LMS-5400 buy-in - Page 17 - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #161 of 312 Old 09-21-07, 09:07 PM
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Re: LMS-5400 / RL-p18" buy-in

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o quite different than the Tumult or the TC-2000s I measured last time. Then there is also power compression. The massive 4" VC with titanium former should perform really well when some real men power will be utilized. Then we will know more about the real difference to "weaker" drivers.
for a GP session this fall.
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post #162 of 312 Old 09-21-07, 10:35 PM
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Re: LMS-5400 / RL-p18" buy-in

Ilkka, the free air measurements of the two TC2k drivers appear to be better behaved at the top end as compared to the measurements while in an enclosure. Why is that?

According to Dan Wiggins (who has kind of been taken down a notch in my mind after your testing), inductance was supposed to be a big problme for LMS motor technology, but clearly that doesn't seem to be the case. So it begs the question of whether or not this motor technology could be put to use to make an ultimate midrange/midwoofer. I'm still puzzled why the Tumult had such poor inductance when the coil should theoretically be pretty short. Also, Dan appears to be off the target on his commentary on dual spiders as well.


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post #163 of 312 Old 09-21-07, 10:52 PM
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Re: LMS-5400 / RL-p18" buy-in

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funky_waves wrote: View Post
YAH RIGHT, lok what i did to mine, and they where the oem10 passives with extra strong cones. dual passive enclosure with a single OEM10 both passives went. took very little figer presure to turn the cone out like that afterwords

I guess those ti cones would help then
 
post #164 of 312 Old 09-22-07, 12:42 AM
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Re: LMS-5400 / RL-p18" buy-in

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Ilkka, the free air measurements of the two TC2k drivers appear to be better behaved at the top end as compared to the measurements while in an enclosure. Why is that?
Does it really? If you look at the THD graphs below, you can see that the upper one does have a dip at around 18-21 Hz (orange curve). That's the Fs of the driver (18 Hz by the spec). THD dips there because current varying inductance Le(i) (also known as flux modulation) dips there too. Impedance peak is at Fs, so the current through the VC will be low.

When put in an enclosure, Fb raises up. Now the impedance peak is at around 40 Hz. That's the Le(i) and THD minimum point now. Sealed enclosure also prevents back wave cancellation, unlike free-air "alignment". Combine these two and you'll realize that it only seems like the driver would behave better at the upper-end while measured in free-air. Also notice that the absolute sound pressure levels between these two measurements can not be compared.





Quote:
According to Dan Wiggins (who has kind of been taken down a notch in my mind after your testing), inductance was supposed to be a big problme for LMS motor technology, but clearly that doesn't seem to be the case. So it begs the question of whether or not this motor technology could be put to use to make an ultimate midrange/midwoofer. I'm still puzzled why the Tumult had such poor inductance when the coil should theoretically be pretty short.
It seems that inductance and its effects on performance are probably one of the hardest things to simulate properly. The most commonly used, Le at 1 kHz, value is totally useless with subwoofer drivers. The more accurate Ls, Lp, Rp triplet seems to work pretty well with more traditional motor topologies, but not with LMS (or else the figures given by the TC Sounds are wrong).

It is also important to notice that the inductance varies with both excursion (Le(x)) and current/frequency (Le(i)). Here's an inductance simulation done on the AA Tumult 15D2 MK2. It was on AA's website while it was still up. Notice how the inductance raises really high during the backstroke, especially at low frequencies. That is normal behaviour since during the backstroke there is more iron inside the coil.



Below is a Klippel analyzer measurement on an Eclipse LMT SW8200 (by npdang at Diy Mobile Audio). It shows that the inductance variation with the excursion is really small. Maybe this is one of the reasons why the LMS seems to have such a good upper-end performance?

edit: These two inductance measurements are NOT comparable.



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Also, Dan appears to be off the target on his commentary on dual spiders as well.
Could you refresh my memory?
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post #165 of 312 Old 09-22-07, 01:04 AM
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Re: LMS-5400 / RL-p18" buy-in

Ilkka, I should have been more specific. I wasn't referring to the higher frequency distortion, but the actual FR. In the free air measurements, the dropoff at 100hz is less than it is when the driver is in an enclosure.


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post #166 of 312 Old 09-22-07, 01:13 AM
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Re: LMS-5400 / RL-p18" buy-in

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Ilkka wrote: View Post

Could you refresh my memory?
I saw this the other day: http://forums.audioholics.com/forums...ad.php?t=21421

You posted in that thread.

Anyways, about half the way down, a post by ssabripo (from Wiggins) talks about dual spiders.
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post #167 of 312 Old 09-22-07, 01:13 AM
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Re: LMS-5400 / RL-p18" buy-in

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Ilkka, I should have been more specific. I wasn't referring to the higher frequency distortion, but the actual FR. In the free air measurements, the dropoff at 100hz is less than it is when the driver is in an enclosure.
Yes, that's the Qtc in effect. In free-air/IB the Qtc will be close to Qts, meaning very low (~0.3), but in an 70 liter enclosure (my own dual subwoofer), the Qtc will be around 0.7. That is what makes the frequency response to change its shape.
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post #168 of 312 Old 09-22-07, 01:30 AM
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Re: LMS-5400 / RL-p18" buy-in

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WillyD wrote: View Post
I saw this the other day: http://forums.audioholics.com/forums...ad.php?t=21421

You posted in that thread.

Anyways, about half the way down, a post by ssabripo (from Wiggins) talks about dual spiders.
Oh yeah, I remember that.

Well, even though I greatly respect Mr. Wiggins (and Hyre too), I have to say that the XBL^2 has been a slight letdown. So therefore I would take his "other" info with some reserve.
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post #169 of 312 Old 09-22-07, 08:08 AM
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Re: LMS-5400 / RL-p18" buy-in

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Ilkka wrote: View Post
Oh yeah, I remember that.

Well, even though I greatly respect Mr. Wiggins (and Hyre too), I have to say that the XBL^2 has been a slight letdown. So therefore I would take his "other" info with some reserve.
i wouldn't necessarily call it a "letdown" per se, but I hear ya.... In its defense though, I have to say the XBL^2 drivers I've played with (Avalanche, tumult) have had some of the cleanest, most accurate bass I've heard, including the older LMT15 (pre-cursor to the LMS 5400).

But yeah, some of the hoopla on the XBL^2 in that paper by Dan has been proven to not be exactly the case.

ps- just to clarify, not all those comments are straight from Dan. Some of it came comments from Deon Bearden and Tom Nousaine


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Last edited by ssabripo; 09-22-07 at 08:13 AM.
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post #170 of 312 Old 09-22-07, 01:11 PM
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Re: LMS-5400 / RL-p18" buy-in

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ssabripo wrote: View Post
i wouldn't necessarily call it a "letdown" per se, but I hear ya....
I started to feel a little bit bad about that sentence so I edited it.

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In its defense though, I have to say the XBL^2 drivers I've played with (Avalanche, tumult) have had some of the cleanest, most accurate bass I've heard, including the older LMT15 (pre-cursor to the LMS 5400).
Exactly. And that leads us to the real million dollar question: Is slightly higher upper-end (say above 40-50 Hz) distortion actually preferred by many? Does it make the driver sound more accurate and punchy because there is more high frequency content in the mix?
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