The Queen of Blues
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|Brand / Manufacture||Eton|
|Price range||500-1000 Euro|
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Wiegers Duetta Terrazzo
It all started after we moved into our new home.
I have some experience with building speakers, in the past I have build a horn, an active subwoofer and satellite speakers. There was also an unfinished project where I used Polyester mixed with sand and poured into a mold with an inside mold of polystyrene. It was on a summer day in the backyard of my parents house, there was no wind, the neighbors complained about the horrible styrene smell and finally finding out that I was using the wrong initiator that resulted in very high temperatures and in the end a cracked housing…!! Disaster!! They ended up as bird houses in a deserted area of the garden.
Back to now. Recently we moved to a new home and my actual speakers started to annoy me a bit; the high was a bit too “tsssss” and low was basically not really there. It was time for a new project! A big one.
Every project starts with an “investigation phase”, what do I want and what can I do?
The few requirements I had, were :
- Total costs lower than 3000 euro.
- Building it should not be ‘messy’, at least not in my home.
- This project should avenge my disaster with the polyester/sand.
- It has to be a poured Monolith. No wood work.
- High end. Unique shape. Professional look. Has to blend in. High quality sound.
Find help for the areas where I do not have the right competence and workshop/tools.
Soon I found out about the www.LoudSpeakerBuilding.com (www.lautsprecherbau.de) and the hype around Duetta. Surprisingly enough, there was even an Intertechnik studio at only 2.3km from my house. With some initial ideas, I made the step to visit them and found a very nice man called Udo, who enthusiastically welcomed me and even let me borrow the Duetta's so that I had the opportunity to listen to them in my home environment. Perfect! The speakers revealed never heard before sounds and it was a great experience! Not so great was to find out that a lot of my digital music is actually of low quality.
After several days, the executive decision was made to go for a 'Duetta-Einteilig' based design.
With the Duetta I mind I started with the design, with the following considerations in mind:
Standard Duetta design sticks out too far in the room, rotate it and you will even loose more space. Having a cylinder based design will solve this.
- If I want to pour the housing, the power on the molds will be big, however on a circle based design the shape will not deform.
- Eton speakers sound good, but are not that pretty. The yellow/green/gray color is not very attractive and do not match with the rest of the design. Solution, spray paint the drivers.
- The Eton chassis do look different for the 3 drivers. The ER4 is square and does not really match with the rest. And I also do not like speaker designs where you can actually see the screws. This will be solved by placing tailor made black alloyed aluminum rings over the chassis and it should harmonize the general look of the front.
- When the loudspeaker connectors “stick out”, they can easily be destroyed by the immense weight during transport or just moving them around. So I will hide them in the BR opening. Consequence is that the BR opening has to be moved to the back. Good thing is that it is totally hidden and will avoid the speakers becoming a parking place for toys.
In the mean time I did several researches after concrete pouring and mixtures and started to like the idea of a Terrazzo Epoxy mixture more and more. After a visit to an Estrich company specialized in Terrazzo (firma Aman from Beelen), I found myself a good partner for pouring the molds and polishing the speakers. After a discussion with my wife, we decided to go for a white shiny glossy surface with small Terrazzo stones.
It was time for some designing in Sketchup. This program was new to me, but after this project I dare to say that I can draw pretty much everything now in Sketchup.
Initially I started with a diameter of around 50cm, but soon came to the conclusion that the box looked to ‘clunky’ and needed to be thinner and taller. The target volumes for the upper chamber was set to 13l and the lower to 90l.
After a lot of puzzling, the result was a 120cm high speaker with a diameter of around 45cm, cylinder form, but the front cut off to hold the loudspeaker units (depth only 38 cm’s).
This by was my initial paper sketch, soon after followed several versions in Sketchup.
The final design was version10. The ER4 high toner was moved to the middle position so that it is at couch-sitting-ear height, the bass reflex pipe moved to the back and decoration rings added.
The bass reflex pipe will also be poured in and to make the housing even more stiff, I added 2 stiffening rings as can be seen in the detailed 'X-Ray' drawings.
I found out the hard way that Sketchup is not always very accurate with circles, at least not with the default settings. So in parallel I kept an excel sheet to check the calculations for volumes. I made a lot of use of the following formula. Hint, to draw more accurate circles in Sketchup, set the number of 'sides' to 96 for a circle. This can be typed in directly after selecting the circle tool.
Below an overview of volumes, I need around 63 liter of Terrazzo for one speaker.
And here is the plan that I used during the build (the red numbers correspond with the numbers in the upper table).
The outside diameter is calculated with 444,4 mm, (450 mm – 2 * 0,8 mm Steel thickness – 2 * 2 mm Grinding off) In SketchUp I made use of the feature to draw on' layers'. This helps to quickly show/hide specific details.
The skp files that I have created for this project can be found on my profile here on Lautsprecherbau.de. I have modeled the 3 used ETON drivers in the Duetta (ER4, 7_360_37Hex & 11_581_50Hex) for everybody’s convenience. Just import them into your own Sketchup model and you will get a good impression of how your final design will look.
For the molds, I used hard foam (styrodur) that is normally used as insulation under poured concrete floors. This material is very easy to shape, is more fine than the regular polystyrene, can be cut by using a hot wire technique and will be easy to release after the Terrazzo has been hardened. They normally come in plates of 1250x600mm. I got the 30mm and 39mm thick ones (purple and yellow).
The diameter for the outside mold had to be 45 cm and it became clear that this is not a regular size of pvc and after some internet research, I found an alternative in an iron pipe used for air ventilation. The one I got has a thickness only 0,8 mm, height 150cm and has a rim on one side. The pipe is relatively light weighted and requires an additional frame around it to support all the forces during the pouring. The rim will be used to clamp it.
The final total thickness of theloudspeaker walls will be 3 cm. However when the speakers come out of the mold, they will be polished and it is expected that around 2mm will be grinded off to get a super shiny surface. In the Sketchup model this has been taken into account as well, meaning that the inside and outside mold will be 32mm away from each other.
To build up the inside mold I have used a lot of steel. 4 big iron rods to hold all the styrodur plates together; at approx every 30 cm some extra rings and bolts. Since I do not want to drill into the concrete later on, I had to plan all holes in advance. I solved this by using small Aluminum pipes around the steel threads bolted together. Some bigger rods were used to bolt the inside to the outside mold-front plate. This made it relatively easy, I could just stick the 22mm brown plate with the inside mold mounted on it, into the outside mold and fasten it very tight onto the outside. The result was an already very stiff construction. I knew from my past project that the power would be enormous and that the little wooden frame on top of the mold has to avoid the floating.
The opening for the drivers were being made by using a 'Drehscheibe' and guiding it through the hotwire. To cut out the deeper segment I used a drill in a standard with a router head; ground with grinding paper to get the exact deepness.
Due to the enormous weight (130kg each) this little topic could not be forgotten. After pouring it already turned out that it was extremely difficult to just rotate the speakers a bit during the polishing process. It always took 2 people. In the terrazzo workshop we had the luxury of a fork lifter. This is also how we slid it into my Volvo XC60. When it dropped off the last few centimeters of the pallet, the car was directly equipped with a sport package (lowered). On the way back to home, my friend and I had to create an idea of how to get the speaker (we had to drive twice) out of the car at home without damaging it, but also without damaging ourselves (our backs or our pride).
