I have some issues with foam. Perhaps there are different formulations out there now, but my experience tells me the following:
1) Foam rots. I am really tired of throwing away woofers that are still fine in every other respect, but the foam surround has turned to dust. I have numerous drivers (dating back to the late 70's) with rubber surrounds, and they are still going strong. This is especially a concern for outdoor speakers.
2) Foam surrounds generate noise. I have heard this demonstrated, and there is an amazing amount of mid and hf noise generated by those things. It is not a harmonic, so it won't show up in harmonic distortion analysis. Just poor S/N.
3) Foam is unstable with time. I hate when my woofer parameters change after the cabinet is built.
4) As far as I can tell, foam surrounds are simply a cost cutting measure. Last check foam surrounds were about 10% of the cost of a decent rubber surround. It tells me that the manufacturer is cutting cost. Sort of like buying a high performance car and finding that it has the cheapest tires that they could find, and they are welded in place so that you can't change them! Worse yet if they are foam tires.
As far as alignments go, I could have made a lot more racket with these with a bass reflex or PR alignment. Since damping and transient response were a criteria, I ruled those out. Indoors the woofers are faster than the room, so it isn't a big issue. Outdoors, however, there is no room reinforcement or overhang. It is amazing to hear deep bass that can start and stop like that.
Making loud bass at 40 hz is pretty easy. Getting accurate bass at reasonable levels outdoors at 20 hz is a tougher challenge. Try it, it is fun!
One other point of note: I chose the woofer that I did for performance to cost ratio. I have no intention of setting $1000 worth of drivers outdoors to get rained on. My satellites I can stow indoors, but the subs need to be weatherized.
If I had it to do over again (and I do) I would go with a sealed alignment and equalize for flat response. This would yield a smaller cabinet, and pretty similar results. I just wanted to try a bandpass design. It does protect the woofer nicely, but now I have to design against critter intrusion (the things are natural bee hives).
Sigh...time to get back to my real job.
gerG