Linkwitz Lab LX521 Dipole Loudspeaker Project - Page 3

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Construction log - continued from page two

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Primer and Paint for the Woofer Box [May 6, 2013]

<--click any picture to enlarge

I intend to experiment with some new (to me) primers and paints. These are commercial paints, and probably not available at most retailers. I purchased them from Homestead Finishing. The owner is Jeff Jewitt, for those of you who know of his books on finishing. The cost of these gallon cans of paint is high, but if they provide the features that I need, they will be worth it.

All are water-based coatings. I do not wish to spray solvent finishes in my garage, and suffer the clean-up hassles associated with them. Being water-based coatings, they will be safer to use too.

I have high-hopes for the primer. I've been looking for a water-based primer that sands easily. I'll have some answers as soon as the weather clears.


Painting Has Begun! [May 8, 2013]

There was a break in the weather today, and I took advantage of it. I had purchased a new Qualspray AM-5008P spray gun from Homestead finishing to use with heavy finishes back in the autumn while I was still working on Orions. I put it to use today for the first time. I needed more tables/platforms on which to place all the small parts. I definitely wanted to get started on the woofer boxes, so they took precedent.

I used the General Finishes Enduro undercoat to spray. I chose black undercoat because that's the color I'll end up using. No sense trying to hide white undercoat with additional layers of black finish. I used the Enduro undercoat straight from the can - no dilution. It sprayed well using the 1.8 needle/nozzle @ 29 psi at the gun's regulator. The GF Enduro undercoat smells just like their water-based Milk Paints. It's a little thinner though, for ease of spraying no doubt.

During the weather-induced downtime, I had used some Bondo spot putty, an automotive product, to fill in any obvious divots or flaws. It comes in a tube and is available at most auto supply stores. In some places, the wood itself was a little rough - almost wash-board looking for whatever reason. I had put on a wash-coat of shellac earlier, so perhaps that caused the wood surface to react. This Baltic birch wasn't the best sample I've worked with.

Painting the outside surfaces of the boxes was easy. The gun lays down paint quickly so I could easily maintain a wet edge on the large areas. However using the gun on the inside recesses of the woofer housing produced bounce-back spray. I wore an old pair of glasses, and I'm glad I did to prevent paint spray from spattering my good glasses. I wear a respirator even though it's water-based paint because there's much more than just water in the spray.

Overall, I was very pleased with the first painting session. Keep in mind that it's just primer and painting becomes more difficult while finessing top coats. I'll have to spot putty a few additional areas, especially the cut ends of the plywood. Once things are painted black, the minor flaws become much more visible. It's all part of the finishing game, and the appearance improves with each new coat.

I'll start sanding after the second coat goes on. Wood-grain texture still shows, and additional applications of primer together with sanding between coats will level it out.

Clean-up of the spray gun was easy. I had previously filled a bucket with fresh water before painting, and used it to fill the spray-gun's cup for cleaning. I tossed the cap in the water, and I sprayed a minute's worth of plain water through the gun to clear most of the paint After that, took it indoors to disassemble it for a thorough cleaning.

The major "dimples" in the finish will need attention beyond just primer. They will be filled with some Bondo Spot Putty, an automotive product, and then sanded flush with the surface.


Damping the Bridge Uprights [May 14, 2013]

As I had mentioned before, the bridge upright panels rang surprisingly when they were rapped with knuckles. I doubt that much acoustic energy will make its way to the uprights to excite them, but just in case, I did an experiment. It worked, and it will be part of my build just in case.

I had ordered two pieces of 0.030" thick steel sheet that measured 12x24" from McMaster-Carr. I took the sheets to a heating/cooling company to have them sheared into 6"x18" pieces to line the back of the bridge upright panels. RTV silicone adhesive is spread between the metal and the wood.

It might appear strange to use metal to damp sound, but I've done similar things in the past -  successfully. Both the wood and the metal have differing natural frequencies, and when they are firmly combined together, neither can resonate normally. Once piece wants to vibrate at one frequency, but it's tied to the other piece that doesn't want to move in the same way. It's essentially a system with two different spring rates tied together with the rubbery adhesive acting as a damper. 

I desired a thicker sheet of steel than what I used, but two factors made that less attractive. I know that industrial foot-operated metal shears can handle up to 20 gauge steel - about what I ordered. Thicker steel would require more powerful shears and I wasn't sure that I could locate anyone with that capability. Second, the thicker the metal, the closer to the woofer box the sides become. The gap is narrow now, and I didn't want to approach the point where accidental contact between bridge and woofer box could happen. If I had planned to do this before cutting wood, I could have used thicker material, but I'd have to order it from a supplier offering custom cut sizes. A quick search found a place called Metals Depot that cuts to order.

After I drew the hole pattern for the mounting screws, I used a Whitney Jr. sheet metal punch for the holes around the periphery of the metal, and drilled the hole located at the center of the sheet. The punch wouldn't reach the center. After the holes were made, I used a small countersink bit to let the flat head screws seat a little closer to the panel. I didn't want them protruding much toward the woofer box. I gave the pieces of metal a quick paint job with Krylon spray paint from the can. That should protect the steel from surface rust later on.

A toothed spreader was used to provide good adhesive contact between the metal and the plywood. After using the screws to clamp the metal to the plywood, I pressed down firmly on the other areas to make sure that there were no gaps underneath. Upon lifting the completed panel, it was obvious that I added mass to it. There's noticeably more heft to it than before.

I need to get to the hardware store tomorrow to get enough additional adhesive for the remainder of the panels.

