It’s not really that unusual for a loudspeaker builder to be given an unreleased product that will be used for the first time in a newly designed assembly kit. At least half of our assembly kits involve just these kinds of newcomers, from every possible manufacturer. There are plenty of them out there, constantly searching for new buyers by offering innovations, often without asking what the world actually needs. Our situation is much different with the Eton 26 HD 1, which has been tentatively announced for two years now – a new tweeter from Neu-Ulm that at first was only available as a sample to admire during the High-End trade fair. In the meantime, we didn’t hear anything about new miracles that it was performing, and we weren’t bombarded with measurements by some famous artist, like many Asian manufacturers, that usually turn out not to be worth the paper they’re drawn on once you take your own measurements. Series production was achieved completely under the radar, and the first set of new Eton tweeters was put into our hands as a special honor. And that led us to a real problem.
For many years, we have happily observed the uncommon virtue of the Eton managers, who avoid hectic movements and consistently follow their own paths instead of some rapidly vanishing fashionable trend. They have not put a new chassis on the market for a long time – why should they? They are still manufacturing a reasonable number of top-level products without any competition. New baskets, a parade of new membrane materials and voice-coil brackets aren’t necessary when the manufacturing quality is this good. So we were a little surprised when Philipp Vavron, the loudspeaker manufacturing company’s Technical Manager, suddenly presented more than ten new chassis elements at the High-End fair, featuring the familiar Hexacon membranes. Finally, he handed us the tweeter, commenting that it was basically finished but they were still working on it. And it did in fact take another six months before we had the completely finished piece in our hands. Since we’re not impatient people, we took our sweet time on the measurements and calmly spent the next three minutes in the basement putting together a 50-cm-square small baffle board with an inset for the chassis. We also had enough patience to put screws in at least two of the four screw holes to attach the 26 HD 1 to the measuring plate, and to connect the measurement cable. That’s how we spent our first ten minutes with this unique new product, without any idea that it could in good conscience be described as a treasure.
It takes some time getting used to the look of the 90-mm front plate diameter, but there is no fundamental problem with that dimension. The structure of the sound distributor, which consists of a cast plastic ring with four small supports, is also different from the normal mesh with glued-in film. Another unusual feature are the fat screws with washers that are used to hold the aluminum front onto its substructure. Basically, the tweeter has three parts. The membrane carrier is located between the front and the neodymium magnet with a large pole-piece hole, which is strongly rounded. Two different-sized openings on the right and left sides fit exactly over the two raised dots on the front. That forces the middle plate to be centered once it is screwed on, and the 25-mm voice coil is guaranteed to sit in the air gap without getting scratched. The membrane is a sandwich consisting of high-damping magnesium and an extremely stable synthetic ceramic that was applied to both sides using a plasma process. It is connected to the sound distributor and its aluminum voice-coil bracket through a plastic seal. The neodymium magnet is hidden in a flange-mounted volume with lots of ribbing and grooves. White cotton prevents reflections from the pole piece. Still, there is a small wave at 2 kHz in the impedance curve, in response to the large hole in the pole piece. Naturally we asked Eton if there was any way to avoid this optical weakness. Philipp Vavron’s response came by return mail: “Of course we used all of the means at our disposal to ‘combat’ that. We were able to eliminate it, but always at the expense of the acoustic quality. There were also side effects in terms of the rms value and fres. This ‘cosmetic’ defect can almost be overlooked for the average user, but for people who see sound instead of hearing it, it could be a real problem. All kidding aside, at the moment we’re not aware of any solution that would not have a negative impact on sound quality.” The Technical Manager’s response to our question about ferrofluid in the air gap was much shorter: “Nope!” came the clear answer.
Now of course the tweeter needs a partner that will take over the parts not covered in its name. Our first plan was to combine it with a five-inch speaker because that wasn’t in the inventory with ER4 yet. This was very energetically contradicted by the nearly 04 dB of sound pressure in the 26 HD 1 at 2.83 V. Two five-inch speakers would do better here, but it would work best with an additional bass. There is the BlueNote already, though, and we’ve even launched the version with the Seas NF 800 TV on the market. We solved the dilemma with two 7-360/37 Hexes, whose chassis description we can skip here. If you want to learn more about them, you can find the information in the Duetta and MiDu descriptions.
The chassis measurements were performed in a Kera 360.2 cabinet with a microphone at the height of the tweeter.
