As we know, beauty is in the eye of the beholder, and beautiful sounds are in the ear of the listener. In the area of loudspeaker building, for whatever reason, we have gotten used to placing much more emphasis on the second part of that statement than the first. That means a great deal of attention is paid to diagram-readers; all of the jumps in the measurement curve are smoothed out, and the baffle board in particular is designed with the greatest of care. Form follows function, is how this fainthearted construction nonsense is explained away. However, the fact is that music furniture will spend most of its life in someone’s living room, in keeping with the second half of its name. Is it allowed to be ugly just because it sounds nice? “No!” is the much-too-rare answer, “we can do better.” As long as the sound doesn’t noticeably suffer, a compromise can be found that doesn’t require squaring the circle. In this case, we didn’t have to fit a round peg into a square hole, just an oval into a trapezoid, so to speak.
How did we come to this unusual realization, which surely no one expects from a loudspeaker magazine? On the search for new project ideas, we found a beautifully shaped pair of triangular multiplex cabinets in the basement that we hated to throw away. Since they had already had a former life of a kind, there were already chassis cutouts that had long been empty. The successors needed to be the same size, neither smaller nor larger, but the specifications called for a #17 and a tweeter. Now a CNC router had been purchased, with good reason, but unfortunately it couldn’t handle the finished triangles. Still, new chassis holders would not be a problem. Black-stained MDF contrasts nicely with light multiplex, and to make sure it didn’t look like an artificial distraction, it was rounded throughout. The pre-existing reflex tube cutout was too big, so we added a collar made from the most regular form of an oval – a circle. That way the eye has something to look at on the top and the bottom; whether or not it is pleased, is just … see above.
Now there were plenty of options for filling the basement cabinet with new life – its 18-liter volume and baffle-board width would work with almost all of our seven-inch speakers. The Duetta Top light had never really been presented here, and Matthias had already done the SB 18 as a triangle. The Quickly 18 already has two cabinets for both versions, and let’s not forget the Kera 360.1 from the drawer and the Feel IT, which has been unfairly overlooked due to a lack of discussion. From Seas, we could also use the MS 3 MK2, Bifrost, Nextel 18 or Minimax. The Audible 17 is ruled out because of its square tweeter, but now we’re getting close. The Gradient AXT 06 is still without a home of its own – until now, it has shared a place with its twin. In addition, the AXD 97 NF developed for the Axis chassis has been languishing without much to do, and the unusual shape of the Axis 15 means that it is not one of our bigger sellers. With that, the components of the new loudspeaker were clear. Even the name was predestined: Gradient in a Triangle is a little long, so we chose the abbreviation Triagra.
One of the simplest jobs in building a loudspeaker is gluing together your three-sided wooden crate. All you need is a circular saw. That gives the boards to be glued together a 30-degree angle on each side, and then they practically go together on their own. The pictures speak for themselves.
After the gluing, a square lid is attached, which the trimming cutter easily turns into the right shape. To be safe, the foot should be slightly larger than the base of the triangle. To make it, place the box on a large enough board and use a rod laid against the walls to trace the cutting lines. The circular saw will then know exactly how much space to leave.
As mentioned above, the little 120-cm-tall box was already finished before we started thinking about the Triagra, but as in life, sometimes objects are invented for something completely different and then only used for their coincidental side effects. So it should not surprise anyone that multiplex appears as a construction material later on even though MDF was obviously attached earlier. The additional front and the reflex tube adjustment had to be glued to the baffle board before any further steps were taken.
After 20 minutes, everything had set firmly enough that a biwiring terminal with long wires to the bass and tweeter could be screwed into the side and a bag of Sonofil could temporarily go into the box. The chassis elements and the HP 50, shortened to 8 cm, were installed, and then it was time to develop the crossover. As usual, the loudspeakers were measured in the box, which gave us a starting point for the effects of the attached baffle board and the desired separation frequency.