The silicone is just now curing, but a preliminary knuckle rap test shows the resonant frequency to be lower in pitch, and to damp out faster than before. There was a noticeable difference between the damped panel and an undamped one. I will try again tomorrow after the adhesive has cured to determine any further changes. I expect damping to get better as the adhesive becomes firmer.

I made a short video showing the "knuckle rap test" comparison, but decided not to consume internet bandwidth posting it. You're going to have to take my word for it.


More Painting and Uh Oh! [May 15, 2013]

I've been adding more coats of primer to the woofer box and the small parts. It was looking fairly good.

I also finished adding the damping materials to the bridge uprights - a task that I started yesterday. I had to fetch more silicone adhesive from the hardware store to complete that work, and it went well.

Then I managed to snatch defeat from the jaws of victory with the most recent coat of primer. I have something that looks like micro debris showing in the paint (now dry). When applying wet finish, it almost appeared there there were hundreds of little "bubbles", each about 0.02" or 0.03" in diameter.

Disclaimer: After spraying, I always remove the cup from the gun, disassemble the nozzle and cap from the front to clean the gun and to remove debris. I use a toothbrush on the parts that I can reach. Clear water is run through the gun to flush paint away, and one final burst of compressed air blows out the remaining water before I put it away. The pre-paint precautions were the same today as before - strain the paint through a paper funnel strainer into the gun's cup to prevent particles from being sprayed. In the cup there is a another small, wire-mesh strainer installed as a backup.

However when spraying this coat today, it was obvious that the finish was going on with problems. The air line has a filter too, so I'm at a loss to explain what caused these very small "pimples" on the painted parts. The last picture in this group shows an extreme close up on the problematic finish. I wonder if something happened chemically to the finish? Was the box outgassing in small, local areas because of temperature/humidity swings and "blowing bubbles? And things were going so well.

In the meantime, I'll sand them like a madman and try again. Thunderstorms are predicted for the next several days, but I might be able to work around them.

Maybe I should have veneered the boxes!

Edit: I found that bubbles in a water-borne finish are evidence of an excessively heavy finish in HVLP equipment. Even though I have a conversion gun, I'll try lightening the coat a bit. Thanks for the internet!



Rain, Rain, Go Away [May 17, 2013]

It's been too damp to paint, so I tackled the assembly of the bridges. I had planned on using pocket screws alone to hold the sides to the top, but I felt that wasn't going to be enough support. I went to the hardware store and bought some 1-1/2" right angle brackets, and a box of #8 x 5/8" wood screws. I didn't really want #8 screws, but the brackets came with countersunk holes for them. Smaller #6 screws slipped through the bracket holes. Using larger #8 screws certainly required drilling pilot holes for them, and that meant some precision was in order.

I butted the top of the uprights against a right-angle jig to position the brackets, then carefully marked, center-punched, and drilled the pilot holes. It took time and care to do, but it wasn't difficult.

Part of the flat heads of the #8 screws protruded below the sheet metal bracket and prevented effective tightening. I lightly countersunk the wood located under the bracket holes to provide space for the bottom half of the screw head to fit. This allowed the screws to seat fully and sit flush against the bracket.

I also cleared the partially obstructed pocket screw holes and gently countersunk them to provide a space for any "burrs" pulled up by the screw threads. This helps to get a strong, square seat, without any burr of wood trapped between the two pieces. I used 1-1/4" long, fine-thread Kreg pocket screws for this fastening task.

Both bridges went together well, and are much more stable side-to-side than I would have guessed. I suspect that the combination of pocket screws and the brackets is responsible for the strength. I suspect that either of them used alone would produce a less secure junction. I should not have any structural wobbles when they are playing.

Both bridges look nice too, enough so that I took them into a living space for a work-in-progress cameo shot. I'm very pleased with this aspect of my LX521 project.

I'm a little concerned that the exposed screw heads on the damping panels may contact and mar the paint on the woofer box when the bridges are lowered into position. I intend to buy some self-adhesive felt strips from McMaster-Carr to cover the screw heads and prevent paint damage. The metal brackets could also contact the woofer box paint when the bridges are slid into position, so they'll be treated similarly.

Update: The weather, while not perfect, changed enough to be OK for painting. The morning fog burned off, but it was still very humid in the afternoon. Because I am merely adding primer at this point, I was not overly concerned about perfection. I just need a fairly smooth primer base for the paint, and sanding primer coats is going to be part of the process anyway.

I did not have the painting problem that occurred a couple of days ago. Paint went on smoothly - well, smoothly enough for garage painting.

One of the hazards of garage painting is the presence of unwanted critters. Here a bug found it's way to the wet paint, and left a trail of footprints. I used needle-nosed pliers to remove him after taking his picture. I'll have to sand that area a little more than the rest before the next coat of primer.


Decision about Paint Color [May 18, 2013]

I've mixed two custom batches of General Finishes Milk Paints in an attempt to find a shade of red that works well with the cherry baffle. Neither blend worked out. The first experiment used a lot of Lamp Black mixed into Brick Red, but it became very deep, brownish purplish - and not very attractive (not shown here, it was that bad!).

The second mix used much less black, and I ended up with the red color shown in the top picture here. The trouble is that while it looks great against a black item, it clashes with the color in my cherry baffles. It's not the most attractive combination.

The red color shown, for my own recollection later, was made by mixing 85ml brick red with 10 ml lamp black. I added 3 ml of distilled water to the paint mix to thin it for spraying.

I've decided to just paint these parts black instead of trying for a color that works with cherry. Basic black is boring, but it will work. The black shown in the lower picture is just primer, but it lets me see the color combination.