26 HD 1
Membrane: Magnesium ceramic
Voice coil: 25 mm on aluminum former
Magnetic shielding: no
Mounting holes: 4
Outside diameter: 90 mm
Milling depth: 6 mm
Installation depth: 26 mm
Fs 47. Hz
diameter 128 mm
Re 5.3 Ohm
Rms 1.73 kg/s
Cms 0.67 mm/N
Mms 17.0 grams
BL 8.14 Tm
VAS 15.5 Liter
dBSPL 88.1 dB
L 1kHz 1.12 mH
L 10kHz 0.42 mH
SD 129 cm²
MMD 16.2 grams
Z Min 6.0 ohm
Basket: die cast aluminum
Pole piece hole: yes
Centering:ventilated raised spider
Magnetic shielding: no
Voice coil: : 37 mm copper on aluminum former
Pole piece thickness: 8 mm
Linear excursiont: 7 mm
Magnet diameter: 102 mm
Mounting holes: 8
Outside diameter: 186 mm
Installation opening: 160 mm
Milling depth: 8 mm
Installation depth: 84 mm
Once the roughest work of putting the chassis together was finished, it was time to find the right home for the loudspeakers. The important thing was not so much the necessary volume, which we made nice and loud after a couple of LSPCad simulations by choosing 44 liters net and reflex-tuned, since we absolutely wanted to avoid adding a subwoofer. That’s already a lot for a compact design, even though the baffle board needed to be at least 50 cm tall because of the chassis sizes. No sooner said than done. To keep the box from seeming too misshapen, we made the front a practical 25 cm wide, which would have given us a good 50 cm of depth with the usual right-angled structure. So we drew a trapezoidal floor plan on our electronic sketchpad, with a 5-degree angle on the sides, and the cabinet design was done.
Well, of course that’s not strictly true – we then immediately had the idea to put a standing box with the same volume and baffle-board dimensions on paper, with the same narrowing angle to the back. It’s quite simple to put the boards together once you’ve sawn the front and back walls to size with the 5-degree angle. The process is quick if you use a circular table saw with a parallel stop; if you don’t feel like buying yourself this practical tool for building a single set of loudspeakers, you can also use a circular hand saw or a good old wood rasp. Still, the pieces will fit more precisely if you pay a cabinetmaker to do the cutting and maybe even the router work. It usually doesn’t cost much more than the hardware store plus brand-new tools.
Skipping the usual photo story at this point, let us try to find the right words to describe the assembly even without pictures. We draw the position of the first side wall onto the right-angled floor panel, and glue it in place with familiar old joint glue. Its emerging right angle comes from the rear wall, which is glued on next. To give the glue a little time to bind, we now put together the second set of cut boards, up to Board 3. Then come the fronts, the sides and finally the lids, alternating between the boxes. The glue dries completely overnight, and the projecting lid and floor panels can be cut flush with the trimming cutter. The rest of the smoothing work is done by the belt sander. Now it’s time to decide what the surface will look like. The veneer, adhesive film or newspaper will need to be applied before the cutouts are made. Painting comes afterward. If you don’t have a routing template yet, you should put one together using the assembly instructions in this magazine. You can always use it for other construction projects around the house.
As reinforcements, you can glue upright diagonal slats at random intervals around the inside walls. Soft fiberboard in the belly of the boxes is also more helpful than not. After your craft project, consider picking up a broom; all of that fine sanding debris and sawdust is likely to bother the lady of the house.
Cabinet drawing Kera 360.2 bookshelf as PDF-file
Cabinet drawing Kera 360.2 floorstanding as PDF-file
Once the accompaniment and cabinets had been found for the ceramic tweeters, it was time to add a couple of parts to make sure they only received the frequencies they could handle. Because the two bass mid-range speakers are happy to stand on either side of their new friend, they can also share the components for the crossover. The distance from the two chassis elements to the microphone, and thus to the listener’s ears if he is sitting in the right place, is identical even if the lower one is installed closer to the ground. The frequency curve of the 7-360/37 Hex installed in the box without a circuit (green) is, as always, the starting point for the development. A constant increase in volume can be seen here, from 200 to 1100 Hz, followed by a dip and then another bump at 4 kHz.
The rise is smoothed out by an air coil with 1.4 mm wire, although it does not manage to tame the bump (red
With the support of a smooth electrolytic capacitor, the type of capacitor that we thoughtfully prefer to use parallel to the bass or mid-range speaker, the volume drops with an even steepness after 1200 Hz, and the spikes at 8 and 10 kHz also disappear into the basement (blue).
The tweeter is a little louder than the two basses (purple). As a result, we connect a volume controller made of a fixed pre-resistor and parallel resistor (Mox, 5 watts) to its infeed and outfeed lines (green). To prevent too-deep frequencies, we then placed a 6 µF capacitor (or rather, two Audyn Cap Q4s, 3.3µF and 2.7µF connected in parallel), in the signal path (red).
Finally, we were able to magically create the desired decay in the lower flank using an air coil installed parallel to the tweeter but before the voltage divider.
