Anyone Have Experience With These:

edited my post to include math, read above, and don't believe the hype. Im not out to prove one is better than the next, just separate the myths from reality.
I dont know enough about motor structure or function and T/S specs or terminology to separate myth from reality. Oh well. Im working on it though.

But from the looks of it underhung > LMS and XBL^2 for SQ and efficiency.

 
underhung is not very efficient, probably less than both of those, overhung is the most efficient, and from there, the closer to even hung is even more efficient. Underhung works great when you either need a higher Q or you have a really powerful motor.

 
Dan Wiggens has done a good job selling his story about higher sensitivity and lower inductance, but looking at the math we can see that XBLL does linearize the BL, but at the same scarifies that LMS has (and split coil for that matter). It will not beat a straight overhung coil at the same xmax.
Hi Kyle,

There are multiple advantages in terms of a rebate in the gap, especially when you consider placement of shorting rings and counter coils; this isn't just from XBL, but you can see the research of Doug Button, Marcelo Vercelli, Ejvind Skaaning and others with placement of shorting rings and coils. Suffice to say, putting a ring below the gap does not function nearly as well as one IN the gap; likewise, rings above and below still do not function as well since the bulk conductivity of the rings is most likely not balanced.

For example, consider the following measured impedance of midwoofer I designed a few years ago, which uses a 66mm diameter voice coil and a motor design with 18mm one way linear (as measured by a Klippel):

UltraLowZDriver.png


As you can see, there essentially IS no inductance; the bulk inductance is around 15 uH, about in line with the best tweeters out there. And this is for a 66mm diameter voice coil with 18mm one way linear stroke, and one that handles a 700W RMS amplifier all day, every day, in thousands of recording studios around the world. This is a direct result of putting the inductance reduction system IN the gap, rather than outside (which simply does not work as well).

This also is a great benefit from a cooling standpoint as the average position of the voice coil can contain a highly thermally conductive material like aluminum or copper; or, if desired, cross-drilled holes into the center of the gap forcing air over the voice coil itself.

With respect to motor design and its benefits, you're ignoring one of the major ones (and why you can find XBL in many products in different CE segments, including those you can buy in your local Best Buy): motor height. For a given stroke, an XBL motor can be significantly shorter. In general, an XBL motor can be roughly 60% of the height of an overhung and still have the same mechanical clearance. This means magnet stacks can be significantly shorter, and weight greatly reduced as desired. And one can push more of that magnet out in the radial dimension so as to better use the flux available in the magnet, if desired (as you know, for a given amount of magnet, you want to maximize the surface area touching the steel, so as to maximize flux density in the gap - spread your magnet out as much as possible rather than stack it up where you get precious little return in B in the gap).

So when you actually adjust for the same DCR of voice coil, same mechanical clearance, and keep the amount of magnet weight and steel the same (meaning going with a fatter but shorter stack) one will often see significant increases in B field strength - the shift of some magnet from height (for mechanical clearances) to width allows for big gains in B field. A lot of your analysis overlooks this basic benefit to underhung or XBL motors - you assume static magnet shape but that is NOT a static assumption that needs to be made, and in fact is a hindrance to the design of underhung and XBL drivers.

This shorter design for the same mechanical stroke was the primary reason XBL is used in so many conferencing phones from Polycom and others; a taller speaker leads to a taller physical package of the phone which has a measurable degradtion of the PESQ (objective measurement of sound quality) score for the phone, since multipath reflection is increased for the multiple mics. The greatly reduced distortion - relative to equivalently-sized overhung speakers - was a key in selection because THD from nonlinearities is extremely detrimental to echo cancellation techniques. So a low distortion, very shallow driver is essential to proper conference phone design. This is one example that simply cannot be equaled with any overhung (and indeed, both Microsoft and Polycom, independently at different times, spent months looking for a solution before stumbling across XBL and quickly licensing and using it - measurably lower THD in the shallowest package available).

Additionally, gap dimensions do not have to be kept the same; gaps on XBL (and underhung as well) drivers can be tightened because of the shorter voice coil. For a given level of mechanical stroke, and a given precession of the former, the shorter voice coil results in less radial displacement; basically, rocking of the cone will result in less sideways displacement of the voice coil before it touches the top plate or pole, meaning they do not have to be as wide apart as they do with an overhung. And as magnetic flux falls off with the cube of distance, even a small reduction (say 10%) in gap width can result in large gains in B field (28%, for the 10% gap reduction).