The M4 x 8mm screws thread into the back of the opposite-facing tweeter. The self-threading screws fit into pilot holes that I've already drilled in the baffle. Together, they should clamp things together tight enough to prevent buzzes and rattles. I hope.


More Putty and Primer [May 19, 2013]

It won't be long before I can quite primering, puttying, and sanding and to begin painting a finish coat. The surface of the woofer boxes is getting very smooth. Most of the wood grain is being filled in. Stubborn spots get an application of quick-drying spot putty, and are then sanded flush. The 320 grit Abranet sanding mesh mounted in the random orbital sander takes just seconds to level an area once the putty dries. [As long as the sander can reach the spot!]

I intend to use General Finishes Enduro water-based primer again on future projects. I like it. It dries quickly, cleans up easily with water, and sands nicely. It dries a very flat black, but the first touch of sandpaper makes it gray so it is easy to see where I've been. The only drawback is the black dust that gets everywhere from overspray and from sanding. I'm in a garage, so I'm not too concerned. It would be nice to have a dedicated painting area though, especially if it is separated from the house. I've been tracking the black dust into the kitchen when I need to fetch something from inside the house. This undercoat also comes in white which should make the dust less offensive. For an up-charge, you can have it custom tinted too.

While the primer dries to a very flat finish, it still shows a sheen in glancing light. I will probably begin applying topcoat paint after one more coat of primer. And one more sanding. Today's application is the 5th coat of primer. The boxes are looking very nice, and the 6th coat of primer will be a little insurance for when I get into the glossier paints.

I will not try for gloss inside the box - maybe a satin or matte clear coat. I might even use satin finish on the outside too depending on how well things progress. Glossy is such a labor-intensive finish, and reveals the smallest flaw. It can drive you crazy.

I retrieved an earlier picture of the Baltic birch surface after its initial coat of primer, and added a current photo of the same area after five coats of primer. You can see that the wood grain, so prominent after the first coat, has disappeared after all the work. There's much sanding between coats, and that takes more time than the painting itself.

The end result should be a smooth finish, regardless of whether I choose satin, glossy, or something else.


Testing Fit and Finish [May 21,2013]

I placed another order with Homestead Finishing for some Enduro clear Poly in satin to coat the inside of the woofer box, and possibly for the outside too. In the meantime, I decided to do a stack fit of the parts to determine how a non-gloss would look compared to the high-sheen semi-gloss of the wooden parts. It was also a test fit of the bridge to woofer box. The fit passed with flying colors.

I like the appearance even now, and could live with a matte finish similar to the black Enduro Undercoat primer that you see here. Even matte looks tidy. I will add paint and clear coat though - the primer is way too soft as-is. Satin is easy to do, and will take the sheen up a notch.

I did order some very fine 800 git and 1000 grit Abranet sandpapers for my random orbital sander, and Menzerna German-made polishing compounds for the achieving a high-gloss on the woofer box exterior if I choose to do that. I now have options to consider.

I must confess that with the end of this project in sight, I am getting a little impatient with all the finishing steps required.


Paint, not Primer - Finally! [May 26, 2013]

My plan is to spray some glossy black that was meant for the Orions, then to topcoat that in a satin clear coat. The final coat determines the sheen of the surface, so the glossy sheen of the black being applied now doesn't matter - except for the color. It's a good test of spray painting skills too because every little problem shows with a high-sheen paint. I managed to get three coats of the glossy black sprayed in the last two days.

It's building slowly. I applied one coat to everything yesterday. Today I began by sanding [which takes a couple of hours to do all the black parts], and applied two coats of gloss black with a minor scuff-sanding between them. This waterborne paint takes a few hours to dry enough to sand.

I used a smaller 1.5mm nozzle/needle on my spray gun because the paint is much thinner than the primer used before. Because it's thin, it thereby must be applied thinly, I've discovered that this thin paint telegraphs sanding scratches if they are deep enough, so I've moved up to finer 600 grit Abranet sanding disks.

Painting inside the box is difficult. There are all sorts of blind corners into which I want to paint, but much of the spray comes bouncing right back at me. There's no way to get the desired right-angle spray direction onto some of the interior surfaces, and I'm getting a lot of overspray landing on some interior panels. The last picture in this group shows the gritty appearance of overspray on the front baffle - the most visible one! I'll explore ways to get around that problem, but in the meantime, it means more sanding to smooth it out. By the way, the photo was made while the paint was still wet, so it won't look as bad after drying.

I have two turntable-bearing support surfaces to hold items to paint, but I wish that I had more. The little pieces are merely resting on empty cardboard boxes, and getting around them to spray edges is not easy. It's also difficult to see when the light isn't glancing at the correct angle.

I will build several more coats of the glossy black before I switch to the clear satin topcoat.

I'm fighting weather a bit. After the storm system that left Moore, OK in ruins passed though here, we had several days of rain and high wind. Thankfully, nothing in the way of damaging weather, but enough wind, rain, and cold temperatures to postpone painting. There is some rain forecast in the next three days, so I might be working around that. That's all part of the garage painting "game".

By the way, the gloss black paint is actually a General Finishes Clear Poly topcoat with black colorant added into it. The gallon bucket was ordered from Homestead Finishing and custom mixed there at the suggestion of Jeff Jewitt, the owner.


Another Decision About Paint [May 28, 2013]

Looking at the gloss black paint on the bracket made me reconsider my initial choice to go with a satin sheen on the bracket (not the woofer box!) The glossy paint, although not glass smooth, looks very fine. Waterborne paints never achieve the gloss that solvent lacquers can provide off the gun. If you want glass smooth with waterborne, you must rub it out with abrasives. However, I thought that this sheen looks very good as-is, especially for just a bracket.