We decided to build a ramp that we could use to slide it out in a controlled way, supporting the speaker on both sides. Once on the ground, we pushed it up and the journey upstairs (floor 3) started on a wheel barrow. Luckily we have an elevator! Once built up, I put some pieces of felt under it and moving it from its place is no problem at all on the smooth parquet.
The filling of the Terrazzo in the mold was done on a huge ‘vibration’ plate so that the air was shaken out. With respect to the mixture I can only tell that it is based on cement and that special additives have been added to make it flow better. To make sure that also the little holes were properly filled, we used small Terrazzo stones; this also leads to less grinding.
On the vibration table, we carefully filled the mold bucket by bucket.
The floating power of the styrodur core was immense and on the photo it can be seen that the inside mold has been lifted some millimeters; this despite all the efforts to make the mold as strong and stiff as possible.
The weakest link turned out to be the wood on the top of the mold. Next time I will use more steel! (will there be a next time? Oh yes, I am already working on a LP-Terrazzo :-)
Already after some days the big moment was there. We cut open the molds with an angle grinder and revealed the result. The mold has leaked a bit, since I forgot to close it with silicon, so we had to cut away some terrazzo to make it completely free. It looked a bit raw but … No detectable cracks! Yes!
This turned out to be a big job. First off all the immense mass is not so easy to move and polishing a round surface is definitely 3 times more the effort of a flat one. We also found the first small flaws, the mold had expanded itself somehow in the middle and the front was not straight. This had to be corrected by polishing off more from the middle.
In total 12 polishing/filling steps were required to get a smooth shiny surface. The result is perfect!
Building it up
Before building it up, I needed to take all the styrodur out. This turned out to be another massive task. For this I made use of an old drilling machine and a Dremel with extension and a router drill.
The result after it was empty (and cleaned):
To build up the filters I made use of an old cutting board from a famous Swedish company.
All the connections are soldered on the back side, also the wires are threaded through the board so that the soldered connections cannot be harmed during installation. On top of that I used a lot of hot glue to be absolutely sure that the components do not move, rattle or shake. I also labeled all the cables, to avoid making mistakes when I build the filters in. Here is the result of the 'Cutting Edge' technology! To mount the filters I used M4 iron thread rods that I have pushed in the styrodur mold before.
For the inside interior I used 5mm felt instead of 5.5mm "soft fiber boards". Felt is more expensive, but was in my case much easier, since the "soft fiber boards" are normally installed just before closing the housing and they do also not bend inside the round housing.
And to fill up the box I used of course the usual polyfill. One role in the mid compartment, 3 others loosely rolled up and divided in the 3 sections of the bass compartment.
The filter for Mid/High is installed against the BR pipe and the filter for the Low installed on the inside front side.
The connectors were installed. For this I slid away all the plastic and heated up the connector with an additional soldering gun (15W). And used another soldering gun (45W) to solder the 2 wires. At one connector I made the mistake to use too much soldering... the result was that one of the threads got full with soldering and it took me an hour with a lot of swearing make it clean again so that the bolt would run over it!
The cables to the mid and high speaker are threaded through the holes where the mold rods had been before. All these holes were later closed by using hot glue. The wires were just soldered on the speakers, to protect the speakers I used aluminum foil.
The ER4 is equipped with a wire with connectors and I got advised not to cut off these connectors since the wires are very thin and difficult to strip off and connect. So I used the single pieces of a connector strip to connect the ER4 to wires that go to the filter. For mounting the drivers to the housing I used M4 and M5 bolts which were screwed into T-nuts in the inside.
Since it was hard to predict how much there would be grinded of during the polishing process, I could only start with the design for the decoration rings after I had mounted the drivers.
On the internet I found a small specialized company called GreatStar who makes all kinds of rings for products for photography and telescopes. I sent my drawing and after several weeks I got 6 great black alloyed aluminum rings back by post. It was done very professionally.
I simply glued the rings on the terrazzo with a transparent glue with no dissolver.
So was it worth the effort? Absolutely! I have now a pair of great looking and fantastic sounding pair of speakers in my livingroom!
This project has cost me a lot of time. Every little step took thinking work because correcting afterwards is not really possible. But it is all been part of the fun of building loudspeakers yourself. Making small steps and learning as you go! That is what this hobby is about!
And did I meet my requirements?
- Budget wise, not. I went over with approximately 600 Euro.
- I kept most of the 'messiness' out of the house, emptying the mold was mostly done in the terrazzo workshop. Cutting styrodur requires a very good ventilation! I guess the damps are toxic, I had the opportunity to do this outside or sitting in a full opened door opening. What could not be avoided is that I needed some grinding and also using the router on the styrodur caused some fine dust.
I avenged myself! Yes! :-)
High End Design & Sound
The speakers nicely blend in with the rest of the interior, do not dominate at all, they look impressive though. The speakers are not directly noticed by visitors. I love the design, the dimensions are well proportioned. The round thick rings fit very well with the shape and do finish it off. I stepped away from black spraying the drivers. The ETON's I got, did look different (membrane color) to the ones that see in the listening studio. I guess these newer versions all use the same material, the greenish color is actually making it better looking :-) What I could do better are the rings over the ER4. To my opinion they are too 'deep' now. I have not heard a difference though after I mounted them. Do they work now as little ER4 horns? It took some time before the drivers were played in well and I am not even going to try to describe the sound. I don't have that much of comparison. What I can say is that the speakers sound unforgiving and precise. If you put bad quality in it, the speakers will directly tell you. This is in contradiction to 'lower end' other speakers where the sound will be muffled into a standard sound. Improving the rest of the chain can become a bit addictive, but can be seen as hobby of course. I am thinking of building a nice tube amp with a matching terrazzo housing :-)
Do they sound better compared to the wooden ones I borrowed? Difficult. I think you need the 2 versions side by side to make a good judgment on this. What is noticeable though is that the speaker housing does simply not resonate at all! I have played them at extreme loud levels, have put my hand on several locations but could not detect vibrations. This tells me that the mid and low drivers must work with minimal loss. I do sometimes get the feeling that the sound is very pure and clinical, but I absolutely love it!
One could discuss that the BR opening now ends in the area where the connectors are placed and that this is not a fully free opening. The area of the connector opening is double the size of the BR opening and I have rounded the ends of the BR by making use of silicon on the mold. This makes the pipe slightly shorter and should compensate for the not 100% free opening, well, that is at least my theory.
On the photos can be seen that the speakers are placed too close to the wall, the current living room setup does not allow a better setup.. (WAF:-). When I pull them forwards, the sound quality improves a lot. Luckily for me, we move house soon and the living room will be much bigger! The moving company will love me..
I am driving the speakers with a Pioneer VSX-LX70. This AVR has a feature called MCACC that does a EQ room calibration. After some experimenting, I learned that running the system in the 'pure' mode (with no room compensation) does not sound that good at all and when I listen to my FLAC music I run them now in 2.1 Stereo. I also allow a Klipsch SW115 (couch shaker) to rumble along a bit. On the photos can also be seen that I have been creative with patching my own cables. These are 4 pairs of 1.5mm2. They mainly look good with the speakers.
I think I also managed well to combine my own capabilities with experienced partners. The specialized work to mix, fill and finish the terrazzo was done by a company that has done this for decades, the same counts for the very nice black alloyed aluminum rings!
