Life as a loudspeaker builder and seller is very multifaceted. Putting together packages, building test boxes, developing crossovers and the fifteen hours a week demonstrating assembly kits are the easy part. My parents would never have believed how many people would come to regard the couch in our listening studio – which they passed on to me more than 15 years ago when it was no longer good enough for their living room – as an object of cultish devotion. Do-it-yourselfers love to sit on it and listen to the sounds of our proposed construction projects. That means whenever I need to write these kinds of texts, it’s hard to find the time for them, so this part of my job always suffers from terrible (time) pressure. But I’m not complaining, because I’m happy to pay the price. As a result, the update for the MiDu has been finished for a long time and I’m just now getting around to writing the report – some enforced breaks are on the schedule.
When Eton told us two months ago that one of our favorite eight-inchers could no longer be manufactured, the news hit us hard. Overnight, the Minuetta, MiDu and even the test speaker peacefully slumbering in my desk drawer were no longer available. We could have predicted that this day would come – it had already happened with the 7-360 and the 5-880, which were by far our most important basic chassis elements. In order to keep using them in our assembly kits, we are now having them manufactured exclusively for us, in quantities that suit both parties. It wasn’t a hard decision. That would have been possible with the 8-800 too, but it was much easier to replace than the bass mid-range speakers. Even if it wasn’t advertised as such, the BlueNote can legitimately be called the successor to the Minuetta, since the speaker construction is almost identical to the Symphony 285. More important than both of those is the MiDu, which quickly established itself on the market as a powerful but less-deep counterpart to the Duetta after it was released five years ago. Getting one was almost a sacred duty, as the forum’s reader responses to the discontinuation announcement showed. I had to give up something in the process – my unease about mixing the old and new Eton series. In keeping with the eternal phrase, “Nothing is forever!” I had waved off all suggestions along those lines. But after the 7-360 was continued, and given the justified hope that the irreplaceable ER4 would last a long time, my fears were eased. The only consistent thing was my choice of the name for the update: MiDu2. The most revolutionary thing about it was leaving out the space between the letter and the number.
After this long preface, I can now get right to the point: all we needed were some matching basses. The list of candidates wasn’t long – the only choices were the 8-200/A8/37 Hex with an aluminum bracket and the 8/202/C8/ 37 Hex with a cap sound carrier. Since there was no difference in terms of the required frequency range, we could even have installed a combination of the two. We decided against that; against our better entrepreneurial judgment, we chose the 8/202, more than 2 euros cheaper, which also differs from the dearly departed 8-800 only in terms of basket size. It requires a cutout of 223 mm, 224 mm on the outside and 196 mm on the inside with a coat of paint, and it fits into the same cabinet without changing the reflex tuning. That takes us right to the middle of the action: at right is the modified construction plan, but not as a SketchUp file this time. Making one would probably have delayed this report by several weeks, but do-it-yourselfers are welcome to send us their drawings. We will provide them as downloads here, and then everything will be fine. One small comment about the air volume of the 7-360: for the closed model, it only needs 12 liters; the roughly 20 liters of the Duetta Top are due to its reflex tuning, which can serve as a basis for the Queen but also for the MiDu(2) and Doppel 7 if it doesn’t want to spend a lifetime knocking around the living room by itself.
We aren’t really the kind of magazine that debates theoretical issues. We are much more interested in the practical work involved in helping people build things by themselves. As a result, we used the new CNC router to machine a couple of boards. We tried out a couple of things that make it easier to glue the boards together, and we threw out a couple of other suggestions, although they are still shown here. A significant factor for precise routing is the precision involved in placing the first three boards. Systems like joint mitering don’t forgive any errors here, so we had to be more tolerant. We were helped out by the grooves for the interior reinforcements, which are also responsible for the right angles. That allowed us to skip the edge guide later on, and to saw just one more mitered edge. We didn’t know that yet when the MiDu2 was built, but it’s not especially important for the assembly report.
The side wall, with its 5-mm indentations for the interior boards, is lying on the workbench, which has been covered with a pretty piece of paper. We start the assembly with the back wall of the mid-range tweeter chamber. Glue goes in the groove, board on top, glue applied for the lower board in the chamber.
An edge guide shows us the right angle and a yardstick measures the overhang where the groove and the front piece will come together later. The process continues in the same way with the other interior boards.
After the lid, it’s time to position the cover for the tweeter. Since the baffle board is made of 19-mm solid-colored MDF, a 3-mm indentation was made with the router to give the ER4 its 22 mm of chamber depth.
Skimping on glue won’t make you rich, but it will endanger the stability of your cabinet. Joint glue costs about 12 euros a liter, which is enough to make ten large boxes, assuming that your wife doesn’t also need a new shoe rack. Then you just have to reduce the number of boxes accordingly.
Once everything is dry, after about an hour, the back wall can be glued on. The front panel concludes the gluing work. All of the grooves are slightly wider than the reinforcements. That gives us a little playing room to set up the last board in the right place. Any glue that escapes will need to be removed by hand or with a sander later on. As we know from the wedding box project, Mathias (DA) now has a basement room where sanding dust doesn’t get into the shower anymore. Once the boxes and the paper cover are removed, the kitchen table is soon free for normal use again.
