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<blockquote data-quote="Kyle_Keating" data-source="post: 7132786" data-attributes="member: 582385"><p>That write up is heavily misguided and old information (2005?), I have fea'ed both designs under a variety of variables and constants. The initial lure of XBL^2 was promises of ultra high sensitivity, flat BL and low inductance - in truth the only way to get that is the same way as always. You can't just get something for free.</p><p></p><p>The facts are this. They both are limited by the exact same math so there is little SPL or inductance advantage between the two designs.</p><p></p><p>They both can have either low or high inductance. If you don't double up the turns on the XBLL coil compared to the longer overhung or lms coil, you're sensitivity will be considerable lower. When you double the turns, you bring the inductance right back up. Same game, different name. Shorting rings can be applied inside the gaps, but this is no different than n undercut lms or overhung gap with a shorting ring in it.</p><p></p><p>Secondly they both have about the same sensitivity (LMS is not more power hungry) when you hold the xmax, magnet size, resistance and moving mass to a constant. XBLL is not more efficient than more motor designs, the very nature of the design makes it less efficient than an overhung coil that can move of equal xmax. Its not mathematically possible for it to be more efficient or even as efficient and here is why…</p><p></p><p><img src="http://www.data-bass.com/fea/over_hung_flux.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>standard overhung motor (also works for lms coils)</p><p></p><p><img src="http://www.data-bass.com/fea/xbll_motor_flux.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>equivalent XBLL motor with the same xmax limit. This design has a 50% shorter coil than the overhung design, but two gaps. There are two FEA models of this motor. 1 with the same gap width and number of layers as the overhung voice coil (4) and an (8) layer version with a wider gap but it has the same moving mass and resistance as the overhung example.</p><p></p><p><img src="http://www.data-bass.com/fea/B_all.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>A quick glance shows the flux from the XBLL motor is divided between two gaps compared to the higher density single gap of the overhung/lms motor.</p><p></p><p><img src="http://www.data-bass.com/fea/BLplot.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p><strong>This coil is 9.3 ohms at a fixed length L and fixed gauge G</strong></p><p></p><p>Here you can see the BL curve at a fixed power load for the overhung motor. Not very linear, but it is efficient.</p><p></p><p><img src="http://www.data-bass.com/fea/BLI_xbl.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p><strong>This coil is 4.65 ohms at a fixed length L/2 and fixed gauge G</strong></p><p></p><p>Here we can see the XBLL curve with the same power load. We can see it does have have nearly the same force, but it also has a less L because its coil is much shorter (50% exactly) The voltage was decreased for this model to match the power level of the overhung coil because the XBLL coil has 50% less resistance. If you don't match the power level you don't see the real sensitive difference. In this case we can observer XBLL is NOT very efficient, so we must increase the number of turns to bring up the L back to a normal level and gain back our sensitivity.</p><p></p><p><img src="http://www.data-bass.com/fea/BLI_xbl8.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p><strong>This coil is 9.3 ohms at a fixed length L/2 and fixed gauge G</strong></p><p></p><p>The 8 layer example is much better, but surprisingly with the same L, same moving mass and same resistance, we STILL don't reach the maximum sensitivity of the non-linear overhung coil. We get pretty close, but we also forgo the lower inductance of the smaller coil because we beef'ed it back up again. But we do still maintain linear control which is good, but its NOT free.</p><p></p><p>Now lets look at 1 LMS example similar to the 4 layer XLLL example. The</p><p></p><p><img src="http://www.data-bass.com/fea/lms_coil.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p>This is one example of how to make an LMS coil from a 4 layer overhung coil - we cut out winding to linearize the L to counter the non-linear B (sort of like an inverse)</p><p></p><p><img src="http://www.data-bass.com/fea/BLI_lms.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p><strong>This coil is 7.4 ohms at a fixed length L/2 and fixed gauge G</strong></p><p></p><p>You can see we have very fine control over the BL curve and it does produce very flat results, but holding the power constant we do lose sensitivity just as the XBLL coil. Also, like the 4 layer XBLL coil, we also reduce the resistance and therefore don't have the same moving mass or L comparable to the overhung coil. a 4 layer LMS coil is not entirly comparable to the 4 layer overhung coil (just as we saw with the XBLL examples) So we really need to beef up the LMS coil to the same moving mass. Mathematically this works out to a 5 or 6 layer LMS coil give or take and the results come out similar to the 8 layer XBLL coil with the exact same moving mass fixed to the same power load.</p><p></p><p><img src="http://www.data-bass.com/fea/lms_xbll.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></p><p></p><p><strong>Here is our fixed resistive and fixed mass examples</strong></p><p></p><p>We have to widen the gap by the width of 1 layer for the quasi-5 layer LMS example, this model does not quit show that, but its very close. In realitiy, the LMS coil would have just a tad lower force.</p><p></p><p>At the end of the day they are both about the same sensitivity (the XBLL may have a slight advantage but its much less than what is proposed by this author). Neither has an inductance advantage. There are examples of very low inductance LMS drivers as well as XBLL drivers. There are also examples of very high inductance XBLL drivers and LMS drivers (don’t pick specific examples for general comparisons because the variables involved are different in every application)</p><p></p><p>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.</p></blockquote><p></p>