Special thanks to Sebastian, Steffen and of course to the team from Intertechnik providing this loudspeaker magazine and community.
Jean Paul’s Duetta
Jean Paul’s Duetta
How it came about
Now that I have reached the age when many of life’s decisions have already been made, I wanted to fulfill my long-held dream of having a nice “hobby room.” The hobby in question is music, with a little home theater show every so often. The room itself was renovated with a good deal of work on my part – we removed a wall, redid the electrical wiring, and put in oak flooring. The project gradually took shape. A system made with Rotel components was put together, and I pulled my old boxes from more than 20 years ago out of the basement and connected them.
It was clear from the start that the old boxes would just be a temporary solution. Like all of these projects, there was an important hurdle to overcome: approval from my dear wife. Up to then, she had believed that the most beautiful boxes were the ones you couldn’t see. That’s why we have a subwoofer satellite system set up in our dining room. But in the new room meant for relaxing, I was playing in a different league. I started by making my way to the local hi-fi shop. Unfortunately I, and above all my wife, was not satisfied with the solutions on offer, or else the sound didn’t meet my expectations. I don’t want to talk about the specific boxes here; I’ll just say that there were a variety of units in the €2000 + X range.
Somewhat sobered, I sat there at home with a wobbly sound system. The next day, I stopped at a magazine kiosk and came across one for DIY boxes. Great, I thought, I’ll get this issue. Maybe I’ll find some inspiration. I devoured the magazine and was intrigued by the possibilities, high-end projects flying around in my head. After two months the next issue landed on my desk, with more great projects. Well, let’s see what the next one has to offer…
At the same time, of course, I started reading things online and found out that there was a real DIY scene. I also realized that I had far too little experience with the material to come up with a decent result, and I wasn’t going to gain any. I’m not an untalented craftsman, but I’m no engineer. By now a good year had passed. I had read a couple more magazines, poked around online (my wife asked me if I had finished reading the whole internet yet), and naturally I ended up at Loudspeakerbuilding.com.
I had an idea: on the one hand, I think it’s hard to build something you haven’t listened to before. Sound descriptions can be very subjective. On the other hand, I wonder how it can be that new “super-projects” are introduced every two months. If a project is good, there can’t always be new and better ones coming out. So after long deliberation, I decided to visit these people. If there are that many people who are happy with the Duetta, Minetta or a representative from the SB series, I might as well take a look for myself.
The drive was a quick one. I was a couple of minutes early, and I stood in front of the listening studio feeling a little disappointed. Somehow I had imagined the shop looking a little more glamorous. Another customer was waiting too, and he greeted me with some concern: “Hey, do you know if the master is coming in today?” The store wasn’t open for another five minutes, so no worries, I’m sure the “master” is coming. And he did come. We soon started chatting, and I liked Udo’s friendly attitude right away. First he asked about my requirements (room size, system, usage, etc.). Then we came to the usual suspects: Duetta, SB. We started feeding the loudspeakers with music. A little of Bach’s organ concerto, then “Child in Time,” “Deep Purple,” “Basin Street Blues” from jazz guitarist Phillip van Endert, and finally Johnny Cash arranged by Rick Rubin. What can I say? I felt at home with the Duetta right away. A clear sound, nothing exaggerated, love at first listen.
But how would I resolve the WAF issue? After all, the Duetta is not exactly a small box, more like an overgrown boulder. As I explained above, the most important thing for me is music in stereo, then the home theater experience. My plan was to start with the Center. If it met my tonal standards, I could start thinking about the main boxes. I also decided to hide the Center in a piece of furniture I built myself, in keeping with the request for invisible boxes. So the design of the Center didn’t need to be perfect, and it was also an ideal test for the larger Duetta stereo box project. I took home the components for the Center – the project had begun.
The Center, test run and lessons learned
What was it going to look like? I hadn’t decided on the final design yet. But I knew I didn’t want to deal with veneer, since that takes a bit of experience and because the Duetta would require large sheets of veneer. Besides, there is plenty of potential for frustration, which I wanted to avoid. So I decided to use multiplex and finish the surface accordingly. I wanted it to be obvious that it was wood, so high-gloss paint was out. The surface needed to have some visible wood grain and a tactile structure. When I held the chassis in my proud hands at home, it was clear that a light shade, white, would look great with our dominant floors.
Armed with the list of wood pieces, I went to my local hardware store. I ordered the baffle board from the appropriate online retailer to make things easier for me with the router. I was sure there would still be plenty of work left. The hardware store even cut the wood fairly precisely, although the material (21-mm birch multiplex) was somewhat poor quality. The wood itself had large gaps along the cut edges, along with pressed-in gravel and discolorations. I started by refining the surface using wood putty (glue mixed with sanding dust and sawdust). I took care of larger flaws by gluing in toothpicks. All in all not bad, but work that I would like to avoid with the larger Duettas.
Meanwhile the baffle board had arrived, so I had all the materials. I compared the baffle board with the other vertical pieces and used a router to even out any differences. The next step was SANDING. To make sure the surface was living-room ready, I found the following procedure to be useful: sand the material roughly, first with a #60 grain, then #80 and #120. Then apply the first layer of stain (Clou XXX). Use a rag to apply it to the wood and polish it until all of the streaks have disappeared. Now the wood needs to dry in your work room for five to ten hours, depending on the temperature. Then sand the surfaces again, this time with a #80 grain, then #120 and finally #240. Repeat the process until the wood fibers are no longer standing up. After each sanding step, work in another layer of stain; each step will require less stain. I also made an important discovery: buying cheap sandpaper is not worth it. Bad sandpaper can turn the surface of your wood red, for instance, while I don’t have that problem with a brand-name product.
The rest of the Center assembly is actually predictably easy: the reflex channels are attached to the baffle board and the whole thing is glued to the base plate; then come the sides and the rear wall, and finally the lid – done. Since my Center was going to be mounted low, almost on the floor, and after some consultation, I planned in two bars to serve as feet so that the ER4 could “see” the ear. Otherwise I basically followed the original assembly plan. The channels were glued onto the baffle board using Lamello pieces. As a test, I proudly set the chassis elements into the openings. Horror! The opening for the ER4 was rotated by 90°. I checked my drawing right away, and it was correct. I tried to make the opening a little bigger so that the ER4 would fit. Unfortunately there wasn’t enough material left to screw it in – nothing worked. The online wood retailer handled my complaint quickly and with no difficulties, and a few days later I had a new baffle board. And I had learned another lesson: you need to check the fit of the materials and the parts before you do the next steps of the project. Let me just expressly state here that I am extremely happy with the CNC router.
Now I attached the crossover to a little piece of scrap wood, screwed it onto the rear reinforcement, filled the middle chambers with insulation and glued on the lid. All of the glued parts are connected with Lamellos. Then I laid the insulation in the outer chambers and put in the chassis elements. For aesthetic reasons, I didn’t use the screws that came with it to screw in the chassis, but rather drive-in nuts with Allen screws – more on that later. In any case, my pride and joy now stood before me: the Center! I couldn’t wait to connect it to the system to see how they would get along. And they get along wonderfully: its precise sound outperforms all of the other boxes in the room! In 5-channel stereo mode, Johnny Cash (Mercy Seat) is suddenly singing right there in the room, not spread out diffusely. My wife was impressed: “It sounds better than anything else we’ve ever had in the house.” Now if I could just come up with a good design for the main loudspeakers, nothing would stand in the way of “Project Big Duetta.”
