Modulus-686 and '286 with the Linkwitz LX521.4


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Technical Expert

Has any of you used the Modulus-686 and Modulus-286 to power the Linkwitz LX521.4? A customer of mine is thinking about building such an amp but would prefer to hear from someone with experience with these before taking the plunge. I would love to be able to introduce him to someone with that experience. If you're up for it, please email me. Alternatively, I would very much welcome your experience here. Please say a bit about how the build went and what the results were.

A full-bore system of LX521.4 with Neurochrome Mod-286 and Mod-686 amps happens to be my not-in-this-lifetime dream system. As it is, however, my system consists of the top baffles of the LX521 sitting atop LX-pluses for bass; the latter is the single-driver open-baffle woofer SL designed to add deeper and stronger bass to the LXmini. It uses the same SEAS 10" driver the LX521 uses, but just one instead of two per side.

The top baffles are driven by six Mod-86 units in a ModuShop 3U x 300 x 430 chasis; crossover for these is the ASP.4 from Hairball Audio. The bass units are driven by two channels of an Emotiva A500 five-channel amp intended for home theater; it's the amp SL originally used to develop the LXmini. All of this is set up in much too small a listening space (an attic), which may be why the top baffles sound so great on rather limited power—a 200VA transformer with a Power-686.

If your customer means to build the electronics himself, it's a real plus that the 286 and 686 are pre-assembled modules. It took me quite a while to solder all the parts onto the six Mod-86 pcbs. Somehow I managed to get it all done with only one mistake that required unsoldering a resistor; I'm not at all eager to take on another such product for the rest of my life.

If I were building whole LX521s and my listening space were just adequate but not too large, I think I'd first try wiring the two bass drivers on each side in series and see how they did with the resulting 8 ohm loads each driven by one 686 module. If that turned out to be not enough I'd add another stereo 686 amp to the system and rewire it so each woofer was powered individually by its own 686. If one 686 per series-wired pair proved adequate, it seems to me that would be a less complicated build than a 286 x 4 box with twice the number of input jacks and speaker terminals.

Anyway, I envy your customer. I'm very pleased even with the sound of my own necessarily constrained system, and very much wish I could have the whole shebang!
Yes. Here's an earlier pic that gives a better idea of the space they're in. I took it shortly after I completed the LX521 top baffles years ago. They were still LX521.3 then, and they were sitting on Pluto Plus sealed-box bass units designed by SL. (I called that setup "LX-Tyrion" for Tyrion Lannister in Game of Thrones.) The wall with the chimney is about 10 feet behind the speakers, which undoubtedly helps the sense of acoustic depth.


For me, it illustrates that you can still get a very pleasing result even if you have to make major compromises in some ways.
I like the idea of using the upper baffle with a different sub. The W sub in the LX521.4 has always struck me as incredibly expensive for what you get. $500 per driver and $500 for the amp to drive that driver. Times four for a stereo pair... I can't help but wonder if there's another option for a dipole woofer that would give you (nearly) the same performance for a fraction of the cost.

That said, I have heard the LX521.4 powered by a combination of the Modulus-86 and Parallel-86 and that sounded very good.

Yes, they ARE expensive if you spring for the whole package. My take is that what you get for the money is more of what you need IF you need it, which a lot of people don't, but some do to one degree or another.

Here's what SL wrote about the LX plus (1 driver per side):

Due to the compact open baffle design and the fact that only two instead of four 10"drivers are used, the acoustic output is about 10 dB less than from the LXsub4 woofer of the LXstudio [which is the same as LX521 bass]. This means that the LXsub2 has to be driven 10 dB harder, i.e. the cone excursions have to be about three times larger for the same SPL as from the LXsub4. When using a 200 W/channel power amplifier this can lead to damaging excursions of the 10" driver at very low frequencies...A 50 W amplifier is much safer to use and likely to clip before the driver will. But it will also not allow for maximum excursion at 60Hz.
So if your room isn't too big and you don't need your bass quite as deep or loud you can still get pretty good bass with two drivers and a cheaper amp. Or, you could spend some or all of the money you saved by going with only one bass driver per side on a higher quality amp; just be careful about how hard you push it.

I don't want to stray too far from where this thread started, but I could make some comments about perceived benefits when I replaced my Pluto Plus with LX plus bass.
I bet one could make some tweaks to the XO and also maybe go with a different driver. There are some pretty efficient pro drivers that run with 95ish dB efficiency and can produce some SPL. But that's another project. :)

Apropos, FWIW,'s description of

Open Baffle Subwoofer Flat Pack for 10" Subwoofer (LXsub/LXmini+2) - EACH says,

Used as the +2 subwoofer option for the LXmini speaker kit, and cut for the Seas L26RO4Y. Order quantity 2 if building this design. A single, dual, or multi sub setup with these is a good choice for integration with other speaker systems as well. The flat pack can also be used with other 10" woofers that are suitable for open baffle applications.

Emphasis mine. ;)
There're some pro 15-18" woofers that are excellent for dipole operation as well. I heard a JBL 18SWS1100 in that application many moons ago. But, of course, going that route takes the project from paint-by-numbers to speaker design engineering in a hurry.