I'd seen the Linkwitz site many times over the years and always had a curious glance at the Orion pages. As a long-time user of near-field two way speaker systems I did not get how these unusual things with speakers mounted on baffles with no boxes could possibly produce good sound. When a friend mentioned them in mid-2013 and pointed out about a dipole's radiation pattern and the fact that they create a null at the sides I decided to look again.

Spending as much as or more than the cost of a pair of speakers on acoustical treatment of a listening room always seemed like an uncomfortable reality with conventional loudspeakers. With a dipole, not only does a null at the sides reduce the need for acoustic treatment of the side walls but the dipole radiation also reduces the need for controlling room reverberation times. See the Linkwitz site for an in-depth explanation of why this is so.

I ordered the Orion construction plans in September of 2013 but put everything on the back burner for a while. Because of the growing excitement around Siegfried's new design, I decided to abandon the Orion and build the LX521 instead.

Madisound Flat Pack

While I enjoy woodworking, laziness made the Madisound flat-pack very attractive. Shipping was expensive but a quick calculation proved that getting the tools and material needed to build the cabinets myself would outstrip the price of the flat-pack and shipping. No doubt the end result would be better too.

The raw Baltic birch had fuzzy edges caused presumably by the CNC tool that cut the various shapes. Easy enough to knock down with some sanding.

A random orbital sander fitted with 400 grit took the fuzzies off while bringing the surface to a smooth finish. The plan is to use a solvent based polyurathane finish to enhance the natural look of the Baltic birch plywood.

Some small voids were visible on the edges of a few pieces. Easily filled with some water-based wood filler.

I used an HVLP spray gun to apply the polyurathane finish. If you need proof that insects rule the world, try getting a blemish-free coat on a sanded and cleaned piece of wood!

After three coats of finish I began assembly and immediately regretted that I had not masked off the bonding areas. While the idea of finishing before assembly was a way to keep build-up of varnish at the joints, getting finish where the pieces were to be joined was not a good idea. Instead, I sanded these areas as best I could to promote good bonding.

Following this the pieces were aligned and drilled for gluing and screwing together.

The pre-drilled holes were beautifully countersunk.

The two woofer baffles meet at a 90 degree angle but are secured only by the side edges. I used a biscuit joint here to secure this area but it was probably overkill.

The baffles were fitted into the mortises in the side panels to ensure the correct alignment and then glued and clamped into place.

Due to the length of the mortise relative to the tenon formed by the machined edges there is a degree of slop where the fitted piece can slide within the mortise. Part D in the woofer assembly is supported by a rectangular piece of wood from behind but I chose to glue and clamp it to the top of the woofer assembly.

Factory Sound in South Melbourne had 8 conductor speaker cable in stock.

I wanted to hide the speaker wires to the degree possible using the stock Madisound baffle. Some scrap MDF was cut to the approximate midrange driver hole size.

Baffle in position to check the spacing.

The slot cutting bit is fixed at a 14mm depth so the jig is necessary to ensure that the slot won't interfere with the mounting bolts for the drivers. The depth is a guess since I don't have the drivers in hand as yet.

Even with a very slow approach the bit causes some burning of the wood. Should have used a variable speed router.

Seems to do the trick hiding the wires.

With the drivers in hand it is now possible to mark the holes. The mounting hole diameter for the U22REX/P-SL appears to be 208mm.

The information on the data sheet for the MU10RB-SL for an 89mm diameter of the mounting holes looks accurate. The screws will clearly have to miss the tweeter wires that will pass around the perimeter.

A long 1/8" drill bit directed toward the rear of the front baffle allows the tweeter wire to pass though the routed groove to the tweeter compartment.

A manual chuck was required to drill the tunnel for the wires through the midrange channels due to lack of space.

The 1/8" long bit was used again to drill a tunnel from the lower midrange to crossover area.

I had some solid-core PVC covered 20 AWG wire from a tube amplifier build left over, so I gave it a gentle twist and routed it through the groove. So far so good.

Using non-acetic acid curing RTV silicone to secure the wires.

Smoothed with a finger, the silicone fills the channel well.

Front tweeter baffle is positioned over mounting hole with top parallel to the overall baffle.

Area is masked and cut against tweeter baffle's complex bottom shape while sides and top use the straight edge of the masking tape itself.

The varnished surface got sanded to promote adhesion.

PVA glue spread on mounting surface.

Baffle clamped.

Excess glue is easy to remove by pulling up the mask. The tweeter baffles must be attached to the main baffle before mounting and wiring the tweeters. Doing so does not interfere with wiring the tweeters (something that took some time to work out in my befuddled brain).