Stripes are slimming
The main loudspeakers had a couple of tasks: they needed to be one piece, since the two-piece design looks too much like student housing to me (nothing against students or their housing!). They needed to be mitered. And they needed to have something that would integrate them into our living space without competing with the floor. I came up with various attempts using SketchUp; I think I spent a good 20 hours experimenting. The Duetta thread by Matthias (DA) in this forum was also very helpful, and he gave me his SketchUp file and an Excel table full of formulas – thank you for those! Anyone who wants to build it can PM Matthias; he’ll answer as best he can, and he’s very willing to helpt.
Finally, I came up with the idea of building two different boxes: one would have piano keys on the side made of leftover materials from the flooring project, and the other would have six strings across the front. I told a cabinetmaker friend about my idea. His response: “That’s going to be complicated! When you cut grooves into multiplex, you always need to pay attention to the grain, or the material tends to crack! The strings go from top to bottom, and the keys from right to left. That means you have different grain directions, which will probably look awkward.” So it was either the strings or the keys. In the end I decided on the strings because I thought they made the silhouette look narrower. Then it was time for another visit to the store, where I picked up the components. As I mentioned earlier, I wanted to avoid the problems with the Center and the bad wood, so I had the whole box made by the CNC service once my construction had been approved. The delivery time was accurate, but it still took a good four weeks. Then three nice heavy packages arrived. One thing was clear right away: our basement (just under 10 m2) is too small for the assembly work, so I decided to use the garden shed. It’s not any bigger, but at least you don’t track any dust through the house (consider the WAF!). The baffle boards have six grooves cut into them, each five mm wide and five mm apart, centered.
Pieces of the oak floorboards will be inlaid into these grooves. That means the surface treatment has to happen first, because it would no longer be possible after adding the inlay. So, as I described above, first comes SANDING and staining. My tip: If you want to be able to enjoy your loudspeakers later, make sure you use hearing protection – and wear a dust mask during the sanding, because there’s going to be a lot of noise and plenty of fine dust. In addition, the oak floorboards needed to be trimmed to the right shape, so I cut the pieces into five-mm strips using a circular saw. At 20 mm, the floorboards were good and thick, so I also had to trim the depth of the thin strips.
I screwed the slats onto a small piece of wood and trimmed off another 8 mm with the handheld circular saw. My initial attempts with a trimming cutter were pitiful failures – the material splintered. Next I placed the oak pieces evenly into the grooves, carefully tapped them in a millimeter at a time, and glued them with Ponal joint glue.
Once a piece of oak cracked, which raised my blood pressure considerably. But I was able to take the piece out and save the baffle board, so all was well for the time being. I trimmed the projecting ends with a round Dremel saw tip, and sanded everything smooth with a sanding attachment.
I made the holes for the Allen screws for the ER4 and the Hex 7-360/ 37 for an M4 screw with a 3.2-mm groove cutter on the Dremel, because it is essential for the holes to be even. Then I inserted the drive-in nut from the other side. Rather than hammering it in, I “pulled” it into the wood with a screw and a washer. That way the drive-in nut is guided by the screw, and it sits straight in the baffle board when you’re finished. I used a similar process for the 11-581-50 Hex, although I used M5 screws; I “pre-drilled” the holes with the 3.2-mm groove cutter, then enlarged them with a conventional drill. In order to avoid potential leaks, I doubled the baffle board in the upper section from the opposite side, and used an MDF ring for the bass. I used a Forstner bit to drill corresponding niches for the places with the drive-in nuts, which I then sealed with hot glue. I attached the screws with PVC washers, as shown. They protect the chassis and add an extra seal.
In order to assemble the boxes themselves, I “rented” the dining room for two days. Once again I realized that my options were limited without the right equipment and the right space, especially as a layman. That made me all the more pleased with the results. I had a healthy respect for the process of gluing the boxes together. I started with a side piece and placed the rear wall and lid on it.
Then I attached the separator for the upper section, next the other side piece, and finally the baffle board. In order to make sure the box was air-tight, I attached the Lamellos with joint glue and glued the inside edges with PU glue so that there was an extra strip of glue exposed on the inside.
In any case, it all worked, even if it was very difficult. For the second box, I put the second side piece in last instead of the baffle board, which was much easier. I tightened the boxes with tension belts and blocks, and forced them into shape with screw clamps.
It probably would have been better and simpler to work with more screw clamps, but I only had two in the right size, and I’m no cabinetmaker. No matter, I still ended up with two beautiful boxes. I built the frequency crossover for bi-amping and then screwed it onto a reinforcement (I glued on two felt gliders first to avoid vibrations). Then I added the insulating wool and attached the chassis and the feet. I gave the lid a striped pattern with multiplex slats, and sanded it for a long time to create a mirror-smooth finish. As a finishing touch, I applied wax oil, after sanding the white-stained surfaces by hand one more time with #600 sandpaper. Udo had recommended some rubber feet, which I set into the base plate by a couple of mm so the box looks like it’s floating 2 mm above the floor.
And there it is
Naturally I could hardly wait to hear the Duetta in my own home. So I set it up, connected it and listened. The first disappointment came right away: the right-hand mid-range speaker wasn’t doing its duty. I quickly unscrewed it to take a look, but it wasn’t the wiring. I took out the bass again and checked the crossover. The problem was quickly solved: a soldered wire had come loose when I put in the insulation. I screwed everything back together and connected it – the mid-range speaker worked! Now it was time for a little patience: I hadn’t used bi-amping for the boxes in the first step, I just bridged the bases to them. But somehow I had expected more bass, and a rounder tone. A quick look online told me that some people had to switch the poles in the bass to get the right results. But I had checked the crossover several times, and even had it checked by a colleague who is an expert in the field (thanks, Bernd!). The polarity wasn’t the problem, though – the amplifier had set the lower frequency limit at 120 Hz, a value that doesn’t even really make sense for a subwoofer. So I corrected it to 40 Hz, and after two hours it was finally there, that Duetta feeling. First I listened to the same pieces I had heard in the listening session (Phillip van Endert and his jazz guitar, and the album “The Time We Spend,” are highly recommended for anyone who gets excited about jazz guitar.) Then I was sucked in further and further into the quicksand that comes from pride in the project and fascination with the sound, and I had a hard time breaking free: Pink Floyd “One of these days,” Cat Stevens “Father and Son,” Jaques Loussier “Toccata and Fuge,” Frank Sinatra “Fly me to the Moon,” Beatles “Girl,” Dave Brubeck “Take Five,” and so on. The hours pass quickly when you are enthusiastically rediscovering your music collection. Interestingly, this is the first box where I can hear the differences between an mp3 and a CD or LP. So we rediscovered our good old vinyl, and we are enjoying many relaxing hours with it. The Duetta really is the Queen of Blues.
Now all that remains is to say thank you: thank you for your support and tips – it’s a level of service above and beyond normal customer support. Thank you to Matthias (DA) from the forum. Thank you to my buddy Bernd for checking the frequency crossovers.
I’m sure that I will be building two more Duetta Tops as rear boxes in the foreseeable future, but first I’m going to build a sideboard to serve as a home for my hi-fi devices and the television.
