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 .