Likewise with total coil assembly mass. Because of the shorter voice coil length, the former is shorter and that mass is reduced. I know of no engineer who complains about a lower starting mass! As you know, it's always easy to add moving mass, but often difficult to remove. Having a lower mass means you can gain in total driver sensitivity, or - if you wish to "spend" that mass savings - go to a larger diameter voice coil and slightly larger diameter wire (so as to keep the DCR the same), and that larger diameter voice coil will increase the BL and thermal power handling. This is a tradeoff and option that's available because of the short voice coil of XBL (likewise with underhungs); it's not available with overhung designs. It's not necessary that one uses it, but it's an option at least with this approach.

Additionally, consider the impact of flux modulation under power and with transient bursts into the voice coil. The BL curve is skewed because of saturation effects in the steel from the voice coil. In a typical overhung, you'll find the B field becomes a continuous slope from one side to the other, and the BL curve will mimic that result. However, with an XBL motor the rebate assists in breaking up that saturation, and each gap has it's "own" slope associated, rather than a bulk overall slope for the entire single gap. As the voice coil integrates opposite sections of the two gaps, a symmetric slope in each gap is essentially negated, and the BL curve is considerably more stable in shape and magnitude. Meaning under power and heavy operation. The corners of the curve - where the voice coil starts to leave one gap, and mainly integrate the internal/external fringe fields and a single gap - are softened and sloped as one would expect, but for the center part of operation the effects of flux compression and B field distortion from power in the voice coil is substantially negated.

All this said, if one designs a full-out overhung or a full-out XBL motor with the goal being high sensitivity and stroke and bandwidth, you'll find that you typically get the same results but in a more compact, lighter (and therefore lower cost - you know you basically "pay by the pound" for motor parts), and linear design with the XBL. Only when you ignore some of the benefits you achieve from the shorter voice coil and the multiple gaps does an XBL design fall in line with most other motors. And when you add in scalability of design (there are 10mm microdrivers, headphone drivers, tweeters, and tiny to huge midranges and woofers with it) these benefits become realizable to all speakers. In many applications, longer overhungs simply are not an option for mechanical mounting purposes, such as in laptops, phones, and plasma TV speakers.

With regards to promises of clarity and bandwidth and sensitivity, I'll say no more than look at the recording monitor of the decade, the Event Opal. This is the monitor of choice by Alan Parsons, John Merchant, James Lovelle, Focus and dozens more of the top engineers and producers in all genres of music. Event Opals use the XBL motor with great results. Much of the reduced flux modulation (and hence, less dynamic compression) and greater bandwidth that comes from highly reduced inductance, and greatly increased linear stroke (and hence more dynamics) is what has led to this monitor's virtual takeover of the top end of the recording studio chain.

Perhaps you'll be at ALMA or CES and we can discuss this further? If so, drop me a line. If you do come to ALMA, look up my new FEA company - DYNE Analytics. We're releasing an FEA tool for motor design for loudspeaker engineers, one we wrote and rolled ourselves and have extensively tested and confirmed against other packages (notably Maxwell) and measured data (Klippel and others, for hundreds of built drivers of all sizes). Yes, I know a few things about FEA as well, at least enough to write and create FEA packages for magnetics modeling - you learn a lot about parasitic inductance, flux stability under power, and the like when creating the actual modeling tools loudspeaker engineers will use to design the next generation of products.

Dan Wiggins

CTO, ADI

 
Well that was quite the read and a bit over my head, but great info none the less. Thanks for making an appearance in my thread.

 
I choose not to optimize any magnet shapes because I wanted to eliminate differences in material cost and B. The XBL^2 motor does not need a deep magnet stack like overhung, but using the exact same magnets we weed out that difference. Sure, in real life, we could choose the same magnet volume and use a much wider but shorter magnet and it would be stronger. But the same could be done for overhung with a deep t-yoke (think of Fi's examples) so I did'nt feel it was necessary to go down that path.

I don't quit buy that XBLL can simply be shorter. I have played this motor depth game many times and at the end of the day, an underhung motor can't be less deep than an overhung motor etc etc. If you want something to move a lot, you have to have clearance for the cone, spiders and then the end of the voice coil. Pick any point on the voice coil, then pick xmax. That point move move xmax both directions no matter what kind of speaker you have. In the case of underhung and XBLL, the magnet might be less deep, but the gapplate makes up for that difference. You can tuck an underhung or XBLL gap into a frame, but then that frame has to be made that much taller in comparison so the spiders don't hit the gap. Its always the same problem.

