Split coil Fi? Sexiness!

[audioholic 5,000+ posts]

So is differential drive topology also isobaric? Is it semantics to say this is not isobaric because it does not utilize the coupling of two separate cones, or is it semantics to say its isobaric because the basic idea of opposing forces are used? I believe you could call this an isobaric motor topology if you want to, but to suggest this is no different than the traditional isobaric design, as your question implied Kyle, is misleading at best. In the end, what its called IS semantics, but its not semantical to point out the differences between this design type and the tradition dual cone, dual speaker, isobaric setup that halves Vas.

 

[jimrhit 10+ year member]

After a few minutes looking at this ... I'll venture a guess as to what they are doing ..

Dual Gap, diff drive but not exactly the same, since the circuit is more efficient in some respects.

Looks like the center gap is made of the two top plates. If the two magnets are charged reverse of each other (and somehow held together with those seemingly small screws), they would be effectively doubling B in the center gap (relative the just the lower motor alone). The top circuit is a bit less efficient than the bottom given the extra reluctance of an air gap vs back plate, but nonetheless you are getting quite a lot more B (kind of like adding a bucking magnet .. in this case, it is a bucking motor. Looks like the top gap is really 1/2 the length of the lower gap, but the pole extension will make the effective gap a bit bigger, especially with such a large VC OD.

They then use the second gap, similar to how JBL does with diff drive, with a reverse wound coil to take advantage of the gap they needed to create to allow the former to pass through.

The total effect is much more B on the "main" gap, with the second, reverse wound coil taking advantage of the second gap. Overall, you basically have two very high B gaps and two coils. They have canceled out most of the inductance (assuming the windings are the same for each coil) and gotten a lot of motor force in a really deep package.

So, the top coil is reverse wound vs. the lower coil and the mech limits are controlled by electric braking from each coil on the up/down stroke entering the other gap. Super High Xmax, lower turns relative to a multi-layer coil, better HF reproduction/dynamics/speed, easier for amps to drive, (relatively) lower moving mass

Would like to see some real world specs and measurements on this guy .. pretty interesting.

note - this could be 100% wrong, but this is what my mccafe is telling me right now

As far as isobaric, kind of ... you are adding a second (but maybe not doubling like iso, just using up the lost B and adding a elect. brake) motor force to the same diaphragm assembly, lowering qts allowing you to stiffen up the spider and keep a relatively low qts while lowering vas and t/s based enclosure requirements for a given in-box qtc.

 

[Kyle_Keating 10+ year member]

I'm guessing the top motor is like a JBL DD design and there is just an extra normal motor bolted below it.... I'm not even going to go into what is odd about that considering the difference in flux in the gaps and the different gap heights. I would have to see a cad diagram to confirm.

 

[Kyle_Keating 10+ year member]

So is differential drive topology also isobaric? Is it semantics to say this is not isobaric because it does not utilize the coupling of two separate cones, or is it semantics to say its isobaric because the basic idea of opposing forces are used? I believe you could call this an isobaric motor topology if you want to, but to suggest this is no different than the traditional isobaric design, as your question implied Kyle, is misleading at best. In the end, what its called IS semantics, but its not semantical to point out the differences between this design type and the tradition dual cone, dual speaker, isobaric setup that halves Vas.

not really, its still one motor, you just add a second gap, and half the coil cross section area and shrink the gap in half (tigher gap). That is what DD is, and i not saying this design is at all. And of course we dont have to "shrink" the gaps in a DD design, but we'll end up with more coil and moving mass which is untrue to the purpose / design / concept of the JBL motor. (not that there is a right or wrong of course) The total B in the circuit remains the same. You can see here we literally have a second entire motor in the mix. Now its not quite exactly two of the same original gaps, but one can make a claim we now have twice the B and hence the isobaric design from a motor standpoint.

 

[PioneerSPL1990 10+ year member]

wheres a physist when we need one

 

[audioholic 5,000+ posts]

not really, its still one motor, you just add a second gap, and half the coil cross section area and shrink the gap in half (tigher gap). That is what DD is, and i not saying this design is at all. And of course we dont have to "shrink" the gaps in a DD design, but we'll end up with more coil and moving mass which is untrue to the purpose / design / concept of the JBL motor. (not that there is a right or wrong of course) The total B in the circuit remains the same. You can see here we literally have a second entire motor in the mix. Now its not quite exactly two of the same original gaps, but one can make a claim we now have twice the B and hence the isobaric design from a motor standpoint.

