Dirk’s Duetta Top
I had actually wanted to build myself a couple of “small” rear speakers, and I decided on the Duetta Top. But where would I put them, since there’s nothing tall in the corner and I didn’t really like the feet they come with? … I thought about it some more and did some calculations until finally the drawings looked right. I decided on a mounting-frame construction – I don’t think anything else would have worked for this shape. The first step was making the router template.
I cut it out of 8-mm-thick plywood (it looks hard, but you really don’t need anything other than a homemade routing compass). First I cut out the rounded parts and then the straight edges, choosing a routing width that would let me use the remaining piece as a “support” for the routing process – a little thicker than the smallest guide bushing on the router. That way the router doesn’t wobble later on when you’re cutting out the box pieces. The inside routing is similar, also with supports.
This is what the whole thing looks like when you’re finished (I cut out the inside part with a jigsaw later).
At the top, you can see the two supports that I left in place, partly for screwing on the router template and partly to increase the stability of the box for the 3 individual parts. All right, now comes the really labor-intensive part: 3 pieces without a cutout in the middle (2 front panels and 1 floor), 3 pieces with supports, and 10 pieces without supports. You’re going to need a vacuum – it makes a fair amount of sawdust!
Then it was time to cut out the front panel. That wasn’t so hard – a routing compass and a variable square template, and you’re done. Speaking of the front panel: make sure you only screw the template in at the spots where you will be putting holes for the loudspeakers later – in other words, only attach the top and bottom parts with a clamp, otherwise you’ll end up with ugly holes! Once you’re finished, it will look like this.
Now you’re ready for the gluing phase. I always glued two boards together at a time, then glued those to the next two, etc. I also made a vertical channel for the wires in one of the rear pieces. That way the wires don’t just hang down from the top – it looks better! Since a biwiring terminal was provided, I placed 2 wires at the bottom in case I wanted to take advantage of that option later on.
Since all of the pieces need time to dry once they are glued together, go ahead and put together the crossover now and attach it to the rear-wall support. Make sure that the base plate – for unpleasant eventualities – is not any bigger than the cutout for the loudspeaker (I hope I never need it!).
Put in the insulation before you install the baffle board!
Once the “shell” was more or less done, I cut out an opening for the terminal in the base. It’s a little unusual, but since I was also going to be attaching small feet to the bottom, I thought it was an elegant, subtle solution – there wouldn’t have been anywhere else to put the relatively large terminal.
And now comes the least fun part of the whole project – sanding! The straight edges and the round parts that I could reach with a sander were not a big problem, but the interior curves were hard. You need the right size pipe (the other end of the reflex tube was perfect), a huge pile of sandpaper, plenty of muscle power and a whole lot of time! I started with #40 grit – which was a big mistake! It took me forever to smooth out the grooves with #80. The next step was #120 and #180, and I finished with #240. I must have wiped and re-sanded the sides at least 6 times before I was satisfied. Then I stained the front and back walls white, and finally waxed the whole thing with antique wax, making sure it was nice and thick on the sides and then polishing it. It’s super easy, and the wax fills in any defects in the multiplex.
Here’s how the whole thing looks during the initial trial run.
In the middle you can see the main reason it took me a while to write this report and to finish the project (there were a couple of other projects, too – building a dollhouse, etc.). It still looks a little “crowded” and it’s not perfectly spaced, but that will change once the living room has been expanded and I can put everything where it belongs. In terms of the sound, I can simply add my voice to all of the builders and listeners who came before me. Now that it is broken in, I almost exclusively use the Duetta Top. In a blind test with my homemade Temperance and a purchased Sl590DC, several family members clearly preferred the Duetta Top, which really says it all. It has an amazing bass (ok, I have the sub for listening to organ music and various electronic blasts), and the “legendary” Eton ER4 is unbeatable. In particular, I think classical music and vocals are the main strengths of the Duetta Top. Christmas is coming soon, and the old trial amp standing on the sub will be replaced by a tube amp if all goes well. I think that will give me another good bump in quality.
Finally, I want to give a big thanks to everyone here in the forum for their fast, helpful answers, and an extra THANK YOU to the team at Lautsprecherbau.de. They could not have been any faster or more skillful at answering questions, and this definitely won’t be my last box. Thanks, too, for sending me the crossover circuit diagram so quickly.