Kerpen, we have a problem... That was more or less the response when we (Andreas Wolf, Udo Wohlgemuth and Patrick Even) sat down and talked about assembly-kit plans for the Christmas season a while back. We had some wonderful bass mid-range speakers called the Gradient Axis that we wanted to use, but we were still missing the right tweeter for the series. Patrick had long ago started to develop them, but they weren’t available for mass production yet. We spent a long time thinking about whether a model from the ferrofluid-free Seas fleet could spring to our rescue, but it wouldn’t have been fair to use the Norwegians only as tweeter suppliers given their own range of outstanding bass mid-range speakers. We had already used the Scandinavian tweeters in the FT 8 as well as the Elip 1 and 2, but we needed to combine manufacturers here, both for the sake of good sound and because of the lack of suitable tweeters for the transparent GDS 182. One way to escape this dilemma was with the first “Blub” – we could have put another four to seven assembly suggestions in the magazine with this model. After the first two, though, our readers would have been understandably bored: “Look, they built a ‘Blub’!” would just have been met by hefty yawns the third time around. The solution to our problem came somewhat unexpectedly when Fountek happened to ask Intertechnik if we could imagine working in Kerpen with this manufacturer, known for its excellent ribbon tweeters. Its chassis elements were even available in various shops, and sometimes featured in construction magazines, but there were no active sales. We could imagine it very well, in fact, because for one thing we hadn’t had those types of drivers in the product range before; for another, they fit very well with the Axis series in terms of appearance. That’s how we came up with the first assembly plan, which we dubbed the Axis 34 Neo for simplicity’s sake.
No other frequency range has as many model types as the tweeter. Today, the standard model is the calotte, whose membranes made of textile, metal or plastic are set in motion using a voice coil suspended in a magnet system. The carrier and wire increase the driven mass. Fundamentally, the calottes are a further development of the venerable cone, whose technology was mainly adopted. Foil tweeters differ from these in a fundamental way because they do not use a separate voice coil. This is replaced by conductors that are vapor-deposited directly onto the membrane (magnetostats, air motion transformers) or even by the foil itself (ribbon). A hair-thin aluminum strip is the material for the oscillating unit; in contrast to the other models, it generates an electrical drive and mechanical sound transformation using just one component. However, its resistance is in the low milliohm range.Therefore an additional transmitter needs to be installed between the amplifier and the membrane that can correspondingly convert the load upward and thus provide the amp with the appropriate 4 to 8 ohms. We can find it in the box attached to the rear of the ribbon tweeter, which correspondingly requires a sufficient installation depth. Naturally, this kind of signal conversion affects the price; much more raw material is needed than for a small voice coil. It buys us a much lower membrane weight, which allows even the smallest stimuli to be heard and produces a significantly finer resolution. It is obvious that the previous sellers of the Fountek chassis tacked on a substantial additional price for this exclusivity. How else can you explain the fact that Intertechnik was able to reduce its price for the end consumer.
Our first contact with Fountek ribbons was several years ago; at that time, we cobbled together an assembly kit with the NeoCD 3.0, which we liked very much because of how it played. It also made sense for the Axis 34 Neo, but we were more curious about the driver with a short horn attachment, called the NeoCD3.5H, which is more directional at high frequencies and at an increasing angle. That was just right for us, in combination with two AXT 06 models bookmarking the tweeter. We published its details and measurement diagrams here , and reported on its die-cast basket without any additional ventilation as well as its outstanding series consistency. That’s why we are only giving you the bare measurement data for the NeoCD 3.5 H here.
