Most bass guitar cabinets lack the ability to go deep - even ported, but sealing a cabinet does hinder the low frequency extension even more.
When you ask about cabinets, and which ones go deep, it has nothing to do with the magnet on the back of the speaker. The Physics of loudspeaker cabinets give you a 3 way tradeoff at low frequencies - extension, size, and efficiency - the smaller and more efficient you make a cabinet, the less low frequency extension you have. The tradeoff most companies make is they do small, they do loud, but they don't do deep, because the first two are seen as more important then the deep part.
As people started making neodymium cabinets, they were also making them smaller - if you want light, you gotta take away wood, because the magnet isn't all the weight. So yes, the Neo cabs of today have less "deep" ability than the ceramic mag cabinets of yesteryear, but it has NOTHING to do with the magnet material - the don't go as deep because they're smaller. In this case, size does matter (as well as efficiency). If you want to get REALLY picky about it, a neo driver technically helps you get a tiny bit more extension, because in any given size box, there is less magnet, so there can be more air (the box is bigger inside). Are you gonna hear that tiny difference? No, but if there is a edge to neo or ceramic magnets in terms of deep, the edge, however miniscule , goes to neo.
If you want to see the bass cabinets that go the deepest, look at Acme. What makes them go lower? They give up efficiency - it's the same tradeoff, but they have chosen low frequency extension over efficiency.
If you want deep and loud, you get a bunch of Acme 8 ohm cabinets (the 112 edge wound one, for example), and you array them. Individually, they are as efficient as one of the original drivers on an Ampeg 810 (which is to say, not very efficient at all), but if you array a bunch of them (what the Ampeg 810 does), you gain back efficiency due to the array gain.
