Axis AX-HRArticle by Udo
These are one of the most popular types on the do-it-yourself market when it comes to good-value beginners’ boxes. With good reason, people who are new to building their own boxes appreciate the uncomplicated way their frequency response can be adjusted through volume compensation. At the same time, they are not afraid of putting together complicated-seeming cabinets, which often pose greater challenges than simple square boxes because of all their internal angles. What we’re talking about here, of course, are wide-range speakers; they are relatively uncommon on the market, but they come in all sizes ranging from very small to very large. In fact, they represent an ideal – producing every audible tone from a single chassis while still being completely simple to wire up. Naturally, it is easy to understand why they are still less popular in the hi-fi business. To create a decent level of bass notes and high notes at the same time, you have to make a lot of compromises. Deeper notes need more membrane size and weight, while high notes call for less moving mass and smaller dimensions – and those are just the most obvious requirements. The right resonant frequency and driver, efficiency and the appropriate parameters for good bass reproduction are other criteria that are always in conflict. The thankless task of the chassis builder is to combine as many positive characteristics as possible in order to send out all of the frequencies from one unit. Compared to a well-designed multi-path loudspeaker, that means many more hooks and eyes in the frequency response. The most obvious difference is in the channeling behavior: as the angle increases, the high range of the wide-range speaker quickly collapses due to the large sound-radiating surface. As full-range fans already know, the sound can still be fascinating. But many others can also benefit from thinking outside the usual two or three-way box; there’s no better way to get music from a single source than with a wide-range speaker.
Because of the many compromises that the all-in-one chassis developer had to make, wide-range speakers often don’t have traditional parameter sets the way a bass specialist does. Thus it is usually not enough to throw the data into a simulation program and let it calculate the cabinet dimensions. For instance, LspCAD told me that a cabinet with 248 liters and a reflex tube measuring just under 18 cm across and 16 cm long was ideal for the AX-8, and its calculations for the two other chassis elements weren’t especially user-friendly either. But if you think that caused me to give up on the idea of the reflex system, then you weren’t counting on the intervention of Armin Jost..
Sometimes the fates really do seem to be smiling on me – right when I finished doing the measurements for the Axis series, I got his email asking whether I would be interested in testing the new AJHorn Version 6.0. Its predecessor had helped us out of a jam at least twice during my time at a print magazine, when we were developing the Cheap Tricks. As you can see from the name, it’s especially well suited for calculating horns, which are one of the preferred cabinet types for wide-range speakers. But it can do much more than that – Armin Jost’s breakthrough was to treat all of the other types like horns, too. His extensive instructions clearly explain why that is and how you can apply it to the software. So far so good, but my problem was with the 248 liters and the 18 cm diameter of the reflex tube. What struck me as strange at first was the arbitrary way entries could be made anywhere in the field once the chassis data had been entered. After clicking on the Start button, a curve always appeared, although it barely resembled one. But when I asked myself what Armin might have been thinking with this strange line layout, I soon realized that a self-explanatory horn was appearing on the screen. The values to be entered are placed at the spots where they take effect. With a little bit of gut feeling and intuition, it was fairly easy to simulate a cabinet well beyond the common rules. It’s especially helpful that the user doesn’t need to type in a huge number of figures that often aren’t readily available, on a large number of pages. The software calculates many of them itself based on the information given in the field. The fact that complex frequency crossovers with two branches can now be calculated for the cabinets is a feature that many users have doubtless been waiting for, although it didn’t play a role in my simulation. I normally rely on my measurements for those; thanks to the huge number of components that we have available in every quality class, I can try out the effects in real life. Armin Jost’s homepage offers extensive information about the other updates in Version 6. The 119 euros he is charging for AJHorn are a good investment for box-builders – unlike other programs, the software provides reliable results not just for specialized measurement data from a single manufacturer. If you want to try out the program before making a decision, you can also download the demo version with limited features, or read the extensive manual.
I couldn’t come up with a real horn in a reasonable size, so I got to work designing something in the CT193 range using AJHorn. Heinz Schmitt had once designed a structure with an unusual reflex channel, starting with a very small input and ending up ten times larger. That turned my bathtub design for the AX-8 á la LspCAD into a handy free-standing box with a total of 78 liters of enclosed space and a channel with a parabolic opening, which I called a horn reflex like the earlier design. For the sake of simplicity, I just made sure the input and output of the resonator had the right area, and installed a diagonal board in the box instead of a precisely customized contour. Comparing the simulation with the final product shows that neither I nor the software were wrong in our calculations; the comparison is given at the end of the report as a measured amplitude diagram.