I thought that I could do better on the finish, so these were sanded after the photos were made, and another coat was applied. I got one #@& run in the paint. I'll sand that again, and maybe the third coat will be OK. I see a faint telegraphing of the plywood layers through the paint on the bracket in certain light. I don't know if that will ever go away because of the differential expansion and contraction of the wood layers, depending upon their orientation. I'll certainly see if more paint helps though.

Being somewhat impatient, I just thinned some GF Lamp Black Milk Paint [200ml paint:14ml distilled water] and painted the crossover mounting pieces and the tweeter sub-baffles. One coat, and they look good. They are done.

The woofer boxes remain the biggest finishing task ahead. They were sanded yesterday after the first coat of black gloss. It was too windy today to tackle painting them, so they await in the garage for a calmer day.

By the way, the hex bolts on the front of the brackets shown in these photos prevent the internal 1/4-20 threads from becoming fouled with paint. The bolts will be tossed when the painting is done.


Crossover Work [May 29, 2013]

I added a coat of paint to some items today. While the paint cures awaiting some sanding, I experimented with mounting of the passive crossover components. I knew the general direction that I wanted to take, but as everyone knows, the devil's in the details.

I was a little concerned about vibration of the electronic parts against the bracket, so I used some self-adhesive felt to damp vibrations. On the capacitor, there's a 1/2" strip adhered to its side where it comes in contact with the crossover mount. I also put three dots of the felt on the bottom surface of the cap where it rests on the mount.

I flattened the coil bobbin flanges on the bottom where they contact the mount to prevent rolling, and used a cable tie to bind it tightly to the mount.

The fit inside the bracket is very tight. I had attempted to cable-tie the upright capacitor to the mount upright, but the extra width prevented the assembly from fitting inside the bracket. I removed that cable tie.

I tried two dots of felt on either side of the cap to bear against the bracket sides, but even 1/16" felt was too thick. I might revisit this and place the felt dots further around the circumference to reduce the total profile.

The crossovers should look very tidy when finished. All the wiring connections will be placed under the crossover mounts and be out of sight. Wires to the drivers will emerge vertically at the opening that remains between the crossover mount and bracket.


Waiting to Clear Coat, and Decorative Time Wasting [June 1, 2013]

The last coat of glossy black paint has been applied. The woofer boxes are suitable for use as-is, but I want to clear coat them with a satin finish. The "glossy" paint is more of a semi-gloss, and looks a little "brassy" on large items like these boxes. There's much wind today, and storms are forecast, so I have to wait a day or two. I am pleased with their appearance so far.

In what might be the biggest time-waster in diy audio, I chucked up the connector bolts in my drill press, and sanded, then polished the heads of them to a high sheen. Ordinary connector bolts work just fine, but they look rough and industrial with their dull, burr-laden heads. In the drill press, I started sanding with 220 grit wet-or-dry silicon carbide sandpaper, moved up to 400 grit, then used Happich Simichrome polishing paste on the heads to produce a near-mirror finish. Then I used some gun blue paste on the shiny metal, 3 coats, to produce a black-chrome appearance. This work took about an hour for 8 screws.

The blued-steel heads, if left unprotected, will rust very quickly. I used some Sheath Rust Preventive to apply a coating to them. It's essentially a wax dissolved in solvent. When the solvent evaporates, the wax coating remains behind to reduce rusting. If I didn't have this particular product, I'd look at Boeshield because of its stellar performance in published corrosion tests.

I must admit that this is certainly not essential to the sound or structural integrity of this project. It's merely mindless work that keeps me occupied while paint dries.

I still have to test the ASP boards and install them into the case. I still need to complete the passive crossover wiring.  I probably should be doing that work instead of decorative work like polishing screw heads!

I observed something curious when I was close to the bracket for this photo in streaming sunlight. I noticed the the black paint has many thousands of tiny flakes embedded within it. It reminded me of a 1960s metal-flake paint job, except on a much smaller scale. If you click on the next-to-last photo in this group to view it larger, you'll see what I'm talking about.  The photo almost makes it look like a rough surface, but it is completed embedded within the coating and it shimmers as you move your head around. I noticed that the light source must be very specular - like direct sunlight - to see it.

Like my nephew says...Cool!


Update: I did not clearcoat the woofer boxes. I decided that the gloss black finish looked good enough to stand on its own. It's more of a satin than glossy anyway.


Wiring the Tweeters [June 2, 2013]

The weather continues to delay the final spraying of clear coat on the woofer boxes, so I spent time wiring the tweeters into the baffle. The work was a bit delicate because of the two tweeters and two sub-baffles that must be coordinated. A spatter of hot solder flux in the paint wouldn't be appreciated either.

With lots of paper towels and an old carpet remnant to protect items during this work, it wasn't difficult. I went slowly and very carefully not to spoil work that had already been done in finishing.

I used Radio Shack 24-gauge speaker wire for the tweeters because they will see very little power. It also provided the flexibility needed to bend into tight spaces. The 24-gauge wire runs for only a couple feet, then attaches to a more substantial wire located in the space under the crossover, so the effect of light gauge wire is inconsequential.

Before tightening the tweeters, I rotated them to orient their hex grids horizontally for appearance's sake.

I also began soldering wire in the crossover assembly, but there's not enough work done yet to warrant a picture. I'm awaiting a hot knife tip for my ancient pre-1964) Weller soldering iron to neatly trim the Techflex braided cable sheathing that I intend to use over the wires.


Productive Days [June 3 & 4, 2013]

With most of the painting out of the way, I'm making headway assembling the speaker.