With the rebate in the gap, i see that as very similar to an undercut t-yoke which can be implemented on an overhung coil and yield great low inductance benefits such as the AE AV12 and AV15 speakers. I agree, since the design is innate to XBLL motors, its a rather serendipitous advantage to the motor without any additional alterations to the return path.

The tighter gap thing is very troublesome and probably has more to do with suspension differences, but I can also say this, if we double up the layers and use a vc that is twice as short, we need a wider gap obviously, but you also claim you can tighten up the slop in the gap. The problem i see is slop should not only account for rocking problems and tolerances that the suspension and assembly can't account for, but also thermal expansion. When you make the coil thicker oyu need more room for that on top everything else. I'm not saying this is bad or good, it's just the same problems with all coils.

In regard to inductance, in my opinion, by the time you double the turns on the XBLL coil, I don't see the advantage in inductance or flux modulation. I have measured some XBLL subwoofer examples that really have about the same inductance as comparable other types. Just take this example.

DIYCable.com : Intro » Home » Exodus Subwoofers »

Great product and this is not a knock in any way. But its inductance is exactly the same as the TC LMS-R which also does not use a shorting ring over the poll. Both have beefy coils and the normalized BL is within 5% of each other. Without getting in the klippel FEA or integrity of the designs, from a glace, the Max-X has higher xmax and more BL, but not by much but its a larger motor too. I don't like to use real world examples because between those drivers, there are too many other differences to really draw accurate conclusions which is way I FEA'ed examples above with controlled variables.

I have little doubt there are great examples of XBLL drivers out there, as there are great examples of underhung, overhung and LMS drivers. There are a lot more variables that go into making a good driver. The point of my analysis was not to show one design was better than the next, but to show that holding some fundamental constrains, we can't really get anything for free. Now lets get back to work, we're wasting valuable time chatting on a forum!

 
I choose not to optimize any magnet shapes because I wanted to eliminate differences in material cost and B. The XBL^2 motor does not need a deep magnet stack like overhung, but using the exact same magnets we weed out that difference. Sure, in real life, we could choose the same magnet volume and use a much wider but shorter magnet and it would be stronger. But the same could be done for overhung with a deep t-yoke (think of Fi's examples) so I did'nt feel it was necessary to go down that path.
Except it doesn't work nearly as well. Look at the reluctance of steel relative to magnetic material - you have considerable losses with a deep-draw back, and then of course - the costs of steel (and weight) are considerably higher than most ceramic magnets meaning an even more expensive build to get where you want to go. You thus need even more magnet to make up for the extra losses incurred.

Forcing the same magnet dimensions is much like deciding to do an automotive test between different cars, but mandating all shall have the same tires and wheel diameters, or all will use the exact same displacement engine, when in fact choice of tires, wheels, and engine displacement is key to overall performance of the speaker.

XBL allows for a much more efficient use of the volume of magnet utilized, which means lower cost, higher performance, or a mix of both. That is perhaps the primary advantage from a physical build - the shorter, wider magnets - and should not be overlooked as it is crucial in so many applications. And no one ever turns down the lower cost thanks to less magnet - and shallower steel/no bumped backplates - required!

I don't quit buy that XBLL can simply be shorter. I have played this motor depth game many times and at the end of the day, an underhung motor can't be less deep than an overhung motor etc etc. If you want something to move a lot, you have to have clearance for the cone, spiders and then the end of the voice coil. Pick any point on the voice coil, then pick xmax. That point move move xmax both directions no matter what kind of speaker you have. In the case of underhung and XBLL, the magnet might be less deep, but the gapplate makes up for that difference. You can tuck an underhung or XBLL gap into a frame, but then that frame has to be made that much taller in comparison so the spiders don't hit the gap. Its always the same problem.
OK, assume everything in FRONT of the motor is the same; we're talking motor height only. Let's assume the same thickness of backplate, so the reluctance from magnet stack to pole is the same. We're looking at top plate height and magnet stack height.

In 36mm of top plate and magnet stack, I can get you 18mm of one way (rearward) voice coil clearance. And that's for a speaker with 14mm one way linear stroke. So a 1:2 ratio of Xmech:height, and a 1:2.5 ratio of Xmax:height.

I'd be interested to see how much mechanical stroke you can get with an overhung, with 14mm of linear Xmax, and top plate plus magnet stack of 36mm.

