hsvgtsr1 said:
What details do you need?
Vented or closed designs only need the Thiele-Small parameters. These are the resonant frequency, equivalent volume, and 'Q' of the speaker. The rated impedance will affect the low pass filter design. All of these values are available from the manufacturer of any modern driver. You can also measure them yourself with fairly primitive equipment, but it would be rather involved for a one-off project. Any of the above mentioned box design programs will then spit out appropriate vent sizes, depending on your choice of box size. The response of the system is absolutely determined by a fairly simple mathematical formula involving these parameters. However, it is still somewhat 'black magic' due to the variability of the parameters, electronics, and environment, and also due to the subjective nature of the perceived quality.
Steve, the impedance response is very peaky and frequency dependant, but fortunately, the coupling efficiency at resonance offsets the main peak, and a fairly smooth 'response' of a bass driver usually results in a gradual dropoff at higher frequencies. The trick is to extend the maximum smooth response on the bottom end. This can be done as you mentioned by either punching up the amplifier response, equilization, or by using active second (or greater) order filters. This is what has sparked the revolution in tiny subwoofer design. By offsetting the naturally poor low end response of a small box, with both the low-end punch from the reflex vent, and the electronic boost of an active filter, you can squeeze a lot of sound out of a tiny volume.
Mosfet, you are right that a tuned column will far outperform a vented box in loudness. This is great for cars and boats where you want to thump the crap out of music and blow a few windshields out. But hsv mentioned a home theater system, where you probably are better off concentrating on even response, and rattling the windows is actually a negative consequence. Tuned columns sound crappy in a closed room where the natural resonances of the room interact with the 'tuned' frequency. I am not trying to be a purist here, either. I could care less whether the music is faithfully reproduced, I just want the maximum thump for the buck, too, with the least amount of rattle.
One way of getting that sub-audio shake is to use vibrating transducers attached to the floor (or, perferrably each seat). A little spendy, but cheaper and smaller than corner horns.