Half the Vas, and half the Xmax of any of the other drivers we've looked at.
Frankly, nothing works well free air. That's why we try to seal doors as best as possible. People use egg crate foam behind the speaker to absorb backwaves, and all other sorts of voodoo that either help or don't.
We (as in car audio) look for drivers with high Qts numbers as a sort of baseline for how well the driver will react with large volumes of air, or free air. This doesn't always tell the best story, and can be sort of voodoo as well. The car door does absolutely no favors to any driver. The smaller the driver though, the harder to get decent midbass performance because of the large volume of air. With even a sealed door it is quite large. So, in essence the guy at Madisound is correct. However, suggesting a driver with half the Xmax, and half the Vas doesn't bode well either. It's not a driver that will provide a decent amount of midbass. It may act very controlled within it's usable bandwidth, but there's nothing it can do that the L15 can't do as well. What we're hoping for here is a bit more performance.
The L15 has a higher Qts, and almost double the Xmax, and Vas. You won't get everything the L15 has to offer, but you can get more out of it.
I can throw even more drivers into the equation. Vifa PL14 is a great driver. Detailed, with a very smooth, velvety sound to it. Great upper end extenstion, with good off axis performance. Should provide some decent midbass as well. Low Fs, decent Vas, and Xmax, but lower Qts have made me skip over this driver. Doesn't mean it won't do well, and it could possibly do spectacular, but it's a punt.
Speaking of punting, just about anything will be a punt. There is no way to tell how any driver will react once installed in a car door.
We're trying to work within the parameters of the vehicle without carving out door frames, a-pillars, and any other panels that may get in the way. It's a challenge, and frankly why I'm addicted to this hobby over home audio.
The Seas Neo is a great tweeter. So is the MDT12. The LPG is spectacular at what it does. The Dayton ND20 is a superb little performer for the money. The L15RLY is a great driver. So is the CA15, and the Vifa PL14. I'm willing to bet the AC130 will be nice as well. Peerless makes some great drivers, but nothing I'm willing to stamp for this particular application. If I had to pick a Peerless I'd pick this one.
http://www.madisound.com/cgi-bin/index.cgi?cart_id=3904266.20886&pid=1953
Nothing is going to sound as good in the car as it would in a properly built enclosure for any given driver, including anything "designed" for car audio. So, when the guy at Madisound says the L15 doesn't react well free-air, I hope he's not comparing apples to oranges. He may be correct, but there's a difference between, "this will explode if you try this free air", and "you won't get full potential out of this driver".
I can make an argument for this driver as well.
http://www.madisound.com/cgi-bin/index.cgi?cart_id=8248629.18658&pid=1074
Let's be realistic about what we're trying to accomplish here. We're trying to take a well engineered piece of equipment, and put it in one of the most harsh environments we can dish out, and expect it to perform to a high standard. Same thing as asking a Porsche 911 to do 140 mph on a road riddled with speed bumps and potholes. Something's gotta give.
It's hard to stand back and say this will work and this won't when I know for a fact that unless I'm there with a stockpile of drivers next to you to test, anything will be a punt. I really enjoy spending other people's money, but I have some integrity as to feeling really, really bad if something doesn't work out. So to that end, I try my best to find the best fit for a given application. Madisound is doing the same thing. They have a lot more to lose though if you're an unsatisfied customer. So, I think they're playing it a bit more safe when they make recommendations. Unrealistic expectations can kill a relationship, and Madisound definitely doesn't want to do that.
In the end, it comes down to effort. The more you put into treating the doors, and giving the drivers the most controlled environment possible the better the performance. 80% install, 20% equipment. This is why Dynamat, and Ensolite exist. This is why DIYers like myself go to great lengths trying things like shoving modeling clay all around a baffle, and using egg crate foam behind a speaker, and anything else we may think will help. Some of it's voodoo, some of it actually helps.