Duetta from Marcus
Duetta a la Gregor – or what I call the “Duetta minimal”
A little less than a year ago, I had the pleasure of hearing Duettas for the first time at Matthias’ place in Darmstadt. After that, I realized that my previous boxes were more nice than good, and that DIY was a real alternative. After jumping in with the SB 15 for the bedroom (very cool sound – but too small for the living room), I really wanted to have/build some Duettas.
Like others before me, the size initially scared me off. But sitting on the famous Lautsprecherbau.de couch, I was eventually convinced that a smaller model wouldn’t really do it. The MiDU was too “bassy” for me, and I liked the SB 240, but not as much as the Duetta.
After some back-and-forth calculations, I eventually finished the assembly plan for the “Duetta Gregor.” The cabinet is in one piece. The bass capacity is 1 liter smaller, and the HMT cabinet is 11 liters smaller than the respective single-piece box. That would still be okay, because you can save on volume in the high-mid-range area with a single-piece cabinet. The exterior dimensions with 22-m MDF are HxWxD: 109.4 x 34.4 x 37.4 cm. That still worked for me.
As you can see from the boxes, there’s not much new on the assembly end. The box is square, practical and functional. The front panel was cut out using a CNC router. I didn’t trust myself to do the piecework with veneers. A professional took care of that, along with the matching base cabinett.
For those of you entering new crafting territory (the way I was…), here are the biggest mistakes I made. Maybe that will help keep someone else from repeating them:
1. Breaking-in time: Before I installed the chassis, I did let it play a little bit, but it took a long time before the Duetta was more or less broken in. That was the first thing – now they’re great, and I couldn’t imagine life without them. So just be patient at first (maybe I also needed to get used to the new clarity…).
2. When applying the oil (I used Osmo hard wax oil and was very happy with it), I put on the first coat with a roller. That wasn’t such a bad idea. But I didn’t clean off enough of the excess oil. Sanding and polishing off the oil residue wasn’t exactly fun.
3. For the second oiling step, I used a cloth. Unfortunately the light was bad and I didn’t apply it evenly enough – so those results weren’t very good either. So I had to sand and polish again.
4. Painting the front was a nightmare. The MDF absolutely needs to be sealed with paint or something similar (not just on the edges). Even clear varnish doesn’t work without a primer, and half a dozen coats didn’t fix the problem. And of course I couldn’t do it in a dust-free environment. Finally, my cabinetmaker did a proper paint job for me, and even he had some problems with it. We were both at the end of our ropes – thank you, Martin!!! :)
5. I attached the front with wooden dowels. The hardware store sold marking spikes that you could use. I only had four spikes, but I wanted to put in six dowels. Using them twice is all right, but it was off by a couple of micrometers. It all worked out, but next time I’ll hold the whole thing in place with a tension belt instead of with weights – then it will be even more solid (or else I’ll just buy two more spikes).
6. I had bought a new soldering iron – it took me a couple of failed attempts to remember that you need to treat the tip with solder first.
I’m not going to say much about the sound. They just sound great to me! Since I don’t have a “normal Duetta” to compare them with, I don’t know whether I lost anything due to the smaller volume in the HMT cabinet. But it definitely doesn’t feel that way.
A couple words of thanks before I finish:
Loudspeakerbuilding.com team, thank you very much for EVERYTHING! The listening session was super! I am infinitely pleased that I came to visit you and then decided on the Duetta! Thank you for your many supportive emails, about everything from the length of the bass channel to the spikes vs. rubber feet debate. :) Your service is one of a kind, and I’ve never experienced anything like it. And I’m sure this won’t be my last project (my home office is already waiting).
Martin, Tom – thank you for the veneering work (and for gluing together the box), and above all for painting the front. The look of the loudspeakers is all thanks to you!
Last but not least, Matthias (DA): Thank you for opening up the world of Duettas to me, and for proving to me that sophisticated loudspeakers and DIY are not mutually exclusive; in fact, they almost require one another.
Thank you to everyone who described their results and experiences here in the forum. It was an enormous help when I was doing my project!
The “only true” Duetta can only be purchased from Intertechnik.
Martins Duetta (Grandiosa)
Duetta – a dream of a loudspeaker
Martin fulfilled his desire for something special to play back his music, and he wrote us a wonderful report about his subjective sound impressions.
I’m an old hand at hi-fi equipment – today people would say “high-ender.” But since even that term is no longer what it used to be, I prefer to describe myself as an audiophile. What that means: because of my budget and my listening experience, I was always looking for the best possible way to reproduce recorded music. Sometimes more, sometimes less. In my youth, I was proud of my NAD 3020. That was then. Now I’ve ascended to heights that sometimes cause people to make an energetic twirling gesture with a finger next to their temple. But that’s how it is, my hobby. Once you’ve caught the bug…
Be that as it may, what I actually want to point out is that my evaluation is based on components that – in my opinion – are capable of reproducing even the subtlest details of the recorded sound… assuming that the sound engineers, recording and pressing technology allow it. Ultimately, the issue is not so much finding the better loudspeaker, choosing the perfect cable or answering the ever-present question of whether a record or a CD is the better reproduction medium. If the sound engineer botches the job, even the latest Blu-ray player won’t help, unfortunately. But let’s forget about that for now.
About my components:
I play CDs through an Audiomeca Mephisto II with a souped-up power supply and an external 128kBit DAC with selected components. I use an Octave HP500 SE as a pre-amplifier, and the corresponding Octave MRE130 monoblocks for the output. I run them on matching KT88 Gold Lion tubes (the tone is rounder, and they have a deeper bass than the original tubes). The MRE130s have Hoffmann SBBs (Super Black Boxes) for improved power reserves. Basically, each one is a separate box with a whole battery of capacitors. So it’s a potent power source for demanding sound converters, even though – something I should mention at this point – the Duettas are not the most demanding of sound converters. Especially with the impedance correction in the crossover.
The power supply for all the components comes from a power cord connected directly to the in-house distribution cabinet, with its own melting fuse. The wall socket is made by Furutech, and I use a PS-Audio Power Plant Premier for the power strip. It’s a fairly luxurious power distribution system, I admit. All of the cable connections, whether for the power supply or Interconnect, are from the Silent Wire Reference series.
So you can see I belong to the genre of “cable fetishists.” In addition, though, there are also several serious and less-serious measures for tuning devices and listening rooms that fully discredit me and mark me as a follower of voodoo and esoteric practices. In a sense, it’s the “coming out” of every high-ender (with thanks to Mr. Kirbach from the magazine STEREO). During my listening sessions… um, I mean my occult voodoo ceremonies… I use such obscure components as a disk demagnetizer, room resonators (singing bowls) and even a Schuhmann resonator, and I don’t shy away from beveling the edges of the CDs (*eek*). Just incidentally, that’s one of the most effective tuning measures, since it dramatically increases the three-dimensionality of the disks, and every recording fundamentally loses its digital hardness. It’s definitely NOT my imagination. I like to call it analogizing the recording. The only problem: it takes some effort to get used to the idea of putting the sickle to your beloved recording media.
For the sake of completeness, let me just mention that my listening room is also sound and listening-optimized through carefully placed acoustic foam mats. So anyway, without fanning the flames of the usual theological and intellectual debates that always flare up about these metaphysical-seeming tuning measures… you can see that I pursue my hobby with a great love of detail, and that I’m not afraid of obscure experiments. Because it’s a hobby. And it’s fun to experiment.