NeoCD 3.5 H
Item No.: 1420056
Measurements as Zip-file
|Membrane:||Aluminium foil||Magnetig shielding:||no|
|Voice coil:||none||Pole piece hole:||no|
|Winding height:||none||Mounting holes:||4|
|Pole piece thickness:||none||Outer diameter:||98 x 104 mm|
|Linearer excursion:||----||Installation opening:||70 x 90 mm|
|Membrane surface:||7 mm²||Installation depth||101 mm|
|Magnet:||Neodym||Milling depth:||3 mm|
Parameters cannot be given for the ribbon model because it represents nearly pure ohm resistance without any recognizable resonance..
|Frequency response and phase||Impedance||Frequency response under 0/ 30/ 60°|
|Distortion for 90 dB||Step response||Waterfall|
It was not really surprising that LspCAD’s calculation for two AXT 06 units only produced a volume of 16 liters with a reflex balance of 55 Hz. The rough estimate of the parameters had also suggested a fairly small cabinet. However, that gave us plenty of reserves for a slightly larger cabinet; a compact box had been planned, but with a baffle-board height of at least 50 cm and a width of 19 cm, the result would have been a misshapen little box with just 20 cm of exterior depth. We much preferred a volume of roughly 25 liters, for which we expected deeper tuning at 16 cm of pipe length and thus a gentle decline below 250 Hz to nearly 40 Hz. That also gave the cabinet for the Axis 34 Neo an aesthetically pleasing exterior with a depth of 30 cm. Still, the NeoCD 3.5 H was unappreciative of our choice to cut out the outer design, which requires at least three years of experience in cutting CNC to size. Still, we knew what to do – a 3-mm corkboard was our friend. The assembly is not complicated, but still worth a few pictures because of the special nature of the baffle board.
Since some of our readers have trouble finding the captions, which only appear when you click on the image, today we will write everything in a continuous flow in the hope that our readers won’t end up doing the same. We also promise to keep it short. We will use a semicolon to separate the instructions.
Black pile of boards with corkboard; board on the cork, cut to size with a box cutter along the front panel; no words; roll wood glue onto the front; place front on the corkboard and align; press together and let sit; joint glue on the cut edges of the lid; glue is distributed after a little wiggling back and forth; put the lid on; align it; glue in back wall; and front wall in the same way; guide board shows the placement of the floor; and the reflex board; glue on all of the projecting cut edges; align second side; two finished cabinets.
Now there are always questions about how to make the boxes look nice and the cutouts clean. We’ll illustrate that with a few photos too, this time with captions.
The router template consists of two 50-cm-long aluminum profiles that can also be used as curtain rails. Using simple hardware-store fittings and a little fiberboard, you can put together a handy tool that keeps the router from wobbling but allows it to rotate freely. The 30-mm-wide hole just fits the copy ring, which touches the left side when the compass moves in a clockwise direction. The slider on the right side, with a 5-mm screw as the fixed point, provides the correct radius. In order to set it precisely, we screwed a piece of a ruler onto the bottom, just under the end of the wooden slider. The number under it shows the exact radius if the measuring tape has been adjusted correctly. #10 and #20 compasses need to be set differently, of course. Cutting, measuring, aligning and cutting again is helpful; if necessary, you can repeat the procedure if the dimensions are off.
After the cutouts, the countersinks for the tweeters need to be cut out of the 3-mm cork. That went just fine without any words, but it did take fixing screws, a box cutter and chisel. After that, all of the chassis elements fit into their cutouts, flush and without any wobbling. In order to replicate this artwork, the do-it-yourselfer just needs the assembly plan, which once again can be downloaded as a SketchUp file. But in order to fill up the page nicely, here are two paper drawings anyway.
In order for a loudspeaker choir to know who will do what, it needs a director. In trade jargon, this is known as a crossover. In order to find the right parts, a box was placed on the measurement stand and the microphone was pointed at the middle of the tweeter at a distance of 50 cm.
Out of habit, we started by recording what the two parallel AXT 06 units were piping into the mic (left, red). At the end of the measurement process, two voice coils with 1.4-mm-thick wires and an Audyn electrolytic capacitor made the curve stick close to the 90 dB line (left, blue). The tweeter (red, right) also did well with the same order of filter, but designed as a high-pass filter made of two Audyn Q4 caps and a voice coil with 0.7-mm-thick wire. Since it was a little loud, though, at almost 93 dB, it was given a 4-watt Mox resistor that also tied it to the 90 dB line (blue, right). Connected in phase, it produced the ideal addition to the two branches, with a very small overlap. However, the crossover was only finished once an impedance correction – probably a requirement at 90 dB of volume – had been measured out.