Einmal an die genial einfache Bedienung von AJHorn gewöhnt, fand ich auch für die beiden kleineren AX-Chassis geeignete Gehäuse in gleicher Strickweise. Der AX-5 fand 20 Liter ausreichend, der AX-6 gab sich mit 35 Litern zufrieden.
Drawings as Sketchup-file
To make sure that the cabinet construction isn’t overlooked, here are a few small pictures. Click to expand them to a more visible size and to read the corresponding text.
I continued with the AX-6 HR, which by now had dried and been sanded and routed.
The AX-8 HR requires two Sonofil mats, which are available in dimensions of 100 x 35 cm. For the small AX-5, a mat is cut in half to 50 x 35 cm.
What is the best-known application for wide-range speakers measuring 20 cm? Any member of a hi-fi forum would immediately mention the “Viech.” As soon as the preliminary test results were released, the AX-8 was naturally included in the long list of candidates for this fun, beloved box, which made us very happy. However, since most users hardly have any measurement tools, let alone owning various types for comparison, it was up to us to throw the AX-8 into the now almost legendary horn and put it in front of the microphone. Once again, I met with a helpful coincidence; when I showed Stefan the measurement sample, he mentioned that his set of Viechs, equipped with one of the best drivers for the job, was currently standing around in the storage closet looking for work. He said he always used it with this chassis without any protective circuits. On a day when there was a break in the rain, he loaded it into his trailer and let me set it up in the shop for a couple of weeks, where naturally I listened to it right away and started taking measurements. For further comparison, I also found the measurements for the original Viech with an anti-resonant circuit, which I had once made for K+T using my equipment. Together with the AX-8 correction, that made three. Aside from the volume level, the AX-8 has nothing to be ashamed of. It gives the Viech owner significantly more body and height than the two comparison types, which are distinguished more by their slight emphasis on the middle range.
Like almost every wide-range speaker, our Axis series also required a small correction in the frequency response. Both the baffle-board width and the strong channeling at the top with rapidly increasing volume needed to be balanced out. Let’s look at the example of the AX-8 already tested in the Viech, which was now creating the green sound pressure in its horn reflex housing. An upstream coil lowers the volume above 400 Hz, but on principle that makes it constant due to its increasing resistance of 6 dB per octave. That doesn’t leave much room in the high range for anything to gladden the ears. A resistor soldered above it is helpful here; it only lets the impedance increase slightly at high frequencies, creating the right volume level in this area (red) given the right dimensions. Compared with the green line, it looks pretty good, but there are still three peaks between 3 and 5 kHz that hit the ear in a sensitive place. A suction circuit made of a series-connected resistor, coil and capacitor is just the ticket here for preventing injuries to the ear canal. The result was the blue line, which still shows a strong increase above 8 kHz, but at any angle less than 15 degrees this exaggeration disappears again. The slight waves in the amplitude diagram are mainly due to the fluttering cone, which slightly modulates parts of the mid-range tone radiated from the main membrane. This is more apparent in the AX-5 because of its smaller membrane, but because of its very small bandwidth it cannot be detected by the human ear. If the cone could duck out, the waves would nearly disappear, but so would most of the high range. A dust-cover cap could be helpful here, but it would be a disadvantage in other areas. What was I saying earlier about wide-range speakers? They only work if you can compromise – and that’s before we even get to the sound description. In the Axis series, everything worked very well together.
Naturally, I did my first listening test with the smallest unit, AX-5 HR, which I had cobbled together in cost-effective stereo with my Yamaha-AV. According to its nature, it magically reproduced the deep stage in my room. It impressed me with its bass reproduction, which was actually a bit inappropriate for its size but very contoured and transparent. Wonderfully freed from the boxes, voices and all kinds of instruments made their way to the listener; terms like “annoyance” and “discoloration” were foreign to it. It easily handles being close to the wall, which is usually the case for its natural listening environment in a teenager’s room, dorm or home office. But even free-standing in my 42 m² room with a 4 m ceiling, the little guy felt right at home; only the direct comparison with the AX-6 HR showed that there was even more potential around the bottom section. With its almost doubled membrane area and the nearly 15 Hz lower resonant frequency, it smilingly showed its little sister what was possible once you grow up. It added a little bit more to the amazing features we had already seen: depth, pressure, dynamics and volume reserves. With just two dB of increased sound pressure at the same amplifier settings, it was able to get even louder without sounding hoarse. It never gave me the feeling of listening to a cheap wide-range speaker, even though the Axis series could rightfully be called cheap in terms of the price. Much of this is also thanks to the cabinet, and I want to once again specifically thank Armin Jost here for providing its calculation basis.