First, I installed 2" x 1/8" synthetic felt strips inside the bridge to cover up the screw heads on the damping metal. This prevents the screw heads from making direct contact with the finish on the woofer box. It probably adds a little more acoustic damping to the bridge too. I'm sure that this bridge is very acoustically inert compared to other methods of construction. The bridge sides ring much less than the baffle itself does, so it shouldn't contribute to unwanted resonances.

I also installed the drivers into the baffle using #6 x 5/8" self-tapping screws (upper midrange) and #8 x 5/8" screws (lower midrange). Nothing fancy. The fit nicely into the predrilled pilot holes done months ago before the finishing steps began.

I attached the baffle onto the bracket using 1/4" x 1-1/2" machine screws. They engaged the brass inserts placed inside the bracket before it was assembled. I also placed a gasket of very thin polyethylene foam between the bracket and the baffle. I had purchased a huge roll of the stuff for my Orion project to place between the sides and the baffles, but never used it. This was a good application for it.

There was a short moment of panic when I realized that the connector bolts that I had so carefully polished would not install because of the short space under the baffle. The solution of course is to loosen the baffle screws first and shift the baffle forward. That provided enough room for the bolts to drop into position. I'll use an Allen wrench to tighten them (the screwdriver tool won't fit), but it is one design item that verges on a mistake. I wish I could foresee all the issues completely before I start fabricating parts.

The wiring of the drivers was started. I wanted the wiring to be unobtrusive. There are some baffles that are machined to hide wires, but it's difficult with a solid wood baffle to do that. I believe that the routing of wires combined with a 1/4" and 1/2" Techflex looks tidy. It's not completely done because the crossover shuttle still needs to be incorporated. It's installation will route and hide wires further.

It has been a productive couple of days.


Crossover and More Baffle Wiring [June 7, 2013]

In response to a comment about the wiring potentially shading the sound from the rear of the woofer, I slightly rerouted the cabling to position it behind the spider ring casting. It took 3 cable ties to get the wire into position - one tie placed fore of the ring, one aft, and then the tie for the cable itself looping into the other two. It places the speaker wire bundle almost completely in the "shadow" of the spider, leaving the area around the cone mostly unobstructed. At this point, I'm not that concerned. After all, photos of SL's speaker show wires routed in a similar fashion. The first photo of this group shows at least two of the ties at the affected point.

Next up was tackling the crossover shuttle. It was slow going, and in a way, like building a ship in a bottle. There's very little room to position wires inside, and the terminal strip could hold only two heavy-gauge stranded wires at a time. I'm using Madisound's Supra Classic 15 ga. speaker wire. Even though I had punched the wire holes larger for this, the openings were still too small. I had to get creative with the connections, and it became a combination of wire-to-wire and the terminal strip.

It was also awkward because many of the connections had to be made while the crossover was near its final position on the speaker. I had to prop it up using a book in order to work on it.

Once the bottom of the crossover was screwed into place, and the assembly inserted into the bracket, it became satisfying. I still  have a little more work to do to route the wires from the speaker more compactly so that the crossover shuttle can sit a little more into its cavity. It still looks tidy though.

I also attached the 4-pole Speakons to the pigtail coming from the crossover, although I have no photo of that yet. It looks as if the main part of this speaker is 99% assembled.

I need to route the cabling in the woofer box and install the woofers, and tend to some long-delayed ASP tasks, then it will be completed.

I'm a little worried about the ASP and what happens with a mains power outage. With the Orion, cycling the ASP power when the power amplifier was on could blow drivers. Here in southeastern Ohio, power glitches are a way of life. Hardly a day goes by without the uninterruptable power supply for my computer kicking in because of a transient glitch. Last week, I was without power for half a day, and last summer, for a week in June. I will probably obtain another battery backup UPS unit for the ASP to keep it powered while the amps are left to the mercy of the power company.


Wiring the Woofer Box [June 10 & 11, 2013]

Before I began wiring up the woofer box and attaching Speakons, I researched the wire positions in the cable to see which combinations produced the least crosstalk between the tweeters and the mids. SL warns about this in one of the OPLUG posts. One member named Drew measured the crosstalk between different pairs of wires in his 8-conductor cable, and published the results. However, the Parts Express 8-conductor wire that I used differed in the color coding of the pairs. I made a chart to correlate it to Drew's sample.

The Speakons have numbered connectors for the wires - 1+, 1-, 2+, 2-, etc. The Speakons mounted at the top of the box had four connectors for the two pairs of wires for the tweeter and mids. The 8c Speakon in the bottom had more connectors of course, and the number included 3+, 3-, 4+, and 4- in addition to the numbers found on the 4c Speakon. I decided to make the tweeter the 1+ and 1- pair, the midrange 2+, and 2- because those numbers are common to both connectors. Because this was in the order of descending height, I carried that convention through to the two woofers on each side. The bottom woofer was thus numbered 4+ and 4-. This system keeps the same numbers for the tweeter and midrange on top and bottom Speakons to prevent confusion when attaching wires to them.

I have the wiring on the right woofer box almost done. There will be left-hand and right-hand boxes, with the Speakon connector positions mirrored on each. I had drilled the wire access hole for the top woofer mirrored too, planning this from the beginning. It will help with the cable runs in the room. The woofer box on the right side, for example, will have its Speakon on the right side of the box, positioning it closer to the right wall. The speaker cable won't intrude into the room as far to connect to the speaker.

I used Wood Artistry Speakon brackets sold for Orion speakers for a clean appearance. They are black anodized aluminum, and that fits nicely with my color scheme.