The crossover branches intersect at almost exactly 2 kHz and are 6 dB below the total curve. We gladly accepted the slight waves due to the good addition in the transfer area; they are largely created by the measurement distance of one meter due to the baffle-board geometry
Since we still had almost 92 dB of mid-range volume left for the Kera 360.2 after the crossover, it would have been a shame not to make the impedance curve more linear. Even though people always say this is only essential for tube amps, we don’t know of any transistors that mind having smooth impedance behavior. As a result, impedance correction is as much a part of our standard delivery as the screws, interior wiring and Sonofil insulation.
You may have thought we wouldn’t notice: you just looked at the headline story, and now you’re already at the sound description. Did you by any chance skip over the pages in the middle? That’s okay, almost everyone does it – it’s not easy to tame your curiosity. We weren’t much better ourselves, but since we still had to put together a pair of boxes before we could hear it, our patience was put to a much harder test. What Eton had achieved with the new calotte was clear, but whether it could ascend to the realm of the ER4 with its somewhat unusual concept remained to be seen in the listening test. The listening test, like this introduction, was somewhat lengthy this time. With new loudspeakers, and not just as a developer, you are willing to be dazzled by a spectacular new way of presenting familiar sounds. More important than the quick listening test offered by the tweeter and the box was the long-term test, which reveals where you were misled by your initial euphoria. So we gave ourselves three weeks, listening to the Kera 360.2 again and again and comparing it to the ER4 boxes, presenting it to other people and getting to know all of its faults. It should be said in advance that we didn’t need to make any changes to the crossover – but to be honest, we had expected that.
Now we have finally come to the part that puts food on the table: no, we can’t say that the ER4 or the 26 HD 1 sounds better. The title “Setting out for new worlds” really says it all. The Airmotion transformer presents music in a completely non-showy way on a stage that is wide open in the back. All of the instruments are clearly defined, the musicians have plenty of space, and they aren’t fighting over a shortage of chairs. You can practically watch each individual musician play, with no effort on the listener’s part. Sounds from fingers gliding across the instrument and from the matching bows and sticks are reproduced just as they were created. Voices have a natural sound, as if they hadn’t made the long journey through the microphone and the sound engineer’s electronic desk. This unit manages to perfectly present the musical happenings from the boxes like no other.
The ceramic tweeter does exactly the same thing, except that it moves the stage three meters closer to the listener without losing any of the depth. Still, the listener never has the feeling that the boxes are too close. Naturally there are some differences. Where the ER4 tends to flatter the ears like a lover, the 26 HD 1 analyzes things with a little more hardness; but it never becomes annoying, which could unfortunately be said of many other hard calottes.
What was hard for us to believe was the self-confidence with which the Kera 360.2, the tweeter with its new composite material, presented every kind of music. We had previously only seen that effect from the corrugated bellows (ER4). In the last three weeks, we have learned that it is in fact possible to present all of the upper notes a little bit differently without having them sound wrong to our ER4-conditioned ears. A different world than fans of the metal chassis might prefer, to be sure, but without any sharpness.
Overall, though, the most amazing experience came to us somewhat involuntarily and certainly not on purpose from a woman who walked into the shop during a listening session, where we were playing Pink Floyd’s “Wish You Were Here” at an appropriately high volume. She had gotten a new cell phone, and she was telling us about all the features it had that nobody really needed. After a couple of minutes, we asked her if she recognized the music. She listened for a second and said, “Sure, Pink Floyd,” then kept talking with us about her work day. The music was truly loud, and the woman had not asked us to turn down that racket, which is what normally happens when the radio runs through the standard boxes. When we mentioned it to her, she said she hadn’t even registered the music as being loud. That was probably the best compliment that a sworn witness could have given the Kera.
Technology Kera 360.2
Chassis: 2 x 7-360/32 Hex
26 HD 1
Manufacture: Eton, Germany
Sales and construction: Intertechnik
Function principle: bass reflex
Nominal impedance: 4 Ohm
Connection terminal: K30-AU
Damping: 3 bags Sonofil
Reflex tube: HP 100 uncut
Wood list in 21 mm multiplex:
115,8 x 27,0 (4x) sides
115,8 x 22,0 (2x) front
115,8 x 14,0 (2x) back wall
27,0 x 27,9 (4x) lid/floor
Wood list in 22 mm MDF
with 2 mm glue added:
50,0 x 42,0 (4x) sides
50,0 x 22,0 (2x) front
50,0 x 29,0 (2x) back wall 32,2 x 41,6 (4x) lid/floor
The baffle board, back wall and sides need to be cut to size with a 5° angle.
7-360: 7 mm depth
26HD1: 5 mm depth
The bevels on the lid and floor can be made using a router, a circular hand saw or a power planer.
Approx cost per box: 550 Euro
The loudspeaker assembling kit Kera 360.2 includes all parts but not the cabinet.
The complete kit can be ordered at Intertechnik