The NEXT Best Thing : to a TC Sounds LMS 18" Driver

Well the closes thing that matches and exceeds in some ways, the build quality of the LMS is the acoupower 18, however, Kevin's Maelstrom X is the newest high power alternative to the LMS, it models very similar, its more a of a cross between an LMS and an RL-p18. It takes smaller boxes than the Rl-p18, larger boxes than the LMS, the RL-p18 likes about 6.5cubic feet in a sealed box, the Maelstrom likes about 4.5 cubic feet, the LMS likes about 3.5 cubic feet (maybe a little less even). The RL-p18 has 27.6mm xmax, the Maelstrom has 33mm, the LMS has 38mm. The RL-p uses a traditional motor, the Maelstrom uses XBL, the LMS uses the TC Sounds Linear motor technology (LMT). The one biggest difference between the Maelstrom and the LMS is power handling, the Maelstrom can prolly take about 1000watts continuous, whereas the LMS can take about 2,500watts, both seem inferior to the acoupower in this regard.

Lest we forget the difference in the suspension systems. Two 10" spiders on the LMS5400, dual 8.5" on the Rl-p, and ____ on the Maelstrom-x?

The maelstrom looks like it will have a single spider suspension, probably to account for its low fs, if it does its spec'd excursions, then I don't care what it rides on, many of my favorite subs are single spider suspensions, and not even because they are cheaper. The effects of the suspension are rather ambiguous in terms of how it will actually affect the sound of the sub. The suspension was one of the traits I was referring to when I said that the build quality on the LMS was better.

Judging power handling is very difficult, the acoupower drivers can't take the small boxes like these others can, the smallest I'd go would be about 7 cubic feet, and that would be pushing it more than I am on the others. I see no reason why the maelstrom won't perform very well in a smaller sealed, its only drawback is its power handling, depending on how much you really thrash your sub, this may or may not be an issue. I'd wouldn't have the least bit of a problem putting 4-8000watts behind an acoupower, prolly 2000-5000 on the LMS, 1000-2000 with the maelstrom. The one driver that would be very nice would be Kevin's still in design, "sicko" 18, 54mm xmax, 70-75mm xmech, similar power handling to the LMS and pretty much the same parameters as the Maelstrom. IMO 4.5 cubes isn't all that big for a sealed 18 box, thats a 22" cube if you make it from 3/4" BB ply with a bit of bracing. The real nice thing is when you start throwing PR's on these guys you can tune them down to the mid teens and see a massive boost in output.

I never said the suspension played a huge part in how the sub sounds. But to dismiss it completely as if it doesn't play a part in the subs overall performance is foolish. Low end distortion will be significantly higher on a sub with a lesser suspension.

I don't have much time to converse but I'll make a couple quick points.

#1. Power handling is dominated by the VC/former size and surface area and how much air is passing over them in a given time. Assuming your comparing VCs & formers of roughly the same size and construction you get power handling that is very comparable.

#2. In home audio, the dominant form of compression is BL compression, not power compression. In pro-audio, that changes due to prolonged high power operation. The only home audio situation where you may become power handling limited (with the Maelstrom-X) is where you are using massive equalization in a small box. In normal unassisted alignments, the failure mode will most likely be mechanical, rather than thermal with the Maelstrom-X. It has the same functional power handling as the old Tumult and we didn't see a lot of thermal failures with those, which where a smaller box driver that was used frequently in heavily equalized systems.

Willy, I wasn't disagreeing with you, just expounding on the little I know about the different suspensions

In fact, it looks to me like we are on the same page

Kevin, I can't tell you excited I am by this, the Tumult could handle LOADS of power, a buddy of mine brought over a ported one a long time ago and he was driving it with a RMX 4050HD, we even drove the amp to clipping a few times just for fun, the driver still sounded good.

A quick note on suspensions too since that seems to be a hot topic.

The suspension has a pretty easy function. It keeps the VC/former centered, in the gap and it provides a parabolic spring-like function to keep the cone centered ala positive/negative stroke. The force, as you progress from center position, either front or rearward should progressively get stiffer, up to the limits of the driver.

What you try to achieve with a good Cms/Kms curve is symmetry. You try to get the force suspension stiffness to be symmetric front to rear. Pretty much all drivers have some asymmetry which produces some 2nd harmonic. Why... well the surround isn't always symmetric in construction, the spider is often attached differently and the air-load on the parts differs front/rear. All of those factors increase non-linearity.

The other obvious design factor is stiffness. You aim for a certain stiffness to achieve a given set of T/S parameters. Of course the stiffness isn't static, it changes with movement front/rear but that is just a fact of life.

If you achieve these things, then it matters not if you use one or two spiders. Using two spiders is often a method used to minimize rocking. If you don't have rocking with one spider, there isn't much sense in using two. If it bought me anything I'd do it in a minute because a second spider adds very little cost to a design.