To attach wires to the Speakon connectors, I used crimp terminals that slip onto the connector's spades. The space for connections is very limited, and there are no holes in the spade terminals into which to hook wires for soldering. The internal speaker wiring I used was the Supra 15 ga. speaker wire sold by Madisound. It has a fairly stout conductor, so crimp terminals appeared to be the best way to attach wires without mistakes. I did wrap electrical tape around the inner group of connectors (all of the the "+" polarity) to reduce the possibility of them touching/shorting the outer group ("-" polarity). However, the mechanical integrity of the connections is good, and it would take a fairly hard blow to force the connectors to touch even without the tape.

I'm using mostly 1/2" Techflex to bundle the 4 separate pairs of wires running into the box. It looks tidy. I was very pleased when it stretched enough to enclose the terminals on the rear of the Speakon.

I also installed the 4-pole Speakon on the top of the woofer box. This allows for a quick and foolproof way to electrically connect and disconnect the bridge assembly.

On another note, and one that is not as happy, I'm having a little trouble with my ASP circuit boards. The initial check for +/-12 volts worked fine on both boards, but after stuffing the op-amps into place, I encountered trouble. The gain numbers for each stage, except for the midrange, are significantly off. I ordered some connectors to be able to run ARTA with my sound card to assess the condition of the boards, but failing the spot checks was disheartening. I had no trouble at all assembling Pluto and Pluto+ circuit boards, so I'm in unfamiliar territory right now.

I'm mechanically inclined, but I'm not a sparks and wires wizard.

[UPDATE: This issue was quickly ironed out after learning ARTA software. The culprit was two missing resistors, one per board, that were not on hand when I stuffed the boards. I had forgotten about not having the resistors, and that they were missing. A thread describing the troubleshooting is posted in the LX521 Resources area of the OPLUG. The thread is titled ARTA testing of ASP . Note that this section of the web site is available to owners of LX521 plans, but not to the general public.]


The Woofer Box [June 12, 2013]

The woofer box should be called the "black hole" for a couple of reasons. Like a black hole, the gravity around those massive drivers is profound. They are very heavy. Next, any tool that comes within 4 inches of the magnet gets sucked right to it. I had to be very mindful of that while working. Finally, it's very, very black inside, making visibility poor for seeing black fasteners, attaching wiring, and even photographing. The exposure range from highlights to deep shadows exceeds what my camera can handle. My old eyes are even worse.

I installed the drivers by myself, and found that laying the box sideways was easiest. For me, installing the top woofer was easier than the bottom one. I took advantage of the access port that I installed into the top of the box, and that helped for securing fasteners for the top woofer. The port's job is done.

I used 8mm quick-connect terminals from Madisound for attaching the wiring to speaker terminals. The wires were crimped onto the connectors, then soldered to them for an extra secure joint. The connectors were then pushed onto the woofer lugs. They look very secure. I'm glad I did it this way because a soldering iron would certainly have been drawn to the magnet, resulting in melted spot(s) on the rubber boots.

I have one woofer box completely done, and the other is scheduled for tomorrow. This one is sitting under the left speaker right now, and it looks very handsome. One speaker is done.

I dread lifting the woofer boxes up the stairs for a photo session once everything is complete. They are truly back-breakers.

Update June 13: The other woofer cabinet is now done. That completes the non-electronic part of this project, and I'm very pleased with how they look. Wife says they have personality. Keep in mind that she likes my Plutos, and was elated when I said that the Plutos may be moved upstairs to the TV room.

She also looked at the inductor on the back crossover, and wondered what the "roll of tape" was doing there. I had removed the Madisound masking tape wrap and replaced it with a nice, white Tyvek wrap to hold the coil of copper wire in place. It was an effort to make the the coil look a little better, but if she's thinking it's roll of tape, I missed the mark!

Now it is back to work on the electronics...


Some Photos [June 14, 2013] and Listening Impressions [June 21, 2013]

As always, click on any thumbnail picture to get a larger view.

It's difficult photographing these in a small room. In order to convey texture and sheen, the lights almost always need to be positioned where walls and furniture are in the way. The heavy speakers, each in two parts, aren't easy to shove around either.

Already, there are things that I'd try differently next time...

  1. I'd add paperbacked veneer the top of the woofer boxes to prevent telegraphing of butt joints through the paint. A few faint lines are now evident where the pieces are joined because of humidity-related expansion/contraction. Thankfully. because the boxes are black and mostly hidden by the bridge, you have to look hard to find them.
  2. I'd probably install the baffle screws from the rear in the next build. I'm not crazy about the appearance of the four 1/4-20 flathead screws that attach the baffle to the bracket now. But it's not a big deal.
  3. I'd make the baffle bracket rotatable. It's becoming clear that being able to toe-in the baffle compared to the woofer box allows valuable acoustic tuning in the room.
  4. I spent nearly $60 for the #10-24 black locknuts for the woofer mounting screws. That's crazy-expensive, and something I'd revisit. I hit "Buy" in a weak moment. Also, their turning resistance made spinning them down slow. I had to use tools all the way down. But they look nice.

And some things that I'd not change...

  1. The small screws securing the tweeter sub-baffles don't bother me at all - probably because they are black-on-black.
  2. I'd continue using Techflex on exterior wiring on rear of the baffle. The Techflex braid sheathing looks very professional. Inside the black woofer box, the Techflex-covered wires blend right in.
  3. The milled chamfers on the bracket and wooden bridge pieces add a feel of finished woodworking. Chamfers or roundovers are easy to cut using a router, and a little time spent here adds significantly to the appearance.
  4. The paints and wood finishes I found are ideal. If anything, I might spray a clear satin over the semi-gloss black on the woofer box to reduce visibility of small flaws. However, I don't have much to complain about right now. The flaws are very small, and better than what I've seen on some commercial loudspeaker offerings.
  5. I like the Wood Artistry Speakon brackets. It's a good product. I'd also continue mounting them mirror-imaged left and right on the two speaker boxes. I think it makes for more tidy wiring inside the box, plus I have the connectors and speaker cables closer to the walls.