[QUOTE="Kyle_Keating, post: 7132786, member: 582385"] That write up is heavily misguided and old information (2005?), I have fea'ed both designs under a variety of variables and constants. The initial lure of XBL^2 was promises of ultra high sensitivity, flat BL and low inductance - in truth the only way to get that is the same way as always. You can't just get something for free. The facts are this. They both are limited by the exact same math so there is little SPL or inductance advantage between the two designs. They both can have either low or high inductance. If you don't double up the turns on the XBLL coil compared to the longer overhung or lms coil, you're sensitivity will be considerable lower. When you double the turns, you bring the inductance right back up. Same game, different name. Shorting rings can be applied inside the gaps, but this is no different than n undercut lms or overhung gap with a shorting ring in it. Secondly they both have about the same sensitivity (LMS is not more power hungry) when you hold the xmax, magnet size, resistance and moving mass to a constant. XBLL is not more efficient than more motor designs, the very nature of the design makes it less efficient than an overhung coil that can move of equal xmax. Its not mathematically possible for it to be more efficient or even as efficient and here is why… [IMG]http://www.data-bass.com/fea/over_hung_flux.jpg[/IMG] standard overhung motor (also works for lms coils) [IMG]http://www.data-bass.com/fea/xbll_motor_flux.jpg[/IMG] equivalent XBLL motor with the same xmax limit. This design has a 50% shorter coil than the overhung design, but two gaps. There are two FEA models of this motor. 1 with the same gap width and number of layers as the overhung voice coil (4) and an (8) layer version with a wider gap but it has the same moving mass and resistance as the overhung example. [IMG]http://www.data-bass.com/fea/B_all.jpg[/IMG] A quick glance shows the flux from the XBLL motor is divided between two gaps compared to the higher density single gap of the overhung/lms motor. [IMG]http://www.data-bass.com/fea/BLplot.jpg[/IMG] [B]This coil is 9.3 ohms at a fixed length L and fixed gauge G[/B] Here you can see the BL curve at a fixed power load for the overhung motor. Not very linear, but it is efficient. [IMG]http://www.data-bass.com/fea/BLI_xbl.jpg[/IMG] [B]This coil is 4.65 ohms at a fixed length L/2 and fixed gauge G[/B] Here we can see the XBLL curve with the same power load. We can see it does have have nearly the same force, but it also has a less L because its coil is much shorter (50% exactly) The voltage was decreased for this model to match the power level of the overhung coil because the XBLL coil has 50% less resistance. If you don't match the power level you don't see the real sensitive difference. In this case we can observer XBLL is NOT very efficient, so we must increase the number of turns to bring up the L back to a normal level and gain back our sensitivity. [IMG]http://www.data-bass.com/fea/BLI_xbl8.jpg[/IMG] [B]This coil is 9.3 ohms at a fixed length L/2 and fixed gauge G[/B] The 8 layer example is much better, but surprisingly with the same L, same moving mass and same resistance, we STILL don't reach the maximum sensitivity of the non-linear overhung coil. We get pretty close, but we also forgo the lower inductance of the smaller coil because we beef'ed it back up again. But we do still maintain linear control which is good, but its NOT free. Now lets look at 1 LMS example similar to the 4 layer XLLL example. The [IMG]http://www.data-bass.com/fea/lms_coil.jpg[/IMG] This is one example of how to make an LMS coil from a 4 layer overhung coil - we cut out winding to linearize the L to counter the non-linear B (sort of like an inverse) [IMG]http://www.data-bass.com/fea/BLI_lms.jpg[/IMG] [B]This coil is 7.4 ohms at a fixed length L/2 and fixed gauge G[/B] You can see we have very fine control over the BL curve and it does produce very flat results, but holding the power constant we do lose sensitivity just as the XBLL coil. Also, like the 4 layer XBLL coil, we also reduce the resistance and therefore don't have the same moving mass or L comparable to the overhung coil. a 4 layer LMS coil is not entirly comparable to the 4 layer overhung coil (just as we saw with the XBLL examples) So we really need to beef up the LMS coil to the same moving mass. Mathematically this works out to a 5 or 6 layer LMS coil give or take and the results come out similar to the 8 layer XBLL coil with the exact same moving mass fixed to the same power load. [IMG]http://www.data-bass.com/fea/lms_xbll.jpg[/IMG] [B]Here is our fixed resistive and fixed mass examples[/B] We have to widen the gap by the width of 1 layer for the quasi-5 layer LMS example, this model does not quit show that, but its very close. In realitiy, the LMS coil would have just a tad lower force. At the end of the day they are both about the same sensitivity (the XBLL may have a slight advantage but its much less than what is proposed by this author). Neither has an inductance advantage. There are examples of very low inductance LMS drivers as well as XBLL drivers. There are also examples of very high inductance XBLL drivers and LMS drivers (don’t pick specific examples for general comparisons because the variables involved are different in every application) 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. [/QUOTE]
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