AX-HR Axis-Hornreflex

Gradient Axis AX 5 / 6 /8

--> 15 cm full range Axis 5 with horn-reflex tuning
--> Lower cut-off frequency in horn-reflex with 18 cm full-range driver Axis 6
--> Even more bass in horn reflex with 22 cm full-range driver Axis 8

Full-range loudspeakers for the more or less entire frequency range are among the most popular loudspeaker drivers on the do-it-yourself market - especially in the entry-level segment, because do-it-yourself starters appreciate the low price and the usually quite simple filter network - which can even be dispensed with altogether in the case of a high-quality (digital) equaliser, but this is usually more expensive than the few components needed for passive equalisation. The downside of full-range speakers is that they rarely fit into a simple square box; usually at least a bass reflex system is required and, even better, a bass horn - or, as here, a combination of both. Technically less experienced beginners are more than willing to put up with the complicated construction, even if there are various boards inside that need to be mitred.
 

 

Due to the necessary compromise-avoiding development approach, full-range drivers often have anything but classic parameter sets - it would be just too good if these all-rounders were bass, midrange and treble specialists at the same time. Since full-range drivers are seldom among the most inefficient drivers, one has to help the bass reproduction with special cabinet designs.

In any case, it's not a good idea to simply enter the Thiele-Small parameters of the full-range drivers into a simulation programme, because, for example, it calculated for the AX-8 a huge cabinet with 248 litres net volume and a bass reflex tube with a diameter of 18 cm and a length of 16 cm. Wait a minute, we need an enclosure for an 8-inch speaker, not for an 80 cm driver! The calculations for the other two full-range drivers were no more practical.

Housing

Thanks to Armin Jost we didn't have to give up the idea of the Reflex system, because when we had just finished testing the Axis series, we received an e-mail asking if we were interested in testing the new AJHorn version 6.0. Sure, why not? Its predecessor had already bailed us out twice. As you can easily guess from the name, it is excellently suited for calculating horns, one of the preferred dwellings of the common full-range driver.



But it got much better: Armin Jost has dared to understand all other types of construction as horns as well. In his detailed instructions, he describes in an easily understandable way why this is so and how to use this in the software. So far, so good, but our problem we wanted to get rid of was 248 litres and 18 cm bass reflex tube diameter. The input screen of AJHorn version 6.0 seems anything but tidy, but that has a point:

After entering the relevant parameters, AJHorn draws a curve that represents a self-explanatory horn where the parameters are placed where they have an effect. This is very well thought-out, because with a little experience it is quite easy to calculate an enclosure in this way, even off the beaten track. Fortunately, as a user you can enter the data directly, without having to make settings and entries on several pages and submenus, which you first have to painstakingly search for or which are not available to you at all. The software itself takes over a large part of the complex calculations on the basis of a few entries in the input mask.

The fact that complex crossovers or correction networks can now also be calculated does not play a role in the cabinet simulation, but it makes the later tuning easier for many users, since not everyone has the necessary measuring equipment and the corresponding selection of components for a multiple adjustment of the tuning.

Further innovations of version 6 can be found in detail on Armin Jost's homepage. The 120 Euros for AJHorn are well invested for loudspeaker builders: In contrast to other programmes, the software does not only deliver reliable results with the specialised measurement data of a single manufacturer, but can be used quite universally. Those who are still apprehensive can first have a look at the offered demo version (with limited functionality) together with the manual, which is also available for download. What is true for the LspCAD simulation is also true for a real bass horn: it will be huge. So, with the help of the AJHorn simulation programme, we thought up a mixed cabinet shape. Many years ago, Heinz Schmitt had already designed a structure with an unusual reflex channel that started with a very small inlet and ended as a tenfold. Helmut Lengefeld also used this bass reflex port in the past and called it horn throat, as did Hans Deutsch at his former company ATL.

In the case of the AX-8, this shrank the enormous dimensions to a handy 78 litres net volume in the form of a slim floorstanding speaker. At that time we called the parabolic opening channel a horn reflex. In this case, we kept the dimensions to the resonator's input and output area and replaced the parabolic channel with a simple slant. The fact that we obviously not only used AJHorn correctly, but that it also delivered a correct calculation, became apparent later when we measured the frequency response.

So we liked the ultimately very simple operation of AJHorn version 6.0 and dimensioned similar cabinets with 20 and 35 litres net volume for the two smaller full range drivers AX-5 and AX-6.



