According to Dan the lack of the shifting BL keeps the sub with a consant overall q which doesn't occur in typical designs which have a rising q as excursion increases. Perhaps that was the issue you had with the xxx? Suspension noise might be the other issue, I know my AA avalanche had some noise before 27mm although you couldn't hear it from inside the car.
And Dan is correct. With typical overhung motor topologies your Qt/Qe rises as BL drops with increased stroke. Take a look at any BL plot on a typical overhung design vs. an XBL^2 design, which you can see in
this comparison. Any drop, rise, variance of BL directly effects the Qt/Qe of the system...which also effects the Qtc of a sealed alignment and the volume required for a vented alignment. Let alone suspension variances and how they effect the overall performance. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
The other major issue I can see being the issue on a xxx is flux modulation.
Flux modulation itself was kept within limits, as keeping flux modulation constant in the gap (where it counts) is what XBL^2 is famous for. In its day, the RE XXX was a very formidable driver capable of very high linear displacement which no other driver at the time was capable of. If anything was to fault in that design it was the suspension and/or basket limitations.
They used a pretty big coil on those and took no attempts at keeping the inductance down, which is why they dont' play anything over 60hz very well at all. Regardless when we look at things in the current domain, the XXX probably isn't as pretty as it looks on paper. The newer model shiva and tempest x's both use faraday rings to keep inductance and inductance variation with stroke even.
The XXX did what it did the best, and that's handle the most amount of power while keeping BL related distortion to a minimum. Inductance variation and linearity wasn't a concern when the XXX was initially built because the people who were using the driver were using it from 60 Hz on down with little to no regard as to how well the driver 'disappeared' when put into SQ competitions. Complaining about the latter would be like complaining that an Aston Martin doesn't get 40 mpg while going to the grocery store. But even then, this is opening up a huge can of worms because you'll find people all over the place that prefer the sound of higher inductance drivers to lower inductance drivers because they offer the degree/kind of distortion they are accustomed to (yes, I said it //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif), irregardless of what they see and understand from the data. I'll be the first to admit that true low distortion, in all aspects, takes some getting used to.
The Siva-X and Tempest-X both use shorting rings to tame inductance from a measurement and linearity standpoint, but they also handle considerably less power than the older model XXX did. Everything with loudspeaker design is all about give and take. The newer Exodus offerings are great for HT applications where low and linear inductance is preferred. In most car audio applications for the XXX (especially this forum), low and linear inductance isn't as crucial as what numbers it puts up in the SPL lanes.
The motors are also dead quiet under full excursion or so I've been told. Since you like playing with subs tuan, why not try a more updated XBL^2 design?
That they are. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Dead quiet while played free-air, as all good sound quality drivers should be.
