well for one they put a huge *** aluminum heat sink between the coil and the magnet.
It's really just a shorting ring with fins -- other than being visible and dissipating more heat to the open it's no different than one in a ferrite motor. Inductance will be lowered quite a bit, though. It has no effect on surface area contact of magnet to steel -- simply spacing the magnets out a bit also is insignificant to the overall strength as they are saturating the steel and not the gap directly. The Neo is no farther away than what a big diameter Ferrite slug presents (eg: a common pole size is 74mm OD but magnet doesn't start until 110mm ID on many common slugs).
Based on the spec on their site the BL^2/RE is 296 on the D2 (D1 is essentially identical at 291) BTL-N3 which is pretty close to the 305 I got from a Warden (N3 is 2.9% less) and the 328 from a DD-99z (N3 is 9.7% less). These figures will vary based on the coil used in the motor, of course, as I've gotten varying numbers from Wardens with different coils -- the 305 is most recent.
The variance between all of the big 3" Neo subs BL figure is essentially due to varying gap width / height and the amount of winding in the gap compared to the total winding width (as they all have different coils and top plate heights) and not the position of the magnets -- as all of them saturate a 3" pole within a small % of one another.
The DD-Z does not have a traditional top plate (gap height is simply equal to the Neo height which is ~40mm on the 99z that I had), this is correct, but does have a back plate -- all of the columns do connect directly to a steel plate in the back to transfer flux from the pole. As the magnets are charged horizontally the flux just goes directly to the pole rather than through a top plate (the top plate looking piece is just aluminum to hold it all together). I don't see any particular advantage to this design other than during assembly... based on the ways I've come up with to assemble a charged Neo unit the way that DD's goes together seems the easiest.
Also note that the MMS goes in the opposite order of motor force; with Fi the lowest, IA in the middle, and DD the heaviest... mass is also a factor in SPL.
So this really all just boils down to one thing -- all of the top 3" Neo drivers on the market have pretty well fully utilized what a 3" core can handle as far as flux despite very different appearances and motor designs.
Your application will determine which one is loudest as they have VERY different soft parts packages on them -- I'd expect SEVERAL dB difference depending on peak frequency, box volume, etc between them all with original soft parts... but if you built them all with identical soft parts there would be a very small difference in SPL.
Just some objective analysis on them all based on my observations //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
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As for the original topic... Fi was huge on here for some time. I believe they are still quite popular -- just not talked about quite as much as it's not "new and exciting" per-se. Plus they also have AA and OEM to work on so it may not be a huge priority to push Fi as much as it once was.