With the rebate in the gap, i see that as very similar to an undercut t-yoke which can be implemented on an overhung coil and yield great low inductance benefits such as the AE AV12 and AV15 speakers. I agree, since the design is innate to XBLL motors, its a rather serendipitous advantage to the motor without any additional alterations to the return path.
However, those are static analyses you're most likely doing, correct? Dynamic inductance measurements will show a smoother balance of inductance over current and frequency versus position with the shorting ring placed at the average position of the voice coil - which just so happens to be in the middle of the gap (note this not show up in Klippel as Klippel cannot measure inductance versus frequency).

Take a look at the papers from Button, Skaaning, and Vercelli for information about where best to counter and linearize inductance. There's a reason JBL uses laminations of steel and copper, and all of Ejvind's companies have used sleeves. A ring under the gap helps, but is nowhere near as effective as IN the gap, especially when linearity versus position in taken into account. In a static/small signal analysis it looks great but as you move away from that ring it all goes away.

Additionally, undercutting the pole significantly chokes off flux in the motor, meaning you need a larger diameter voice coil/pole to maintain the same flux level (or much larger magnets). Of course, that increases the native inductance of the voice coil. The rebate in an XBL motor - at most - cuts of half the amount of flux an undercut would, because it's only the upper gap that is affected, thus meaning it's not nearly as limiting as a full undercut.

The tighter gap thing is very troublesome and probably has more to do with suspension differences, but I can also say this, if we double up the layers and use a vc that is twice as short, we need a wider gap obviously, but you also claim you can tighten up the slop in the gap. The problem i see is slop should not only account for rocking problems and tolerances that the suspension and assembly can't account for, but also thermal expansion. When you make the coil thicker oyu need more room for that on top everything else. I'm not saying this is bad or good, it's just the same problems with all coils.
How many layers are required for LMS, relative to XBL? For an average 4 layer LMS, the outer areas are 8 layers, and the inner are 2. Thus you end up with an even larger gap. And we'll not talk about the higher Mms that comes along. Often that Mms is desired - and needed! But many times it is not, and that becomes a limiting factor of application of that approach.

In general, my experience building a few thousand versions of underhungs, overhungs, and XBL (as well as split-coil, as it was covered in the original '72 patent from Babb) is that the gap can be considerably tighter overall with an XBL motor. Adding two more layers (going from a 2 layer overhung to a 4 layer XBL) does not double the width of the voice coil because of stacking of the wires; you see about a 60% increase in width for doubling the layers. Thus one reaches a doubling of L without a corresponding increase in gap width and the corresponding loss of flux.

In regard to inductance, in my opinion, by the time you double the turns on the XBLL coil, I don't see the advantage in inductance or flux modulation. I have measured some XBLL subwoofer examples that really have about the same inductance as comparable other types. Just take this example.
DIYCable.com : Intro » Home » Exodus Subwoofers »

Great product and this is not a knock in any way. But its inductance is exactly the same as the TC LMS-R which also does not use a shorting ring over the poll.
Take a look at inductance over current and frequency versus position (of course, over frequency versus position is difficult to do, since Klippel cannot measure it, you need to either analyze it or measure with different tools). Dynamic stability is increased with the bulk of the inductance countering being right in the middle of the gap.

If analyzing, remember to set the current negative to position, too; most people don't realize that when the driver is moving forward, the current is actually NEGATIVE; current is negative the position of the coil, and that is why so many get inductance compensation wrong - they place too much copper or aluminum at the wrong position (and, more often seen, too much at that wrong position as well).

I have little doubt there are great examples of XBLL drivers out there, as there are great examples of underhung, overhung and LMS drivers. There are a lot more variables that go into making a good driver. The point of my analysis was not to show one design was better than the next, but to show that holding some fundamental constrains, we can't really get anything for free. Now lets get back to work, we're wasting valuable time chatting on a forum!
I guess my point is that you are holding "fundamental constraints" arbitrarily that negate the advantages of XBL.

XBL will yield shorter motors for a given level of mechanical and linear stroke (meaning lower costs, or wider - and thus higher flux - motors). That's a straight geometric proof; it's hard to argue.

XBL will give you greater inductance stability over stroke because of the placement of the shorting rings in the middle of the gap (and does not incur the flux loss issue when you sleeve the pole). Pure research papers from others in the field, as well as measurements and FEA simulations will confirm this result.

XBL provides for greater B field stability over power because of the breaking up of the gap into multiple parts, so skewed fields are not as much of an issue (which is usually addressed by assuring another point in the magnetic path - usually the backplate-to-pole junction - is saturated at all times, meaning a loss in total flux in the motor). Again, measurements, theory, and FEA all coincide to show this to be the case.