My first impressions are:

  • They need no subwoofers. These loudspeakers dig deeper than I ever expected they would. I usually take "no subwoofer needed" statements with a grain of salt, but there's no mistaking the bass authority delivered by the SEAS L26RO4Y drivers in the bottom. Color me surprised - and pleased.
  • They image nicely. The sweet spot in which to listen is a bit smaller then for my Plutos. There's less room to move left or right before the soundstage collapses. My listening room is narrow though, and I'm unsure about how the soundstage would fare in a more ideal space.
  • While the Plutos are no slouch for quality music reproduction, there's much more "micro-detail" apparent in the sound of instruments in the LX521. I suspect that the high-quality of the SEAS drivers contributes to this. It doesn't hurt that many of the drivers were custom engineered for the LX521. The low-cost AURA tweeter of the Pluto is likely its Achilles heel. I'm very pleased with the fine detail delivered in music with the LX521 compared to my Plutos.


I've added more listening impressions below after listening to them for a few days, and after doing some experiments with positioning. However my listening room is not ideal. The next section explains why. Consider it an important preface before diving into my subjective impressions.




Speaker Placement and My Room's Limitations [June 28, 2013]

The LX521 speakers are heavy, and are comprised of two components which makes moving them cumbersome. I made a pair of flat dollies using some inexpensive Lowe's casters attached to 16"x19"x3/4" MDF. Placed under the speakers, I could easily experiment with speaker positioning.  I considered making the dollies a permanent accessory, but they lift the already-tall speaker by another 2" to 3". In my low-slung Ikea Poang chair, the dolly raises the speaker so that the bottom of the lower midrange driver is at my ear height. By raising up a few inches from my seated position, the sound gets better. This indicates that the dollies won't work long-term. Or I need to modify my chair.

I'm finding that placement for ideal sound is going to be a compromise in my listening room. It's the largest finished room in the house, and it's still not quite wide enough with the current furnishings in place. Being located in the basement, my ceiling is also 5" lower than in a normal room.

The picture on the left shows the current configuration. Some furniture is higher than other pieces, so I coded their relative height with gray tones. White is at floor level, black is at the ceiling, and a percentage of gray is in between. Taller furniture will be shown with a darker shade than shorter pieces.

Linkwitz specifies room parameters to maximize performance of these loudspeakers. My room fails on two key points.

His key specifications are:

  • Lateral symmetry of the loudspeaker and listener setup with respect to large reflecting surfaces.
    I fail this requirement. Click the room layout thumbnail on the right to see my current situation. I listen on an angle to the room.
  • Loudspeakers must be placed at some minimum distance from those large surfaces in order to delay specular reflections by more than 6 ms (sound travels 2 meters in 6 ms).
    I fail this requirement. I've done my best here without moving heavy furniture. In an attempt to mitigate the effects of nearby objects, the right speaker is positioned near a doorway, the left near a fireplace opening.
  • The wall behind the loudspeakers should be diffusive in order to not lose the rear radiated sound from the LX521.
  • The wall behind the listener should be lossy or open.
  • Cloth wall hangings, rugs, pictures, upholstered chairs, open cabinets, plants and other decorative elements are all that is needed to interface a dipole loudspeaker with the room.

All this means that I cannot hear this speaker at its very best in my current room. However these speakers still produce an overall sonic improvement over my Plutos. I am sure that I lose a little imaging precision because of these limitations, but it is still far better than the majority of systems I've heard in other homes.

Listening to the LX521 (Note: see discussion of my room limitations above, and consider their effect on my listening impressions.
Mike Garson's Jazz Hat, Reference Recordings, 2008 - Jazz

The first selection I played was a favorite CD played often on the Plutos. The recording is excellent. There was always a special synergy between my Plutos and this CD. Track 2 in particular is a selection that truly made me appreciate the Pluto speakers when I first built them, and it's a track that I always played for visitors. I wanted to see how the two speakers compared playing it, and it was first up.

Track 2 has some sonics that are a good test of a speaker's performance. The LX521 rendered the saxophone more cleanly than the Plutos, but in my compromised listening room, I believe the Pluto pinpointed the instrument in the soundstage better. My room width, with some intruding bookcases, is too small for dipoles, and I know from reading Linkwitz' web site that this adversely influences imaging. It probably explains why the Plutos held their own imaging-wise.

About seven minutes into track 2, there's a series of taut bass string plucks recorded so well that you can almost see them. The LX521 handled this detail very well. About now is when I start paying attention to the accuracy of the recorded sound, and I conclude that the LX521 renders the fine details very, very well. It exceeds the Pluto in detail, on every track. Everywhere.

The LX521 won on detail, the Pluto for precision pinpoint imaging. I wish that my listening room was about 5 feet wider for a more valid comparison. This reinforces Siegfried Linkwitz's statement that Plutos are nicely suited for small rooms.

Wayne Horvitz, Sweeter Than The Day, Songlines, 2001 - Jazz

This is a very well recorded SACD disk. Track three has some moderately strong bass, and I curious about how well the dipole bass configuration of the LX521 could render it. This is when the LX521 starts to show a considerable advantages over the Pluto. I hear improvements in bass clarity and the LX521 gives up nothing in volume to the two 10" sealed woofers of the Pluto+. Nice! The LX521 pulls ahead of my Plutos on detail and bass reproduction (depth and quality).