Proposed by fellow builders - a jig knocked out of scrap plywood to hold the bass cabinet at a 45 degree angle, making it easier to mount the heavy bass drivers.

The jig holds the cabinet in a way that allows the woofers to lie flat. This is probably essential if you are mounting the drivers on your own as it is difficult to both hold the driver and secure it with screws at the same time.

When installing the upper woofer but with the cabinet in this kind of jig, note that when the instructions say to hold the woofer horizontally you will need to hold it parallel to the top surface of the cabinet with the cone facing the top panel. You don't want to try to put the driver in magnet first. As you push it towards its destination the edge of the rubber boot surrounding the magnet will prevent it from entering the hole. Work the rubber boot through the hole gently and the driver will drop into place. It is a tight fit!

Orient the T nuts in such a way that the spikes form a triangle facing away from the driver.

Otherwise the spikes can tear out the wood or even fail to pierce the wood at all.

Madisound thoughtfully provided quick disconnects for the bass and midrange drivers. Using the correct crimping tool will ensure reliable, long lasting yet removable connections. Notice that with a proper tool such as this Molex crimper (#63811-1000) it creates two curled cylinders that grip the wire securely instead of simply crushing them like the crimping portion of your basic $2.99 multi-function tool. The Engineer PA-20 or PA-21 are an even better tool than the Molex. Making crimped joints properly takes practice - see here for instructions on how to do them correctly.

Unable to wait any longer, I threw together the whole system and plugged it into a Yamaha MX-A5000 11 Channel Amplifier. Amazing - the impact of cone drivers with the effortless delivery of a planar dipole speakers. The best analogy I can come up with is that the system is like putting on a new pair of glasses. Things that looked good look even better while flaws stand out in stark contrast. I felt I had heard the future of sound reproduction and the first big advance in speaker design in a long while.

Passive Crossover Mounting Rabbit Hole

Details in the LX521 Contruction Manual regarding passive crossover mounting within the mid/tweeter assembly base don't go into great detail, but Bill Schneider's page has one of the more clever ways of mounting these components securely and in an aesthetically pleasing way.

The usual round inductor can really only fit in a vertical orientation; making use of its mounting hole is difficult within the confines of parallel boards between which the inductor fits with little room to spare. Bill uses a nylon tie to secure it to the sled prior to sliding it into place.

I wanted to make use of the hole in the inductor's bobbin to screw it to a crossover container but what I had envisioned was something I really did not want to create more than one of by hand. Remembering back to when my father used to cast various items using resins I began to explore that avenue. If I only had to make one master that could be molded and cast twice.

Going Digital

From the LX521 FAQ: "Q6 - Are you done with designing the LX521?
A6 - Yes." :)

Midway through my efforts of passive crossover mounting the LX521.4 was announced. I was ready to persevere with the original design especially after my earlier work on the new ASP board. So going DSP was not a decision I made lightly.

But once the miniDSP 4x10 Hd arrived and I loaded the configuration files I began to feel I had made the right decision. Converting the nearly-completed LX521 to an LX521.4 was painless compared to the effort I'd made in getting my version of the ASP and passive crossover built and within a couple of hours I was listening to a markedly better system. For the first time I find myself listening to the music and the recording rather than to the speakers. While the LX521 did indeed render the listening room benign I was still aware that I was listening to a speaker system. Now with the LX521.4 the promise of the room and speakers "disappearing" has truly been delivered upon.

Back to Analog!

April 2017

As we should all know by now, Siegfried Linkwitz never rested. On the 18th of December 2016 he published a circuit diagram for an analog version of a C4-LX521.4V23-2x8V108.xml file loaded into a miniDSP. On 23 January 2017 I built a prototype of the ASP.4 (since I like to lay out PCBs) and on the 26th of that month Siegfried requested it for testing. He made some minor changes to the circuit which he published on the 27th of March 2017.

These changes have been incorporated into a new circuit board and testing concluded on the third design (read the update dated 26 March 2017) "I know of nothing to change at this point, which might increase audible performance." - Siegfried Linkwitz. In June 2017, he asked for some extra boards to do some modifications to. Mike at Hairball Audio sent them to him. Who wouldn't love to see what he came up with?

Update May 2017: Production boards are still available from Hairball Audio. Update January 2018: Assembled units are available from both Hairball Audio and Madisound. Siegfried called Adam at Madisound a "strong supporter" and a "good friend". You are missed, SL.