[Bill Fagal]

Board seems kind of dead, so I thought I'd have some fun with a little speculation.

Anyone besides me still intrigued with Adire's XBL2 technology? Now that XBL2 drivers have been shipping for some time, they won't mind if we indulge in a little reverse engineering, will they?

So for the sake of public edification, anyone willing to take their Brahma/Tumult down to their local metalshop and bandsaw the motor in half so we can see a cross section? Didn't think so.

Well, short of that, here's a sketch of my guess at the innards of a Tumult XBL2 motor. The brilliance of this topology is how the voice coil traverses between two gaps, with special attention paid to keeping the fringing fields symmetrical and the VC winding hight optimized for a constant BL over the transition.

http://image1ex.villagephotos.com/pu...sp?id_=2297319

Any thoughts?

If I have some time over lunch, I'll try to do a quick finite element model of the field density distribution and post it.

Bill

(Edit: Switched to a link to save bandwidth.)

[Seth_L]

Bill,

I think you have too much free time at your job.

Seth

[Bill Fagal]

Shhhhh... I think my boss might have heard you. :wink:

[Bill Fagal]

Alright, here's a finite element flux density plot. I roughly modeled the outer dimensions based on the info on Adire's website. I specd 1006 steel pole/top-plate and grade-8 ceramic magnets. (I don't know if they use grade-8 or 5, so I gave them the benefit of the doubt--certainly enough to saturate the pole.)

I'm just guessing at the top-plate geometry, but a really scooped-out channel between the gaps seems to model best, and saves weight to boot.

Take the actual values with a grain of salt since there are so many unknown variables (like, for example, whether or not this is actually XBL2 at all. )

http://image1ex.villagephotos.com/pu...sp?id_=2299011

Notice the symmetry of the fringing fields and negligible flux between the gaps. I believe these are crucial to the design to keep BL constant from inward VC excursion, across the gap crossover zone, and through outward excursion.

These twin gaps allow the VC to completely traverse a magnetic gap with each half cycle, shortening the winding hight necessary to achieve a given excursion. Brilliant!

I don't know if anyone else out there has any interest in this stuff, but driver design is what I do for fun, so I find this line of conjecture facinating.

Bill

Edit: Switched to a link--bandwidth, ya know..

[Steven Kephart]

Actually I've been involved in a speculation discussion similar to this that spanned two forums. Maybe our thoughts might give you more information. Here's the links:
http://www.teamamp.com/ibf/index.php...t=5344&hl=xbl2
We continued the discussion on Acoustic Visions's forum in the car audio section. Unfortunately it's not there anymore, so it must have been erased. Maybe we were closer than we thought.

[Bill Fagal]

Interesting link, Steven--Thanks!

The link back to this forum was especially enlightening. I hadn't seen that discussion before.

Quote:

We continued the discussion on Acoustic Visions's forum in the car audio section. Unfortunately it's not there anymore, so it must have been erased. Maybe we were closer than we thought.

Perhaps so. Well, I'm not out to steal Adire's lunch. I first arrived at my abovementioned conclusions almost a year ago while the Tumult specs were getting hashed out on this forum (my first visits here). I enjoyed the challenge of trying to turn the scattered clues into a topology that matched published dimensional and performance specs, and I believe I succeeded.

I've been sitting on this idea since then, not wanting to be a thorn in Adire's side. Of couse, by now I expect that all the industry types who have reason to be curious have already thoroughly disected XBL2 motors, so I feel my speculations won't cause harm.

Of course, if this thread disappears, I guess I'll have some idea of why!

Bill

[Kyle Richardson]

It wasnt deleted! I think this was the discussion you were thinking of Steven.

[Steven Kephart]

Thanks Kyle, that was exactly it. I looked throught that section several times and couldn't find it. How odd. Thanks again for the help. I really appreciate it.

[Ryan Schnacke]

I don't think Adire will consider this kind of discussion as threatening. They know that once the patent is approved then it will be made available for anyone and everyone to read. And their rights are already fairly protected since the patent is pending.

[Bill Fagal]

Since I think XBL2 relies on twin gaps, each used for 1/2 a cycle, The design makes less efficient use of the combined field strength than a garden-variety overhung motor (wasting the flux lost across whatever gap doesn't have VC windings in it at a given excursion point). Of course, this is a necessary compromise to extend Xmag with a relatively short coil.

This would seem to mean that, to keep efficiency up, they'd want to spec a big magnet.

In my FEA output, notice that the polepiece seems to be the flux bottleneck, reaching saturation first, (unless the gaps are shorter/narrower than I specd, which they very well could be).

Looking into my crystal ball, I'm thinking the next XBL2 extreme sub may feature a 4" VC. Fattening the pole piece from 3" to 4" seems an obvious step if you want to boost the max total flux in the motor to allow for even more Xmag at a given efficiency.

Another nice thing about XBL2's short coil is that they can probably move from a 3" to a 4" VC without getting giant Le numbers.

One downside of a new 4" XBL2 super-excursion motor: It'll probably weigh more than your little brother!

Chubbiness is pretty much an unavoidable fact if you want to carry a lot of flux a long way through a magnetic return circuit. I'm working on a concept driver with a 70mm Xmag, and just the steel in the magnetic circuit calculates to about 80lbs--and that's largely flux-saturated!

Anyway, It'll be fun to see where Adire takes XBL2 from here. But remember--you heard the 4" VC prediction here first!

Bill

[eric]

i had a look at what the xbl2 motor looks like from one that got destroyed and was taken apart (spider, former, and cone removed). i dont clearly recall what it looks like tho--and if i did, i wouldnt be able to disclose it anyhow...i dont know about how flux flows or any of that stuff, and i would have loved to have seen a 1/2 brahma, but it didnt happen.

anyhow, my idea was a sort of dual gap design (this was before seeing the brahma gutted), tho it was contoured instead of being squared off as you suggest. the biggest problem from how i pictured it was that it would requite magnets above and below the tp (did i mention i dont understand flux ).

eric