Anyone who likes the boxes to be painted or veneered all the way around should have thought of that before gluing on the back and front panels. After that point, only oil, wax or clear varnish make sense. Many readers’ boxes have convincingly shown that this also provides a respectable surface. A nice suit wasn’t really necessary for my work – how it sounded when it was facing the furniture was more important to me. So I started working on the crossover without having to wait for any paint to dry. First, I stuffed a bag of Sonofil into the chamber of the mid-range tweeter and six loosely rolled bags into the bass section. I had a good model from the circuit of the defunct MiDu; the mid-range tweeter unit was identical, and it was installed in the same environment. Just to see how the new basses – very familiar to me from the Symphony 285 – responded to the old network design, I put the corresponding parts in front of the only new components in the construction plan as a test. Naturally they didn’t have to put on a solo performance during the measurement – as we know, the crossovers handle the interactions. There were a couple of small complaints, so I went to my components shelf and picked out a couple of different sizes. In the end, they affected more than just the connection to the basses. The main structure stayed the same, with a 12 dB filter for the basses, 6 dB with a suction circuit at a weak resonance of just under 4 kHz for the mid-range speaker, and another 12 dB for the tweeter, which was also made a little quieter using a small resistor. The result was a frequency curve that would make a pure theorist’s hair stand on end when measuring the axis, but it bears my signature smooth curve as the angle increases. No impedance correction was needed for tube users, since the maximum fluctuation between 5 and 8 ohms doesn’t need to be smoothed out.
A look at the measurements concludes our creation story for the MiDu2.
Measurment diagrams, MiDu2:
|Frequency response and phase||
|Frequency response under 0/ 30/ 60°|
|Distortion for 90 dB||Step response||Waterfall|
In contrast to my usual approach, this time I built the crossovers on circuit boards. It makes sense if you know that this assembly kit will soon come with ready-made crossovers from Intertechnik. A provided pattern will make it easier to put them together, and the pattern doesn’t care whether the crossover was made by me or by Frank Schumacher. Since I need to install a couple of crossovers anyway, I can also glue them right onto Pertinax boards and solder them from the back. That also guarantees that the boards can be easily screwed onto the back wall through the bass cutout, in their permanent position just under the lower bass.
The bass part is assembled on an chess style printed circuit board, and the mid-range tweeter is partly assembled on a pre-drilled board without any brazing solder because their counterparts weren’t available in the right size. That shouldn’t be considered a defect, though – as long as no electrified circuit paths are running under the coils, I couldn’t care less how the back side looks..
Now we come to the part I can’t avoid, but that actually gives you the least information about the sound performance of the speakers: the sound review. The listening tests in our studio show again and again how subjective this is. Amazed glances, followed by grins, tell me a lot about visitors’ expectations, which were usually much lower than the sound on offer. Since MiDu and its successor do not have a very different sound – nor was that the goal – I could just copy Tom’s sound description from here. It still holds true: “The bass was dry, contoured and transparent. The bass player’s runs were easy to follow, and the tuba and bass drum didn’t sink into an undefined swamp of sounds. The spatial reproduction showed a stage that very credibly represented the recording site in terms of its width and depth. The hi-hat beats clearly showed whether the disc was being struck in the middle, on the edge or not at all. The singers had plenty of space and were a realistic size, and the drummer didn’t squeeze past them into the foreground. Small noises from musicians reaching for an instrument and from the audience were immediately perceptible. The brain didn’t have to analyze them to determine their cause.” But how can you tell from these mere words how the boxes actually reproduce music? I could write that sound description under every report from now on, because it is as true as it is vague when it comes to my construction projects. Still, an entirely emotionless description, no matter how true it may be in the end, is also not what the reader wants to see. Readers want to feel the pleasure that the listener experienced from the music and the boxes – the power of suggestion. Now, I had that pleasure recently when troops of musicians once again paid a visit to my listening room. A phone call with a random visitor summed it up: “You were listening to a Stevie Ray Vaughn record when I came in. Which live album was that?” “I don’t have any of his live albums.” “No, I’m sure you do, we listened to it together!” “Did you hear any applause?” “Now that you mention it, I can’t remember, but I’m sure it was live. Stevie and his musicians were standing about a meter behind the line of boxes and playing ‘Tin Pan Alley’ just for us. I’ve never heard anything that sounded more live!” What else can I say?
|Chassis||2 x Eton 8-202/C8/37 Hex||Wood list in 22 mm (0,866") MDF per piece:|
|1 x 7-360/37 Hex|
|1 x ER4||
120,2 x 42,0 (4x) sides (4,73"x1,65")
|24,0 x 42,0 (4x) lid/floor (0,95"x1,65")|
|Sales||Intertechnik||24,0 x 115,6 (2x) back wall (0,95"x4,55")|
24,0 x 112,6 (2x) front (0,95"x4,43")
|24,0 x 37,0 (2x) back wall, mid range chamber (0,95"x1,46")|
|Principle||Bass reflex||24,0 x 14,2 (2x) floor, mid range chamber (0,95"x0,56")|
|Nominal impedance||4 Ohm||24,0 x 17,5 (2x) cover for ER4 (0,95"x0,96")|
|24,0 x 18,8 (2x) reflex chanel (0,95"x0,74")|
|Damping:||7 bags Sonofil||24,0 x 10,0 (8x) reinforcements (0,95"x0,39")|
|Terminal||2 x K 30 AU|
|Approx. cost per Box:||Bass: 6 mm 0,236"|
|Kit without wood||860 EUR 900 USD||Mid range: 7 mm 0,275"|
|Wood cut:||50 Euro 55 USD||Tweeter: 3 mm 0,118"|
Die MiDu2 is available from Intertechnik. Free shipping.