What is XBL^2?

[buggsson 10+ year member]

http://www.soundsolutionsaudio.com/forum/index.php?showtopic=9421[/url]
I haven't updated it in a bit as I have discovered more about the effects of inductance...and more specifically, inductance variation, but it is for the most part very accurate (in my opinion).

I'm waiting, should be very interesting read

 

[Rashaddd 5,000+ posts]

Good write up DD

 

[SHOemup233 10+ year member]

Most intelligent thread I've read in a long time. Thanks guys.

 

[tez4life Premium Member]

Most intelligent thread I've read in a long time. Thanks guys.

Indeed, thank you as well. Very good write up as well DD.

 

[bose301s 5,000+ posts]

Wow, looking back it is funny how little I used to know //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[Kyle_Keating 10+ year member]

You cut the top plate into a [ shape and the pole into a ] shape. The cut-out area is referred to as the "rebate" -- this rebate steers the flux towards the two separate gaps on either side of itself to extend the BL field out farther to either side than a motor without the rebate. This creates a flat BL curve and thus less BL distortion and more linear x-max.
Some people get the idea that XBL^2 actually loses BL, but it really does not, it steers it around... in some motors I've drawn up in FEA I was able to get a higher BL with XBL^2 than with other "standard" topologies. Even in motors where the "at rest" BL is a bit lower, the average BL over the useful range of the speaker will be higher.

Jacbo, You're 100% right about "it steers" it around, i think you meant to say "B" not BL, and yes, it conserves the flux lines, but it also couples with 50% less lines in the total gaps so............in my calculations (i wrote software to do this using FEA motors i designed) i was not able to get more "BL" from any XBL^2 model i measured. in fact, i have a hypothesis that any linear motor must sacrifice BL... worded a little differently of course.

my models of XBL^2 include two solutions that are pretty convincing. I FEA'ed three motors. An overhung, and then two XBL^2 motors. One with 50% shorter and 50% lighter coil and one with 50% shorter coil with double the turns (same mass and resistance the overhung)

The results are as follows: the first XBL^2 motor has aprox an 27% BL(0) loss. Very large! the second had about a 9% BL(0) loss. Both gap widths were corrected for each coil. The first xbl^2 model used the same gap as the overhung (say # of layers on the coil) the second XBL^2 motor has a larger gap for the larger coil. the second model was much better in terms of coupling but still lower that our overhung, and the inductance of the system exceeded that of the overhung because of the extra coil in the gaps. Sure you can put a shorting ring in the notch in the gaps on either side, but you can do the same for an overhung coil with an undercut t-yoke which is basically what the XBL^2 t-yoke is. putting a shorting ring directly in the active GAP and winding it is going to reduces sensitivity the same for either XBL^2 or overhung, its a wash.

about the linear stuff, sure, the overhung has higher BL, but its still a non-linear method, the XBL^2 is a linear method, so there is the trade off. XBL^2 has lower distortion. But XBL^2 also has a difficult time correct for asymmetry about the x axis. variable coil solutions can in fact easily correct for this without having to use a very high extended poll piece. I have found that most XBL^2 motors i have modeled have higher xmax on the down-stroke. This can be corrected with a carefully designed motor im assuming.

my point is, Dan W. is misleading about his accusations according to my analysis and im out to correct the record. I have debated this with him before and i will be publishing an extensive paper on this at some point. I'm not the only one to come up with this conclusion too. Steve Moray (former Bose engineer) did similar research completely independent of me and found nearly the exact same results.

http://www.s-m-audio.com/topologies.pdf

his model included a "well hung" motor which is simialr to a DD design or a 3HP /4HP motor

 

[Kyle_Keating 10+ year member]

BL linearity is there but BL is still lost. Not only are you taking steel out of the motor, but you are intentionally taking B out of the area that the coil is located the most....right where it straddles.
But the only linear BL approach that I know of that does not have some efficiency trade-offs is MMAG.

I would aruge MMAG does...

MMAG is hard to compare with, but if we think of it just like a dual gap design, two gaps and a coil that splits them both, you still have the same problems as XBL^2... loosing 50% of the active coupling. Its not the notch in the gap that reduces efficiceny in XLB^2, its the fact that the coil doest ever catch more than 50% of the total gaps... implying you have high flux density that remains uncoupled by a voice coil at all displacements. Neil, as you know, the same can be said about LMS, you have less L in the gap.... so there is a loss.

In terms of MMAG, the orientation of the magnets should not matter that much unless its a more efficient way of getting flux from a magnet. Aura manged to do this at the expense of complexity with their radial design for example. I'm not sure MMAG carries the same value, it would take some careful analysis to determine how much more efficiency is gained from dividing up the magnet like that.

 

[newusername 10+ year member]

I would aruge MMAG does...
MMAG is hard to compare with, but if we think of it just like a dual gap design, two gaps and a coil that splits them both, you still have the same problems as XBL^2... loosing 50% of the active coupling. Its not the notch in the gap that reduces efficiceny in XLB^2, its the fact that the coil doest ever catch more than 50% of the total gaps... implying you have high flux density that remains uncoupled by a voice coil at all displacements. Neil, as you know, the same can be said about LMS, you have less L in the gap.... so there is a loss.

In terms of MMAG, the orientation of the magnets should not matter that much unless its a more efficient way of getting flux from a magnet. Aura manged to do this at the expense of complexity with their radial design for example. I'm not sure MMAG carries the same value, it would take some careful analysis to determine how much more efficiency is gained from dividing up the magnet like that.

Yes, MMAG does sacrifice efficiency. At the time of the post, I was misinterpreting an aspect of MMAG implementation. So my remarks require revision:

All topologies that target improved BL linearity accept decreased efficiency.

Wow, looking back it is funny how little I used to know //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I think the same thing every day, but that's how it is supposed to be: no man is born with all he needs to know.

 

[ngsm13 5,000+ posts]

Neil, I miss you.

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nG

 

[bose301s 5,000+ posts]

Neil, I miss you.
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nG

x2

 

[James Bang 5,000+ posts]

we miss the klippel tests //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

 

[Earthman 10+ year member]

I love technology //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[James Bang 5,000+ posts]

 

[bose301s 5,000+ posts]

we miss the klippel tests //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

Hopefully they will be getting that sorted out soon.

 

[v2.0]

Wow, looking back it is funny how little I used to know //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I find it funny how little you still know.