tuning the vent creates a lower note than what the cone created, giving more output. However; the increased low frequency energy is delayed from and is not in phase with the original signal.
Also don't forget that (2) 6 1/2' speakers are almost a 10' in surface area. About 12 years ago I built a Mazda Navaho with (12) 6 1/2' speakers that were being dicsontinued. The truck did around 146 Db. I don't remember the exact number, but is was lounder than the 27' woofer that was in that truck previously. I still say the best thing for most cars is a Sealed subwoofer system. Use Ported is you want more output and if you can pull it off, Free air gives the best of all worlds with improved accuracy.