They say things were better in the old days; in particular, loudspeakers still acted on their own behalf, and they could out out a decent volume even with low-performing amplifiers. Today things have gotten quiet around the high-output bass and mid-range speakers, the result of striving for a slimmer figure even for loudspeaker boxes. With fifteen or even eighteen-inch speakers at 200 liters and a 65-cm-wide baffle board, no one can – or to be honest, wants to – blast the living room with sound anymore just because it’s considered manly. So that species of loudspeaker gradually died out, and hardly anyone noticed. Well, all right, the big boxes were certainly hard to work with when decorating a living room. Whether or not they were beautiful is in the eye of the beholder.
With the growing output even from small amplifiers, the production of loud chassis elements with hi-fi-appropriate dimensions unfortunately declined, too. Today there are only a handful left, with much more than 90 dB and a maximum of 8 inches, that can still be satisfied with narrow boards. When we complained about this situation in Kerpen, Patrick Even immediately followed up with the supplier of the Axis series and had samples built in two sizes according to his specifications, which were quickly ready for series production. It was only our lack of time that forced them to vegetate much too long in the warehouse; they were finally introduced in the magazine in early July, in the chassis test. Now the first assembly kit is finished – in keeping with the rest of the program, we are calling it the “Power 17.”
Now that the name is set, it’s time to start thinking about the development goal – you don’t just build a loudspeaker on a whim, without a real need. We saw that need in a few questions that reached us in the forum and by email. Again and again, people asked about a mobile solution, if possible using DTA-1, that could be used as a construction-site/workshop box or for small parties and festivals. If the speaker can also be used for music at casual hangouts in the garage after work, that already gives us three good reasons to invent it. Because people who use low-wattage tubes have also been asking about high-performance boxes recently, there’s room for a Power 17 in that area too, which would be much more challenging than your basic party box. But if we don’t take on that challenge, we’ll never know whether the unusual combination would work.
The next step involves thinking some more about the properties of this kind of construction. Huge dimensions are somewhat counter-productive, and the same is true of heavy weights. The request was for something compact, but a little bass wouldn’t be bad either. For the Gradient AXP 6, LapCAD called for 11 liters of reflex volume, but under 100 Hz all it produced was lukewarm air. Once we added another 7 liters, it predicted a good 87 dB around 60 Hz in a free field. That was worth building. From our assortment of suitable tweeters, we went back to the P.Audio PHT 416, a very affordable horn with a titanium membrane and an elliptical attachment, which according to the manufacturer can be used starting at 1.5 kHz. Naturally, its measurement data will be included in this report.
P.Audio PHT 416
Item No. 1411528
|Membrane:||Titan||effective membrane surface:||5 mm²|
|Voice coil:||25,4 mm||Pole piece hole:||no|
|Winding heigth:||1,5 mm||Mounting holes:||4|
|Pole piece thickness:||3 mm||Magnet:||Ferrite|
|Qts||1,17||SPL 2,83V/ 1m||100||dB|
|Frequency under 0/ 30/ 60°|
|Distortion for 90 dB||Step response||Waterfall|
Once all of the data had been gathered, it was time to start drawing the cabinet. Once again, SketchUp – the free drawing program that our readers can use to look at and modify our assembly plans on their own computers – came in handy.
We had the wood cut to size at the hardware store, and the CNC milling machine took care of the cutouts. Then all we had to do was create a reasonable 3-D shape out of the two seven-piece wooden puzzles. The first attempt was well and truly a disaster. We used the front panel with the cutouts on the inside, which would have kept us from putting the chassis in the right place after gluing it. Fortunately, you can still separate the joint glue with a little force, but without damaging the wood, after about 10 minutes. We decided to take some new pictures anyway.
We are proud to present our new assistant Luca, whom we were able to photograph during his first job for the magazine. He’s still having some trouble arranging his feet on the box so that the weight is evenly distributed. But it’s a good start, and we’re sure he will be a big help in the future.
Since the tonal results had only been predicted in a fairly meaningless simulation at that point, we put together the crossover before giving the cabinet a halfway decent surface. If we told you it was an easy endeavor, that would be a bold-faced lie; above 300 Hz, the frequency curve for the bass rose consistently to around 8 kHz, by nearly 10 dB. We balanced it out with a coil whose effect was lessened toward the top by an overlaid resistor. After that, a 12 dB filter was enough to make the turn at 4.5 kHz. The cone gives the tweeter a strong volume increase of 8 dB below 10 kHz, and at 2 kHz it drops off evenly again. With a third-order filter and a voltage divider, it happily joins up with the AXP 6 at about 5 kHz, as you can see from the branch/overall diagram.
For the owners of the abovementioned tubes, of course, it also made sense to measure the impedance correction. The three components were attached to the terminal in front of the crossover in a parallel circuit; the sequence is not specified. They perform the same function at every point in the suction circuit, and they work together to smooth out the peak in the separation frequency. The correction components are included in the assembly kit.
|Frequency under 0/ 30/ 60°|
|Distortion for 90 dB||Step response||Waterfall|
Now there was nothing standing in the way of beautifying the raw MDF boards. So we took the chassis back out, sanded off the projecting edges and traces of glue, and rolled a coat of white wall paint over the whole thing. Next, we immediately sprayed the wet surface with a can of stone-finish paint, and voila – the boxes were beautified for just 8 euros. If you want, you can also add a coat of clear varnish once the paint is dry. At the end of the assembly process, we put everything back in the boxes, glued the parts down and screwed them in. That included the crossover, which goes on the side in the back between the bass mid-range speaker and the tweeter, and two bags of Sonofil, which loosely fill in the whole interior of the box.
It’s hard to find the positive pole of the horn – it is stamped on the rim bracket and is on the left when you are looking at the magnet of the PHT 416. In the AXP 6, the wide rim marks the positive connection. Before screwing on the chassis, the foresighted box-builder should use a small drill bit to pre-drill some holes for the screws.
The last phase of every box development process is the listening test – this time, it was done with a variety of amplifiers. This was due to the various applications of the Power 17, but it was also due to coincidence, which brought several potential users of the new construction to our shop at once. First there were Kathia and Alexander and their daughter Julia, from Neumarkt/Oberpfalz, who brought along their AVR and a piece of music. They wanted to connect a kitchen sound system to the second zone of the amplifier, and the Power 17 quickly filled the need. When Ilja and his buddy wandered in a short time later, they were carrying a construction-site “radio” equipped with small boxes and a DTA-1, which was a little too quiet with a cell phone as the source. The Power 17s were bigger than the little boxes they had installed before, but when it sounds that much better, the three extra kilos are easy to handle.
Bausatz Power 17
|loudspeaker drivers||Gradient AXP 6||Wood list per box|
|P.Audio PHT 416||in 19 mm MDF:|
|Sales/construction||Intertechnik||26,0 x 39,0 (2x) baffle/ backwall|
|24,0 x 39,0 (2x) sides|
|24,0 x 22,2 (2x) lid/ floor|
|Function principle||Bass reflex||10,0 x 22,2 (1x) reflex board|
|Nominal impedance||8 ohm|
|Connecting terminal||T104 low cost||Milling:|
|Damping/insulation||2 bags Sonofil||mid/woofer: 5,0 mm|
|tweeter: 4,0 mm|
|Approx. price:||120,-||terminal: 3,0 mm|