seems like everytime this conversation comes up, it becomes a war of tradeoffs.... first of all, as Nick said, its simply wound that way to create the linear BL effect. Thats what the "LMS" is.
But in fact, lms coils (production version) are actually wound to a max of 4 layers which is the exactly same wind as a standard voice coil, be it TC-1000, 2000, 3000, 5200 etc etc... 8 layer flat is about the same as 4 layer round, so just ignore that bit for now. The LMS becomes less efficient not because of a wider gap, but because coil cross section is removed from the middle to in fact lower the BL and flatten the curve. Moving mass is actually lower in LMS drivers than a non-lms TC counterpart, however this is irrelevant. Moving mass alone does not define sensitivity, ignoring cone differences, its really a function of the force to weight ratio. Same principals that governs pretty much everything else. So the reason LMS drivers are less efficient is because they have lower L, not a lower B from a wider gap. The gap is the same, and the B in the gap is the same too! Its a moot Lpoint really because its the same effect (except for a bit of inductance advantage on the LMS behalf) Less L or less B gives you less BL, but I just want to make that point anyway //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
the newer LMS-5400 and LMS-Ultra actually use a very efficient motor even with the lms voice coil. BL^2/Re of around ~180 which is just shy of a Fi BTL to give you an idea of the motor strength.. not bad to a motor that throws away almost half of its BL to linearize the curve. It actually works out exceptionally well in the 4HP platform because the original 4HP was over motored to the point of near un-useability(45Tm to be exact). Qts of 0.15 made it very hard to work with without massive EQ and voltage on hand... so the 5400 was perfect. Also inductance has proven to be a non-issue on the LMS woofers as the frequency response (true test of inductance filter issues) was flat up to 200Hz...) "Nothing above 50Hz" is quite incorrect. That may have been true for the first generation LMT which was very in efficient and inpratical up high because of the sensitivity (not inductance btw
Like LMS :: overhung designs, xbl motors are also less efficient than standard underhung designs too, and they carry their tradeoffs ... Good argument, you can alway fill in that part in the notch in the gap with steel and gain quite a bit of sensitivity in an XBL^2 motor by converting it to a std underhung... the xmax will go down, but thats the point right? I can do the same thing to an LMS just put a normal coil in the motor and get a normal overhung... sensitivity goes up in both cases and linear xmax drops, and distortion increase and dynamic prediction and modeling become less accurate... etc etc...
so technically Nick, you kind of got it backwards....
XBL^2 has the wide gap and throws away B
LMS has the normal gap and throws away L
But the appropriate way to say it would be xbl notches the gap, lms notches the coil. take your pick...
I will also arge that neither is better!
As a shallow mount design. the working displacement is the difference of your gap and coil. longer coil... deeper motor....or taller gap. Its the same distance any way you slice it. You can tuck and overhung coil inside the gap just as an underhung too. In fact Chad just posted a picture of one above.
xbl^2/lms.....not one is better/worse, they actually have quite a bit of differences on top of that too because they are underhung vs overhung, but I think they both work to do the same thing.... lower distortion, and they both succeed.
NDMstang65... lms woofers have low-ish inductance for their size, and I'm very shocked you don't like the sound of a lms woofer. because it really has no sound at all other than what you hear.. perhaps its the music thats the issue? lol
As would any linear woofer true to its word, its a lack of distortion. You can get good Qts and good sensitivity from an LMS woofer, or XBL^2 it may take a larger magnet, but i can tell you from personal expeirnce, nothing compares when done right. Sure it may be larger and more expensive, or otherwise it may have a poor QTS and poor sensitivity making it impractical for anything above 40Hz (for example)
But don't take my word for. Take this guys... he has listened to quite a few subs and has the measurements to prove it. His woofer of choice (the 5400 by a "landslide")
I will say this right now, I'm not trying to show its the greatest thing since slided bread, its got its own drawbacks... many of them, but don't just count out LMT because of what some competitor to TCS said 6 years ago when TC released its first LMT woofer... wake up and read results.
http://www.hometheatershack.com/forums/subwoofer-tests/8144-subwoofer-tests-round-5-6th-october-2007-test-summary-read-me.html
http://www.hometheatershack.com/forums/home-audio-subwoofers/6656-subwoofer-tests-fall-2007-a.html
final note:
You can take all the subject tests you want and subjectivity convince people that they should be subjectively listening to subjective music the same subjective way you would... I couldnt care less.. the results speak for themselves... and they "objective"