Yello, Touch, Polydoor/Universal, 2009 - Electronic

Intrigued by the bass depth that I heard in the previous album, I play a bass-rich recording (track one) to test the dipole handling of low frequency electronic bass. The result was stunning. The LX521 appeared to go much deeper, and played the deepest tones with more volume than the Pluto+ could ever muster.

This was a knockout advantage for the LX521. I replayed track one again just for grins. It is amazing how well the SEAS L26RO4Y drivers can do on subterranean program material. Even though I had planned to add Thor subwoofers in the future, this performance eliminated my interest in building them. That's a bit sad because I have all the parts (two 12" Peerless XLS 830500 drivers, plans, circuit boards, electronic components) to build two THOR subs. However I'm secretly pleased because I was always concerned about the space that two 12" subs would occupy in my room.

I did not judge soundstage with this recording. It is mixed and synthetic, so it doesn't have much in the way of realistic soundstage to evaluate. It was merely bass "candy" to flex the muscles of the woofers.

Andreas Vollenweider, Book of Roses, Columbia 1991 - Electracoustic harp, contemporary/experimental

This is one of the best albums that I own regarding mastering and sound reproduction. This album's genre is a little hard to characterize, but it has never ceased to impress me with how well it is produced. There are some recorded ambient sounds that are played between tracks to tie them together, and they sound very realistic. For example, there are some crows calling in the distance when the disk begins, and they sound as real as the crows that are around my housel.

Track seven features an a cappella track by Ladysmith Black Mambazo. It may be familiar to builders of Linkwitz Plutos because it's included on the test CD for them. It is very well recorded and a delightful test of a loudspeaker on male chorus. There's a dominant singer on the left, with the rest of the chorus centered. The electric harp occupies the right side of the visual scene. This is exquisitely reproduced, and is enjoyable music, not just a test track.

I hope that no "remastering" has reduced the quality of this recording for current purchasers. My disk is quite old now, and cherished.

Giuseppe Verdi, Requiem, Telarc, 1987 - Opera

The LX521 stomps my Plutos on this very dynamic recording - especially on how well it handles the range from low to high volume in some passages. With the chorus singing full volume in Libera Me (track 3, disc 2), and having soprano Susan Dunn raising her powerful voice to be heard above them clearly is spectacular. Parts of the selection are very quiet, then within a few seconds, a crescendo. High volume favors larger driver area, and the LX521 doesn't strain with high SPL.

There are also places where a powerful tympani is reproduced very accurately in this recording. Instead of merely a distant "thud", the instrument overtones are beautifully reproduced together with the bass impact to give the sound its unmistakable realism.

This recording is emotionally engaging for me, and always gives me shivers toward the end of Libera Me.

I have noticed that the recording is still available, but in newer packaging. Once again I hope that the mastering has not been changed because the first edition is a winner.

Phoebe Snow, Phoebe Snow, The Right Stuff, 1995 - Jazz vocal

This is another well-recorded and familiar album. I play track 2, Harpo's Blues, to evaluate a loudspeaker. The LX521 rendered her voice more cleanly than the Plutos did, although the difference is small. My Plutos always added a slight emphasis on the lower tones of the female voice (not just on this album), and the LX521 did not. The feeling that she is present in the room is more believable.

There's a saxophone in track 2 that the Pluto placed in pinpoint precision on the front wall well beyond the speakers, and the LX521 does almost as well. Again, (and in my space-limited room - an important point!) the Plutos did a little better. The sax advances forward from the front wall that is about 10 feet away, and it pulls forward to the left LX521 speaker somewhat more than the Pluto. Certainly this is because of room acoustics. The synergistic combination of the Pluto with this recording was something that worked well, and that's why I chose this album to compare.

I can live with the changed position of the saxophone because Phoebe's voice is so alive and real coming from the LX521.

[Update June 30, 2013]
I have experimented some more with speaker placement, in particular the right speaker that's very close to a large bookcase. When I pulled the right speaker into the center a few inches away from the bookcase, and then significantly reduced its toe-in, imaging precision improved. It now images specific instrument locations in the sound stage just like my Plutos did, but with the improved quality of sound of which the LX521 is capable.

I'm very happy with this improvement, While a having a larger room that meets specifications would have been the best option, this adjustment delivered a worthwhile improvement. The amount of toe-in is now different between the left and right speakers, but it works.

Technically I'm not sure what caused the improvement, but the axis at right angles to the speaker now points toward the open doorway on the right wall, and the nearby bookcase/wall junction is hidden behind the baffle (as seen from the listening position). Perhaps hiding this early first reflection surface behind the speaker helped suppress its influence . It also may help that the major axis of dipole radiation is now painting obliquely down the front of the objects against the right wall instead of being pointed into the nearby bookcase/wall junction.

For another impression of the LX521 loudspeaker, experienced listener Charles Port has a web page describing his findings. His listening room is larger and better suited for these speakers than mine. He can use their full capabilities.


These are better than my Plutos in many ways, and they ought to be considering the difference in cost and size. The sound is more accurate, no doubt due in some part to the better drivers employed. I'm still impressed with how well the inexpensive Pluto+ system held up. In the end though, the LX521 is superior. There's no going back for me.

Bass from the LX521 is better in several important ways than the Pluto+ subwoofer system. First, the LX521 goes deeper, and does so with more volume if that's part of the recorded program material. The LX521 plays bass with better definition too. Some of my impressions about bass may be due to how dipoles load the room resonant modes differently. There should be fewer problems with dipole bass.

Limitations? Yes indeed. There is no free lunch.

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