 

Construction

 For self-assembly beginners, we have again documented the assembly photographically. Please click on the respective picture for a larger view, then the corresponding text is also readable.





The next step was the AX-6 HR, which had already been dried, sanded and milled in the meantime.

The AX-8 HR needs two mats of Sonofil, the AX-6 one and for the small AX-5 one mat is cut in half to 50 x 35 cm.

First curiosity

Who among serious loudspeaker builders doesn't know it, the best-known application for 20 cm full-range drivers? Some people will immediately think of the "beast" in which our customers also installed the AX-8 directly after the release and publication of the chassis data including the corresponding measurement results, which of course made us very happy. However, since most self-builders don't have professional measuring equipment and usually only a few comparable drivers for sound comparisons, it was up to us to be the first to put the AX-8 into the almost legendary horn and put it in front of the microphone.

So it was a good thing that a customer had a pair of the best-known drivers for this purpose, without any wiring (which is generally not done with these drivers), just lying around in the storeroom and put them in our listening room for a few weeks. Of course, they were heard and measured immediately. For further comparison we used the measurement for a print magazine of the original, with a wave trap, so we can now compare three measurements with each other, whereby the AX-8 was also equipped with a correction network.

If we disregard the efficiency, the AX-8 can more than keep up: With it, the Viech owner has significantly more fundamental tone and treble than with the two comparison types, which are more noticeable for their slight midrange emphasis. Who would have thought that?

In principle, you can run full-range speakers without a correction filter, but from a hi-fi point of view you should not necessarily do without it. A small frequency response correction is also very useful with our Axis full-range drivers. The AX-8, already tested in the Viech, showed the green sound pressure curve in a horn reflex cabinet. A coil in front of it lowers the level above 400 Hz by 6 dB/oct., which a resistor connected in parallel to the coil absorbs towards high frequencies and thus straightens the level curve if correctly dimensioned (red curve).

Compared to the green curve, this already looks quite good, but the three jags between 3 and 5 kHz not only catch the eye, but also the ear, as our hearing is particularly sensitive to amplitude fluctuations in this range. A suction circuit consisting of a series circuit of a resistor, a coil and a capacitor helps against this. In the end, it sounds more pleasant this way. The result of this sound cure was the blue curve, which still rises above 8 kHz, but only measured on axis. Already at a measuring angle of 15 degrees this rise disappeared. With the right placement (a little more angled) this results in a very good dispersion even for several listening positions, alone the speakers can be aligned a little straighter. The ripple in the amplitude frequency response is negligible, it is caused by the tweeter cone. Due to its smaller diaphragm, the AX-5 is more pleasing, it is at its best in jazz even without a correction network, its narrow band notch is practically hidden from the ear.

Measurements AX-5 HR

Measurements AX-6 HR

Measurements AX-8 HR

This is why chassis designers place so much emphasis on the correct dimensioning of the tweeter cone and on the decision whether to use a dust dome or a phase plug. Both have advantages and disadvantages, so in the end the best compromise has to be found. With the Axis series, everything fits together very well, which was confirmed in the sound test.

Sound

We started the test with the smallest of the three slim floorstanding speakers, the AX-5 HR, connected to a matching amplifier. As expected, the AX-5 HR reproduced a deep stage in our listening room and convinced with a substantial bass reproduction that didn't quite match the tiny size of the full range driver. The bass was not abysmally deep, but very contoured and clean.

Voices and all kinds of instruments sounded completely detached from the stand-alone speakers, the terms "annoyance" or "colouration" were fortunately left out of the equation. Unusual and special for a floorstanding speaker is the possibility to place it close to the wall - which is a real advantage considering its probable use in a youth, student or study room.

But even free-standing in our large listening room, the little one felt right at home and only a direct comparison with the next larger AX-6 HR revealed that the low bass can be even more powerful. With almost twice the diaphragm area and a resonance frequency almost 15 Hz lower, the middle of the three sisters showed the little one where it's at when you're big. So there was a little more of everything that had already amazed the little one: More depth, more bass pressure and a lot of additional level stability, combined with a correspondingly dynamic sound. It's not just the higher power handling, but also the two decibels more efficiency, especially at higher "room volumes". It was astonishing how mature the speaker was, not a trace of a cheap full range driver, even if the Axis series can be called that at this price. Once again, a properly dimensioned floorstanding speaker is more than just a compact speaker with an integrated stand, and we would like to thank Armin Jost for his calculations.