Let’s get to the real subject: the sound converters:
Until now, I used speakers called Reference 2 (manufacturer’s name removed by the editor). They’re excellent speakers if you primarily listen to pop and rock music. The sound is crystal-clear and crisp, they have a full, gnarly bass, and they never sound over-exerted at high volumes. The only annoyance might be a neighbor or your wife emphatically asking you to turn down the volume. In addition, Reference 2s are completely sufficient in terms of the electronics they use. I never had to move the volume knob past the 11 o’clock position.
As an old and/or former electrostatic speaker fan, what I especially liked about the References was how they illuminated the room in a wonderful three-dimensional way, untangling even the most complex musical happenings. The speakers never lose their overview, even for very large orchestras (e.g. the Clevelanders) in the loud sections of a forecful Tutti…
somehow I was never really satisfied with the sound of the speakers.
Well, because I’m NOT a pop and rock fan! That’s the main reason. I’m an out-and-out classical and jazz listener. So the quality requirements for my loudspeakers are different – I’m not looking for bone-dry basses and crystal-clear high notes even at ear-damaging volumes. In that sense, these top-rated high-priced converters were a classic purchasing mistake for me, and at the same time they clearly proved that there’s no ONE perfect speaker. Listening is a very subjective thing, and ultimately it is also closely tied to your own preferences. It doesn’t matter what the various testing magazines, with their point systems, might suggest as the top rating. It doesn’t matter how objective you think these trade journals are, or whether you think their opinions have all been “bought.” The fact is, listening and listening preferences are subjective through and through. Even for an editorial staff. Anyway, to cut a long story short: for a violin or a brass instrument, the Reference 2s sound(ed) too superficially clear (to me), with an excessive focus on the high notes. At first listen, they sound nearly perfect and overshadow everything around them. But in the long term, they were much too sharp for my ears, with exaggerated clarity. The longer I had them, the more I noticed it. Although it should be said that it might have had more to do with a lack of symbiosis between the acoustics in the listening room (concrete ceiling, wood floor, stone walls, sparse furnishings) and the speakers. In any case, it was time for something new…
During my extensive search for new speakers, I was actually just about ready to buy myself some heinously expensive pieces. We’re talking Avalon Eidolons or something in that category. But the exorbitant luxury price kept me from taking the leap. (Or was it possibly my wife??) Then a music fan and fellow sufferer told me to look up a speaker called the Duetta online. He said the reviews of the assembly kit were very positive.
Duetta? Do-it-yourself? Me? That’s crazy!
After all, I was looking for the ultimate sound converter. Not for some novelty speaker from the crafts corner. It reminded me strongly of my first serious experiments in the field of hi-fi. Back then, too, girded with a drill and a saw, I had installed mostly Scandinavian drivers into wood cabinets. It was fun, and much cheaper than buying the originals, which were much too expensive for my wallet at the time.
In any case, after extensively studying various entries in the online forums, I made initial email contact with Udo. I should say here that it was a very eye-opening contact. I quickly realized that this was NOT one of your typical “Commercial speakers are all overpriced and I can give you much better performance for much less money” spiels. No, our conversation was actually very serious and informative. It was easy just to indulge in a little shop talk with him and compare listening experiences. In any case, he not only shared/confirmed my own opinions about the Reference speakers, but provided me with a specialized technical explanation. That created a huge amount of trust.
Once I started playing around with the idea of building a cabinet for the Duetta assembly kit that looked anything but homemade, Udo gave me extensive help with the implementation and answered all of my countless questions at lightning speed. And – this should also be emphasized – I had not yet bought a single component from him at this point. It was really great.
here as a Zip-file.)
The cabinet itself – you can see the homage to the Avalon Acoustics loudspeakers – was made by a cabinetmaker with a CNC router. Before making any attempts to reconstruct this project, be warned: these cabinets are a curse! There is not a single right angle or parallel wall. Creating this cabinet probably cost my cabinetmaker several years of his precious life, and it is probably one of the main reasons that Avalon speakers are so expensive. It all has to do with the cabinets.
Anyway, now we come to the important part...
Was my (repeated) blind purchase worthwhile?
My sense of anticipation was predictably great. My first impression after assembling the chassis and crossover: it works. Sound comes out. Nothing is exploding, nothing sparking or smoking. But the sound that came out of the converters was less than satisfactory. Everything sounded very, very two-dimensional, fairly compressed, and even the highly praised tweeter sounded fairly papery to me. Okay, I thought, no big surprise – I just switched on the components, so this is like an initial startup. The system hasn’t warmed up yet, so you can’t expect it to sound good. But was the oft-cited potential really in there? As I said, listening is subjective. And of course it’s very dependent on the components and the acoustics in the listening room, and on your own listening habits. But setting aside the odd adjustment here or there, it wasn’t at all what I was used to. It sounded more like a cheap Chinese import than high-end equipment. Since it was already getting pretty late, I set the CD player on repeat and left the system running overnight. The next day I would have my first real listening test.
My furrowed brow wasn’t completely gone, but the second listening impression was already much better. The reproduction now offered a kind of spatial depth. It was still clearly behind the 2DC, but there was some development at least. It wasn’t a mashup of sounds anymore, but now there was a clear left-right differentiation and the instruments were easier to locate. A clear sign that the speakers needed time to warm up. Plenty of time, as Udo later confirmed for me. You needed to give the drivers 100 hours before they would play with complete freedom. I can absolutely second that, in retrospect. In any case, it was clear to me after the first listening session that I would need to play the Duettas constantly for a few days and nights. And that’s exactly what I did. So what was the final result after about two weeks of breaking them in? (Drumroll, building tension…) I now have exactly what I was looking for. A loudspeaker that not only looks great, but also sounds much better than anything I had in my listening room before. I have my dream loudspeaker! It might sound like an exaggeration, but it’s not. Would you like a longer explanation?
Okay, maybe this is the best way to describe it: the Duettas have a built-in ear-flattering feature. That doesn’t mean a diffuser that makes everything sound washed out, powdery and soft. No. The high notes are silky and clear, but without any trace of hardness. In particular, the snapping, clapping and hissing sounds come through very subtly and without any agitation. They lack the sharpness I’m used to hearing, and the messy hiss of a metal or woven calotte. In fact, I’ve never heard the “psst” sounds in the opening sequence of “El Canto de la Sibila II” (Auvidis 1996, Jordi Savall, Montserrat Figueras) come across as naturally and subtly as they do with the Eton ER 4. It’s an exceptional converter. Absolutely. Even unpleasantly brassy trumpets and trombones (same CD, track 21) are downright fun with the Duetta, and the voice of Montserrat Figueras is pleasantly assertive but never metallic, harsh or throaty. Representing a voice in a silky soft way without losing its intensity and especially its authenticity – that’s impressive. It’s as if she were standing right there behind the microphone, and the microphone is the only reductive technical link in the chain. The calibration with the 7-360/37 HEX – which is key in this interaction – seems perfect. So praise is also due to the mid-range speaker, not just the ER4. While Figueras has breath, a body and stature, a plucked lute has a clearly “visible” resonant body made of wood. And the plucked strings sound so soft that you are willing to testify they are made of natural gut. Overall, you don’t have the sense of listening to a sound recording. Instead, you are observing the performance behind the microphones. Everything has breath, a body and air, and above all plenty of space. The church is illuminated down to the smallest corner, and the missing room depth I mentioned earlier is completely gone. It is the same fantastic room depth that also distinguishes the Reference 2DC. In contrast to those speakers, however, the action is slightly more in the foreground. Not so far behind the speakers, in other words – closer to the listener. And – I think because the Reference basses are positioned on the sides – the image is reproduced more narrowly between the speakers. Whether one or the other is more “correct” can only be determined by a direct comparison of the live performance. But everything is wonderfully three-dimensional, and all of the sounding bodies are sharply focused within the room. A concert piano comes across more realistically than I would have believed possible in my chain of equipment. It felt like I could reach out and touch it. That is how it’s supposed to be.