You missed my point in mentioning DD I think.

And as I said, you can call it an isobaric motor topology if you want, but your question was what makes this different than traditional isobaric setups. Quite a bit. Original isobaric designs coupled two drivers to alter Vas and lower distortion. This design is certainly different than that traditional isobaric design. Maybe Im reading too much into your original comment of what makes this different than other isobaric setups, as I read it as suggesting this is nothing new. It is.

 

[ciaonzo 5,000+ posts]

After a few minutes looking at this ... I'll venture a guess as to what they are doing ..
Dual Gap, diff drive but not exactly the same, since the circuit is more efficient in some respects.

Looks like the center gap is made of the two top plates. If the two magnets are charged reverse of each other (and somehow held together with those seemingly small screws), they would be effectively doubling B in the center gap (relative the just the lower motor alone). The top circuit is a bit less efficient than the bottom given the extra reluctance of an air gap vs back plate, but nonetheless you are getting quite a lot more B (kind of like adding a bucking magnet .. in this case, it is a bucking motor. Looks like the top gap is really 1/2 the length of the lower gap, but the pole extension will make the effective gap a bit bigger, especially with such a large VC OD.

They then use the second gap, similar to how JBL does with diff drive, with a reverse wound coil to take advantage of the gap they needed to create to allow the former to pass through.

The total effect is much more B on the "main" gap, with the second, reverse wound coil taking advantage of the second gap. Overall, you basically have two very high B gaps and two coils. They have canceled out most of the inductance (assuming the windings are the same for each coil) and gotten a lot of motor force in a really deep package.

So, the top coil is reverse wound vs. the lower coil and the mech limits are controlled by electric braking from each coil on the up/down stroke entering the other gap. Super High Xmax, lower turns relative to a multi-layer coil, better HF reproduction/dynamics/speed, easier for amps to drive, (relatively) lower moving mass

Would like to see some real world specs and measurements on this guy .. pretty interesting.

note - this could be 100% wrong, but this is what my mccafe is telling me right now

As far as isobaric, kind of ... you are adding a second (but maybe not doubling like iso, just using up the lost B and adding a elect. brake) motor force to the same diaphragm assembly, lowering qts allowing you to stiffen up the spider and keep a relatively low qts while lowering vas and t/s based enclosure requirements for a given in-box qtc.

Good insight, thanks for posting all that.

I'm realizing how little I know about differential drive systems and that I really need to gain some experience with these.

 

[jimrhit 10+ year member]

Good insight, thanks for posting all that.I'm realizing how little I know about differential drive systems and that I really need to gain some experience with these.

You're welcome ... I can't say its right but I think it is looking at it a little more now

I have just a bit of diff drive experience //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Yeah Kyle ... the whole design is pretty funky .. but actually kind of neat that they are using the lost/stray B from the typical bucking magnet and taking advantage of the benefits of reverse winding. A lot of asymmetries to worry about and a big freakin fea mess .... but still its kinda cool.

 

[Kyle_Keating 10+ year member]

its actually not lost or stray flux. Lots of stray flux is going to be lost no matter what due to shorting before the gap. In a DD motor, they just slice the return path and create another gap, doest really increase or decrease flux, but you get twice the coupling, so if you add twice the coil, you get ~50% more BL (actually a tad less), if you half the coil (for example, 4 layer to 2 layer) you get about the same BL but you double the surface area of the coil and increase thermal handling - that's why JBL did it, and they ALSO get a region between the coils of flow inductance because the two coils run in opposite directions. In this case, they add a second motor and a second coil, they get a ~100% more BL (give or take, im simplifying it quite a bit) we really should look at concrete examples with curves to get a full understand, but that's beyond what we really need here. That's the best i can do without a drawing, maybe Nick or Scott could chime in.

 

[Jaredturp 10+ year member]

Sorry if this is a repoast of common knowledge, but on SMD (bring on the hate) Steve has just switched his BTL's out for the AA version of this... with AA teaming up with Fi and all that..There are pics, and those things look filthy..

 

[corrie32 10+ year member]

Looks like Fi is taking things to a whole new level.
Split coil...in a whole new definition

http://www.soundsolutionsaudio.com/forum/index.php?/topic/32483-mmmm-split-coils/

looks like the coil in the new SMD sub