In all our drivers we control rocking via other methods, essentially in the design of the coil/former in relation to the suspension. In all our designs, the suspension does not limit total travel. Our suspensions are capable of fully supporting the full MECHANCAL limits of throw. What finally limits the driver in all our designs, is the former hitting the back plate. How often does this happen? Not much... .so far this year I've had one returned where the user actually overpowered the driver and there wasn't any ambiguity about why.

yo Kev....you still haven't answered my PM!

Stop consuming his time Sherv; he's busy building my Maelstroms

Larry

Kevin,

"In home audio, the dominant form of compression is BL compression, not power compression."

That's a new one on me, unless it's the same thing as BL modulation, but IMO that's different than compression...

Sorry.... those things are not the best way to get in touch with me. Email me and I respond but I frequently miss those PMs.

They are on my site. I don't have a ton of pictures yet but all the specifications are pretty much finalized. I'll break-in four units from the production run and get final parameters but they won't shift much.

http://www.diycable.com/main/product...roducts_id=681

Ha... some Chinese girl is building them not me.

LOL

thanks!

Well.... if you take away motor strength with stroke what happens? You get a compressed signal. With a typical parabolic BL curve it doesn't take long to get 10% BL reduction as the cone leaves center. True, this mainly effects the peaks rather than the depressing the entire signal but you if you integrate the area of compression, and compare it with the integral of the signal loss due to power compression, the math will show that you have higher loss due to the loss of BL as the coil leaves the center of the gap in comparison to power compression at low to moderate power levels.

This is a generalization and the balance of where one dominates over the other is going to change in every circumstance. For midwoofers and subs at normal operating levels (not max output), it is a good generalization.

"Well.... if you take away motor strength with stroke what happens?"

Gotcha, compression due to BL sloping off.

Interesting concept; so how many dB compression is there at 70% BL for a conventional motor?

Depends on the driver. If you want to simulate it, create two drivers, one with 30% less BL. You have to do the math to make sure none of the other parameters change EXCEPT due to the loss of BL. Then model both and overlay the response. With LSPCad you can allow it to update other parameters in response to a change in just one. It basically calculates the effect on other parameters if you change one of the fundamental parameters like mass, BL or Cms.

Its just a slice of the pie view because most of us don't run drivers under normal use at X-max.

Looks like this guy will have the a similar motor and suspension to the old tumults, given that its now an 18" driver with more BL and the same excursion that costs quite a bit less, I can't be happier with Kevin for his new sub, a more extensive suspension could up the driver costs significantly.

"create two drivers, one with 30% less BL. "

The 30% is only at the endpoints of the excursion range being considered.

But even if it were 30% less in that whole range, and SPL is proportional to BL (not sure if that's right), it would be only 1.5 dB compression.

That Maelstrom-X 18" looks like a great deal. XBL^2, shorting rings, 33mm xmax with 42mm xmech, and it likes a big enclosure. Perhaps the new LLT default, as it comes in cheaper than the RL-p18 and with what would appear to be a better motor and better upper bass FR linearity than both it and the Q18. Nicely done Kevin.

It also likes small boxes, which is what makes the PR option so attractive, 7 cubes tuned to 15Hz or so looks very nice, you could even do a small ported version if you wanted, 7 cubes tuned to 19Hz with one of those 7" acoupower ports, you wouldn't be able to drive the sub to xmax, but it would give you 120dB+ to 20Hz and a hair below.

Hopefully.

What I like about it is that it doesn't require or love really big enclosures. It can roll in medium sized enclosures quite well it appears.

Furthermore, we finally have a high performance 18 that can swing small sealed if we want, 4.5 cubes gets a 0.7 Q, but you can smaller if you want, I'd do 4 cubes with some stuffing, perhaps even less, the issue starts to become the amount of power you want to dump into the vc, although, according to bosso, that isn't an issue with tumults, and this guy has the same power handling, if thats the case, I wouldn't have a problem doing 3 cubes with an LT.

It isn't necessarily proportional. I don't have my laptop with me (that has LSPCad) or I'd simulate something quick.

Here is the Kepler, my 2-way monitor speaker that uses a midwoofer with XBL^2 and about 10mm of x-max.

This is a deviation from linearity measurement done in the chamber at the National Research Council of Canada (NRC). The first graph is at 96dB 1M, the second at 101dB @ 1M. Compared to subs, this is a tiny voice coil @ 1.5" in diameter and the former is about the same in length.

I don't know why I'm showing this other than to say that the compression in real-life at normal listening levels, is not that severe. The 96dB @ 1M is louder than you would see in a home environment under normal use. It is a good metric for transients and you can see it shows less than a dB of compression in the midwoofer. The 101dB @ 1M is extremely loud, much louder than even the hard-core is going to listen at even to show off the system. Even then... I'd say about 1.5dB of compression in a small midwoofer isn't bad.

How much of this is power vs. BL compression? I don't know... the test doesn't deviate between the two.