Now for the bass of the Duettas… It isn’t as powerful as the one in the Reference. But it is deep and very precise, which is clear especially when you hear quickly struck kettledrums or bass drums. The Duetta is a little more reticent here than the 2DC, but that also means it is less aggressive and more pleasant. Not that there’s a shortage of bass. No way. But the sound waves don’t knock you over right away. They aren’t the kind of acoustic waves that give you a new blown-out hairdo. The focus is not on the effects, but on the music, which rightly has the greatest impact. Everything is just conspicuously inconspicuous. In a sense, the loudspeaker doesn’t even exist. You don’t have the feeling of hearing a loudspeaker. It isn’t there. And in reality, THAT is the goal of every audiophile. That is how it should be. The calibration is round, uncomplicated and harmonious. I think that’s exactly what Udo’s earlier “tinkering” with the Duetta crossover was meant to achieve. Whether it uses a film capacitor or an electrolytic capacitor, the result was/is what counts. Not the name. And from my perspective, the crossover is perfectly calibrated. The Duetta doesn’t reproduce sound, it plays. It has a clear overview and maintains it even in loud, powerful passages (Orff, Carmina Burana, Deutsche Grammophon 4D). In a choir with many voices, you can still clearly pick out the individual singers and their positions without having the sense that the Duetta is dissecting the music with a scalpel. The music is still part of a whole. There are no breaks. It is not glassy and transparent, nor wooden and stuffy. The loudspeaker and the musical performance simply have fusion, body and plasticity, as high-enders like to put it. The resolution is just as good as in the Reference 2DC, but it sounds much softer, more natural and smoother in my listening room and to my ears. I am more than just satisfied with my Duettas. I think – I hope (!) – that my speaker issues have been solved for the time being. Compliments to you, dear Udo. Even though I refused to listen to your recommendations/ instructions about the interior wiring and I used something higher-quality (in my opinion) than the simple copper strands after all. And thank you again for your valuable help and your nice email correspondence.
P.S.: I am still blown away by my listening session yesterday evening. The Duettas keep getting better. On that K2 sampler, track 8, Heart of Glass, that I like so much... to be honest, I never heard the recording sound so authentic and intense, almost private, on the Reference 2. And the piano finally sounds like a piano. It’s just awesome.
Best wishes from Switzerland,
A different kind of Duetta.
Hi-fi has fascinated me ever since I started earning my own money, which was a long time ago now. Back then, I bought myself a Sony system with dual boxes. It was an almost unaffordable hobby for me, and that was a good 27 years ago. I had just finished my training as a cabinetmaker, and unfortunately you don’t earn a whole lot in that line of work – not much to live on, but enough to survive. I still didn’t quite see the inherent virtue in craftsmanship. Health problems forced me to change professions, but my passion for hi-fi remained. Still, I had never thought about building speakers for myself. Now I work as a chemical sales engineer, a field where you meet all kinds of people – some of whom even share your hobbies. Most of the hi-fi freaks I know don’t really consider the option of building their own speakers, they find it a little ridiculous. Sure, if you spend at least €20,000 just for the loudspeakers, they must sound good. I don’t have that kind of money lying around, because I have a dog, nearly grown children, a wife and a house to pay off.
So you hop around from one high-end studio to the next, and go to all of the demonstrations and trade fairs in your area. Your ear becomes more and more well-trained, and the desire to have something great in your own home becomes stronger and stronger. Now, all of these listening tests didn’t end up giving me a new speaker system, because only my standards were growing – not my wallet. Maybe that was the point where I started to wonder if there were any alternatives, that is to say equivalent-quality alternatives at a smaller price. That led me to the internet, and naturally to do-it-yourself projects. And do-it-yourself leads you to Intertechnik. That was around Christmas last year.
As a sales guy, you naturally have some ideas about customer-oriented behavior. I was immensely impressed that my initial questions were answered so quickly and pleasantly on a holiday. The logical next step would have been to stop by the listening studio, but I didn’t do that. Just under 700 km, one way, isn’t pocket change. So first I read and absorbed all of the published do-it-yourself reports, which in my opinion added the flavor to the magazine soup. And of course I set my sights on the Duetta, the Queen of the Blues. Simply the Best!
It was an unusual decision. I was building a speaker I had never heard in a shape that had never existed. What encouraged me was that the shape of the boxes was very flexible as long as you followed the rules for the volume, baffle-board size and the reflex channel. So I started planning – what’s important, what can I change, what should I avoid? The Lautsprecherbau.de homepage (LoudSpeakerBuilding.com) was a big help, along with Udo and Intertechnik. In addition, I could have Udo (and of course my wife) sign off on the designs.
The first draft !
In all of the excitement, had I been abandoned by my otherwise very rational thinking? Where was I supposed to bring such an ambitious project to life? At the time I didn’t have a workshop – just a couple of amateur power tools and very few tools in general, but at least I had a garage. I bought a couple of used tools in online auctions. It’s still much cheaper than a pair of loudspeakers in this quality class. I thought to myself, if it works I’ll have both – a functional workshop and ingenious loudspeakers.
The time had come – I bought the MDF boards from a nearby specialty store. It came to almost 8 m² of 22-mm MDF. I got some PU glue to attach the boards – 4 kg of it. The main problem was finding a way to get back into woodworking after decades of abstinence. I was pretty worried about taking that first step.
First, I needed to make a template. I wanted to use the router to make sure the frames, the lid and the floor matched perfectly, so first I cut them out very carefully with the jigsaw and then smoothed them with sandpaper to make sure there were no grooves. Next I screwed them onto a 22-mm MDF board. “Now it’s going to be quick,” I thought, “I just need to run them through the router and I’m done.” The router I was using did fine with the 22-mm board, but it took incredible force. The router was holding onto the user more than the other way around. Two 20-liter buckets of MDF sawdust later, I was done. What really took a lot of time was the finishing. But if you want to avoid trouble with the gluing later on, you need to make sure that all of the shelves really match up. Then I cut the vertical frames, which gave me the distance between the top shelf and the bottom shelf. To glue them together, I wrapped the inside baffle board in a thin plastic bag that could be removed later. The inside baffle board gave me the angles and the exterior shape for gluing. I was able to put the vertical frames and the lid together to make a very sturdy cross. That’s what you might call the cabinet matrix. To the outside of this matrix (make sure it has a right angle) you attach the trimmed MDF slats, 3-4 cm wide, with screws and glue. That means pre-drilling the holes for every slat, moistening them, gluing and then screwing them on. This is where you can see the benefit of the PU glue. After 10-15 minutes (depending on the ambient temperature), it will start to swell. Moistening the wood before gluing it helps bind it, and it makes the glue swell up and set. This ingenious glue is a symbiosis of hardness, rigidity and elastic durability. It is also very filling, which is perfect especially for this construction technique. You can clearly see the individual slats in the picture.