The installation of the crossover and the chassis also seemed worth a few photos to us, with hidden captions.
Things got exciting in the listening room again, where for the first time the Axis 34 Neo needed to emit not just measurement notes, but music. Wanting to give a chance to something other than our wonderful tube amplifiers, we used the SAC pre-amp output combo of an Epsilon and two LaForza units to power the boxes. And they did it. When we put on the Bloomfield, Kooper and Stills Super Session “Season of the Witch,” for whatever reason, they laid into it with all the impetuousness of a horse long left forgotten in the stable. All right, it’s not an example of the finest high-resolution dynamics, but it took off like a maniac and we found we couldn’t leave the volume controls at their normal setting for too long – after all, there was still plenty of room to the right. Almost impossible, the pressure that came out of the two #17s, while still nicely differentiating every note of the bass drum and the bass. Despite the volume, the singer’s voice was unstrained, and the cymbal clashes didn’t hiss in our ears. That was a good start, with eleven minutes of widely varied music – the boxes were much more restrained, perched on their pedestals, than the listener on the old familiar sofa. As long as we’re talking about long pieces, we couldn’t quite agree with the title “I’m crying” on Erik Bourdon’s “That’s Live.” What the drummer did with his drums and cymbals during an almost six-minute solo might not have been as explosive as from a PA’s paper membrane, but it had plenty of bass and open space.Things were much calmer when we dug out Tracy Chapman’s 1998 Album of the Year to let it spin on our vinyl turntable. The track was “Fast Car” and the voice was pleasant – not too round or too thin, and the singer was clearly holding the guitar in her hands. Horowitz – not the one in Moscow, whose three-dimensional representation many listeners have enjoyed on our sofa, but the one in the New York studio – showed us very precisely and sensitively how Robert Schumann’s directions for Kreisleriana should be interpreted: the grand piano was very lively, intimate and not too fast; very lively, somewhat more lively, slower, very agitated; very slow, very lively, very slow; very fast, quick and playful, never betraying the advanced age of the man at the keyboard. There was not a note, a pedal movement or a decaying tone in the entire 31 minutes that was boring, hidden or in some way imprecise.
Kerpen, we have solved the problem – and yet the first sentence still applies: Kerpen, we have a problem. It just happens to be a new one. Where will we put the Axis 34 Neo, which showed no defects at all, loud or quiet; that always kept a clear overview, whether it was for rock, classical, calm or energetic music? How do you recognize a box that has so many good characteristics and still costs less than 200 euros with two excellent #17s and a seamlessly integrated ribbon tweeter, with the crossover and the rest of the rigamarole? After a good deal of indecision, we decided on the “Advanced” (“Climber”) class, but it was close to the Blues. We ended up wishing we had created many more classification levels. It definitely would have been the first reference in the lower “King” class.
Axis 34 Neo
|Chassis||2 x Gradient AXT 06||Woodlist in 19 mm MDF per box:|
|1 x Fountek NeoCD 3.5 H|
|29,8 x 55,8 (2x) Sides|
|Sales and||Intertechnik||29,8 x 19,0 (2x) lid/ floor|
|construction||52,0 x 19,0 (1x) back wall|
|50,0 x 19,0 (1x) Front|
|Function principle||Bass-reflex||14,0 x 19,0 (1x) Reflex board|
|Nominal impedance||4 Ohm|
|Damping/Insulation:||2 bags Sonofil||Milling depth|
|Terminal||T105/305MSAU||Bass/Mid: 4 mm|
|Tweeter: 3 mm|
|Approx. cost per box:|
|199 EUR/USD||Wood cutting: 15 EUR/USD|
|Frequency response and phase||Impedance||Frequency response under 0/ 30/ 60°|
|Distortion for 90 dB||Step response||Waterfall|
The complete assembling kit is available here.