And then, as so often, three of us were sitting on my sofa and reverently listening to the Duetta’s performance when Stefan’s curiosity got the better of him; he disrupted our idyll and spontaneously paid me a visit as promised a few days earlier. Naturally I had already emailed him to say that the AX-8 HR was assembled and waiting for him to hear it. Since he had selflessly lent me his Viech, he needed be the first one to give his verdict on the new pint-size assembly kit. In any case, I was hoping for a couple of observations that I could use in my sound review. So we disconnected the Duetta, moved the AX-8 HR to the place of honor and had Stefan sit in the middle. With “Hotel California,” overplayed but still good, the Eagles gave him something to chew on. Guitars on the left, guitars on the right, then a shudder ran through all three of my guests as the drum went “boom.” Stefan’s eyes gleamed as he commented, “Whoa! I wouldn’t have believed it if I had just read it in a magazine. The Viech doesn’t stand a chance here!” What he meant, of course, was the deep, heavy impact that he hadn’t expected to hear from the housing, delicate compared to the Viech, with its precise attack and rolling, echoing thunder. The other two visitors, having already been spoiled by Duetta & Co. for a couple of hours, had put on their best sympathetic smiles when we connected the AX-8 HR, but they soon turned to appreciative grins. Then we were able to enjoy a couple of less spectacular pieces, which themselves inspired Lutz’s brief commentary for the chassis test: “AWESOME! WANNA HAVE!” When I asked him to write just a little bit more, he summarized the impressions from his first visit to the halls often described, with some exaggeration, as “sacred”: “So little money for so much space – every landlord is going to go broke. ;) And, probably thanks to the simply ingenious construction around this chassis, there’s a nice, deep, bone-dry bass! Dynamics and a wealth of detail, as with your other boxes, are as essential here as a door for a car. As soon as the assembly kit is ready, I’m in!” What else is there to say?
|Chassis||Axis AX-5||Wood list per box in 19 mm OSB:|
|104,0 x 26,0 (2x) sides|
|15,0 x 26,0 (3x) lid/floor|
|Sales||Intertechnik||15,0 x 65,0 (1x) rear wall|
|Construction||Udo Wohlgemuth||15,0 x 55,8 (1x) front(baffle) (one corner 23,0 °)|
|15,0 x 21,0 (1x) reflex board|
|Principle||Horn reflex||15,0 x 10,0 (3x) reinforcement|
|Nom. impedance||8 Ohm|
|Insulation||1/2 mat Sonofil||The reflexboard is cur from:|
|Terminal||T 105 AU/ MS||
15,0 x 21,0 cmIt has two corners.
|Angle measurement with 23,0 ° and measures|
|Cost per box approx.||15,0 x 18,6 cm after cutting|
|Wood cut: 15 EUR / 16 USD|
|Chassis||Axis AX-6||Wood list per box in 19 mm OSB:|
|104,0 x 32,0 (2x) sides|
|18,0 x 32,0 (3x) lid/floor|
|Sales||Intertechnik||18,0 x 81,2 (1x) rear wall|
|Construction||Udo Wohlgemuth||18,0 x 67,2 (1x) front (one corner:23,5 °)|
|18,0 x 30,0 (1x) reflex board|
|Principle||Horn reflex||18,0 x 10,0 (3x) reinforcement|
|Nom. impedance||8 Ohm|
|Insulation||1 mat Sonofil||The reflex board is cut from:|
|Terminal||T 105 AU/ MS||18,0 x 30,0 (1x). It has two corners|
|measuring 23,5 ° and measures|
|Approx. cost per box:||18,0 x 26,9 cm after cutting|
|wood cut: 18 EUR / 19 USD|
|Chassis||Axis AX-8||Wood list in 19 mm OSB:|
|104,0 x 40,0 (2x) sides|
|22,2 x 40,0 (2x) lidl/floor|
|Sales||Intertechnik||22,2 x 100,2 (1x) rear wall|
|Construction||Udo Wohlgemuth||22,2 x 81,2 (1x) front (one corner angle :29,0°)|
|22,2 x 38,0 (1x) reflex board|
|Principle||Horn reflex||22,2 x 10,0 (3x) reinforcement|
|Nom. impedance||8 Ohm|
|Insulation||2 mats Sonofil||The reflex borad is cutfrom:|
|Terminal||T 105 AU/ MS||22,2 x 38,0 (1x). It has two corners|
|Measuring 29,0 ° and measures|
|Approx. cost per box||22,2 x 35,4 cm after cutting|
|Wood cut: 22 EUR / 24USD|