Now it was time for the interior construction – whether it was necessary or not, I was obsessed now, and I wanted to make a good thing even better. So first I sanded the interior walls smooth.
After that, I laminated on a 4-mm layer of bitumen with slate. Because that wasn’t good enough, I also added a 5-mm layer of felt. I got it from a felt factory, one of my customers. They normally use it for the hammers on pianos, and with a little contact adhesive it sticks to the bitumen like magic.
Only then did I glue in the baffle board, having already cut out all of the openings for the chassis. That way if I made a mistake, it would just mean a little more scrap wood. If it had been glued in already – given how much work was involved – a mistake would have been very painful. Another advantage of this method is that you can fit the bass reflex tube into the inside baffle board and have it bump up against the outside wall. You can use a PVC drainpipe, but I used a sturdier plastic pipe with thicker walls. I glued it in with hot glue, which holds incredibly well. Just make sure the glue is really boiling hot! The coated pipe is then twisted into place.
The total length of the surface from the baffle board to the end of the tube is 420 mm. A square channel was out of the question because of the shape of the box. The opening at the front also makes it easy to set it up near a wall.
For the outer surface, I was less worried about neutralizing the baffle boards than creating a homogenous surface. Gluing a 3-mm fiberboard panel to a rounded surface is advanced stuff. Anyone who has ever tried it knows what I mean.
Before I forget to mention it, I also put together a bracket to separate the mid-range cabinet from the bass – here’s a picture.
I gave the speaker walls two threaded inserts to attach two M10 stainless-steel screws. The bearing in the loudspeaker bracket consists of a special composite pipe made of aluminum, PVC and polyethylene on the inside. MDF by itself would have worn down quickly in this type of mount, since the upper box alone weighs more than 20 kg. With this bracket, I can point the speaker right at where I’m sitting.
With the outer cladding, the bracket for the upper box and the beveled front edges, the boxes were finally ready to paint. If you want to make boxes this size, you should also get an upholstered pad like the one I used. I got it from a foam manufacturer and glued it together myself. That takes the anxiety out of setting the boxes down too hard.
Because I already have a lot of wood in my living room, I didn’t want to add another thing made of wood. That would have been too much. So I picked a subtle color – pearl white. One comment that many people have made: in a non-professional environment with non-professional tools, professional results are only possible up to a certain level.
What technology can’t accomplish needs to be done with sweat; in this case, that means endless sanding. It’s also a kind of fitness training – I lost 3 kilos and gained a good amount of strength – another positive side of making your own speakers.
The surface was sealed with acrylic paint. And if you’ll pardon my saying so, that meant a shi...pload of work. It was like an orange-peel effect!!! Use something else! Ask someone in a specialty paint store.
What did I do about it? I used #320, 400, 1000 and 2000 sandpaper for the entire surface – several times. Then the polishing. I also got a pro sander for a good price in an auction. Another comment here: if you’ve read my report up to this point, you know my work motto: “A lot helps a lot!” Well, okay – with paint it’s a little different. Even if you can believe the manufacturer’s claim that the paint is bone-dry in 2 hours and can be sanded after 8 hours, that doesn’t apply to polishing once you have added a few coats of paint. Let it dry for 2-3 weeks, then we’ll talk. What if you don’t have that kind of patience? In that case, the weather report calls for heavy clouds. Before your eyes start pouring rain, though – just be patient – the paint needs to be dry all the way down to its foundations first. Then it will really start to shine. I used a nanopolish to finish it. Used with care, it will work even on a flawed surface.
I would like to say that I’m at least a passable craftsman, for the most part. Even chemical reactions are a specialty. But electronics, soldering a crossover – that wasn’t easy for me. I managed it in the end, but I was amazed by how easy it is for some of the people here. I had to crochet the connection cord between the mid-range tweeter cabinet and the bass cabinet myself – I braided it out of 1.5-mm cable strands. There’s no real reason for it, I just wanted it to look a little nicer.
Here are a couple of pictures of the finished speakers:
I also set each of the Duettas on 3 high-quality rubber rollers. I absolutely recommend that, because they absorb vibrations very nicely.
Once I had positioned the crossovers and attached the threaded inserts for the M4 stainless-steel screws for the loudspeakers, I could hardly wait to connect the boxes.
The first listening test...! Huh?!!! What does my trained ear hear?! I admit, there was a great mid-range for starters – but where was the bass? I listened and listened, and didn’t hear it. After all, the Vincent SK 238 wasn’t exactly a weakling when it came to bass amplifiers. One more listen, with my ear right up against the bass membranes. Yes, something was happening there, but not enough for my taste. So I emailed Udo right away and voiced my distress. After first questioning my elaborately insulated loudspeaker walls, I had to take out the crossovers at least twice and check all of the conductors one at a time. I suspected that I had made some mistake in soldering or connecting them. Once everything was corrected and re-installed in the box, I just had to wait. The virginal chassis elements need time to settle in, too. So I let them play, and wow – not only was the bass much better, the mid-range and high range were improved, too. The bass I had been missing was there, and how. Where my old boxes had just rumbled, these had a precise presence that I can only describe as lifelike. I had recently been to a Nick Woodland concert, and now I put his CD into my CD player. Yes – exactly like that! I could hear him clearing his throat at the start of the first song, so real, and then the melody from his electric guitar – blues from the Queen of the Blues. I probably spent a solid two hours listening to everything you would normally play in a speaker test: Yello - the touch, which has an amazing bass line, women’s voices like Rebecca Pidgeon, the inacoustic CD Great Voices, and much more. What are the standards for a good box? For me, it needs to embody the music and make it feel like it’s live; it needs to take me to where the music was created and let me take part in the deep experience of the music. And now the Duetta does it better than all of the who-knows-how-expensive boxes I’ve heard in the past.
I was wondering whether I felt that way because I had built the boxes myself and put so much energy into them, so someone else needed to listen to them who would be totally honest with me. I took the opportunity to fire up the Duettas at a family party. I played the Great Voices for my brother-in-law, and I could see right away from his face that he was more than just impressed. Suddenly, the family party was no longer the main attraction. It got very quiet, and everyone just wanted to hear the music…!
It was absolutely worth it. And if anyone is wondering, the Duettas can easily take on any speaker in the “reference” class. Recently I was in a high-end studio in Ulm and listened to some boxes made by a very well-respected manufacturer, costing €30,000. What can I say, they’re good – very good, even, but the sound wasn’t any better than my Duettas. Sure, they were nicely made, but €30,000 – that’s what my VW Passat cost.
Be patient in planning and developing what you want, and also while you’re building them. It’s better to think through every step two times – if you manage to stay patient until the surface finish is done, you’ll have speakers that match up to the big names in the ready-made sector in every way. They’re just more personalized – and better, in my opinion!
Dear Loudspeakerbuilding team, thank you for all of your support and your fast, competent help.
If you want to build this assembly kit yourself too, you can order it from Intertechnik .
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