The board, projecting outward nearly 2 cm, is not very significant for the AXT 06. It is already too concentrated at the top and the sound waves are too long on the bottom, so the little offset is practically invisible. Of course, it is a different matter for the tweeter, and at first I wondered whether I could even expect the diagram interpreters to accept the strong dip at 4300 Hz. There’s a real hole of 10 dB in the frequency curve! The reason for the dip is easily explained when we keep in mind the sound radiation from the tweeter. The sound radiates in all directions and reflects off the inset front; at 4.3 kHz, it is the most out of phase with the direct sound. As a result, there is a notch in the curve for the on-axis measurement. However, this phenomenon is not unique to the double front – it happens with every baffle board. If you make it wide enough that all of the sound waves coming from the tweeter are reflected, up to its separation frequency, there is almost no way to keep it under 30 cm. Whether or not you want that in your living room is a matter of opinion, and usually there is not just a strong opinion, but also a weak one. But wait, we’re getting to the solution for the visible problem that doesn’t involve a compromise. As the angle increases, the dips disappear, which is why we generally – with the exception of the broadband units – recommend setting our loudspeakers up parallel to the side walls.
Now we come to the real issue in developing a crossover, namely developing the crossover. The curve of the AXT 06 inspired us to try a combination of a series core coil and a parallel capacitor, which worked right away. Some of the volume was taken away from the tweeter, and then a series capacitor and a parallel coil rounded out the job. The separation is at 2.5 kHz, which can be seen clearly in the overall branch curve because the addition of the branches is nearly perfect when the chassis elements are connected in phaset.
In order to further smooth out the hook at 4.3 kHz, we added seven measurements from 0 to 90 degrees that roughly show what the box will project into the room. The result was a curve that was fairly predictable despite the spectacular dip.
With good reason, tradition has it that we also keep tube listeners in mind. So the impedance was smoothed for the Triagra, too, using an upstream suction circuit.
|Frequency under 0/ 30/ 60°|
|Distortionfor 90 dB||Step response||Waterfall|
In order to test the pair of boxes for ourselves in the listening room, there were still a couple of steps left.
Before the Sonofil™ could be loosely packed into the box, the crossover was glued to the side wall under the tweeter, and the shortened reflex tube was set into the collar. We screwed in three RS-07/22 rubber feet under each loudspeaker – available from Intertechnik in packs of 20 for just under 4 euros.
Without further delay, we now moved to the final act – the listening test. Anyone who expected the Triagra to play everything that we had lying around in the listening room, effortlessly from top to bottom, should read a different magazine. We don’t use meaningless superlatives, which can lead to justified disappointment in listening tests. The bass is not extraordinarily deep, but it is crisp, and a bass drum can easily be distinguished from an electric bass. It is not excessively loud either, so the box can be set up close to a wall. All in all, the Triagra does not offer any more in this frequency range than any good 17-incher can offer, but it refreshingly refrains from trying to be spectacular. The mid-range is equally balanced, to the extent that you can consider it on its own. The stage falls behind the line where the loudspeakers are set up, and the locatability and detachment of the speakers leaves no room for complaints.
If anything in particular stands out in the very balanced representation of music, it is the upper frequency range, which the AXD 97 NF handles really well. It’s hard to say why I decided to listen to the old CD “In the Court of the Crimson King” – it just fell into my hands. Whether or not listening to the improvised, percussive tones of “Moonchild” for ten minutes is recommended remains to be seen. However, it clearly showed how precisely the cost-effective tweeter can reproduce fine details. When we listened to the Axis 15 for the first – and to date the last – time, the goal for the box was different, and playing music through a PC and DTA-1 via internet charts was no great challenge.
After this listening test, We have to give it a pat on the back. It can do a lot more than we asked of it at the time. With renewed confidence, We quickly went over to classical music, jazz, rock and everything else (except German pop hits) that my CD and record collection could offer. However, there were no weaknesses to report in the Triagra even after this longer listening session. So the eye and the ear are in accord, just as we expected. And before you ask: of course the cabinet doesn’t have to be triangular with an additional front attached. A good old conventional square box will do it too, as long as it offers roughly 18 liters of volume.
|Loudspeaker drivers||Gradient Axis AXT 06||Woodlist in 18 mm Multiplex:|
|Gradient Axis AXD 97 NF|
|120,0 x 23,4 (6x) sides (30° beveled)|
|Construction/sales||Intertechnik||21,2 x 24,5 (2x) lid (isosceles triangle)|
|30,5 x 26,0 (2x) feet (floor)|
|Function principle||Bass-reflex||Routing depths for milling:
|Nominal impedance||8 ohms||Bass: 4,2 mm|
|Connecting terminal||Intertechnik T122 MS/AU||Tweeter: 6,2 mm|
|Damping/insulation||1 bag Sonofil™|
IT HP 50 shortened to 8cm