I'm not anti-overhung; I use it quite a bit for many things. Likewise underhung as well. However, there are several distinct advantages of XBL motors that I feel your analysis simply ignored; I'm just providing a little more insight into the situation and hopefully providing some input into why holding parameters arbitrarily constant is not a good engineering exercise as it does not provide a real-world look at the issues at hand.

 
Fair enough, i think we made all of our points as well as we could.

I'll respond your overhung depth challenge:

I'm assuming you're using dual 4mm gaps in a 20mm tall xbll gap plate with 16mm tall magnet with a 16mm tall voice coil.

How about a 32mm voice coil with a 32mm tall magnet with a single 4 mm gap. That gives me 14mm xmax and 18mm xmech at the same depth.

One last thing about inductance over displacement - while i have not done AC analysis myself, i feel its less important because if the voice coil is moving quit a bit, the inductor portion of the motor is basically a short circuit no matter what the value is at that point because which is obviously why inductance is a low pass filter - it just doesn't matter too much down low because its a short circuit. By the time the inductance really kicks in, the displacements are very small. How much that matters without any math to back it up is debatable and i'm not gonna divulge in that conversion, but I do feel this last point needs to be made in light of all loudspeakers.

 
So, i happen to know the Owner of CSS, and its some good news, the SDX15 is being re-designed so that it will have more than 34mm one way excursion! I currently own the SDX15 in my home as a theater subwoofer. 16 cubes tuned to 15hz, its one of the best subwoofers i've ever heard, and i've worked with Velodyne servo controlled 18's. factor in that the raw SDX 15 driver was about $300 and that the velodynes with servo's are usually $3k+ i'll keep my sdx, and am looking forward to the new versions.

The trio 8 is pretty much unmatched $ to performance right now.

and find another 12" like the trio 12 that for the dollar has the same performance.

The owners name is Bob, and he definitely has a handful of products most companies can't touch right now.

He's in the perfect pricing/performance ratio's to be one of the best, and the products are TOUGH!

My buddy and i built a 92" tall folded horn enclosure for the Trio12, about 100db sensitivity right down to 20hz. The box was huge, but the driver held up to a fairly high compression horn, and never complained.

 
So, i happen to know the Owner of CSS, and its some good news, the SDX15 is being re-designed so that it will have more than 34mm one way excursion! I currently own the SDX15 in my home as a theater subwoofer. 16 cubes tuned to 15hz, its one of the best subwoofers i've ever heard, and i've worked with Velodyne servo controlled 18's. factor in that the raw SDX 15 driver was about $300 and that the velodynes with servo's are usually $3k+ i'll keep my sdx, and am looking forward to the new versions.
The trio 8 is pretty much unmatched $ to performance right now.

and find another 12" like the trio 12 that for the dollar has the same performance.

The owners name is Bob, and he definitely has a handful of products most companies can't touch right now.

He's in the perfect pricing/performance ratio's to be one of the best, and the products are TOUGH!

My buddy and i built a 92" tall folded horn enclosure for the Trio12, about 100db sensitivity right down to 20hz. The box was huge, but the driver held up to a fairly high compression horn, and never complained.
Any idea on a recommended box size for the SD12? Im contemplating running a single 12 in my car.

 
Activity
No one is currently typing a reply...
Old Thread: Please note, there have been no replies in this thread for over 3 years!
Content in this thread may no longer be relevant.
Perhaps it would be better to start a new thread instead.

Similar threads

I had two Skar amps (4ch & a monoblock) go bad within a year. Post #2 is an excellent recommendation.
6
1K
Following since any info on the neo version is non-existent
3
1K
The Regulator for my car is built into the harness, I keep forgetting that VAG cars are fucktarded sometimes.
5
1K
Check out Sonic Electronix as well. They have some great deals usually and excellent Customer Service also. I like to buy my HUs /Head Units from...
6
355

About this thread

whitedragon551

5,000+ posts
Moderator
Thread starter
whitedragon551
Joined
Location
IL
Start date
Participants
Who Replied
Replies
28
Views
4,270
Last reply date
Last reply from
ciaonzo
Screenshot_20240518-030709~2.png

1aespinoza

    May 18, 2024
  • 0
  • 0
1000007975.jpg

Mr FaceCaser

    May 16, 2024
  • 0
  • 0

New threads

Top