SB 417Article by Udo
Building loudspeakers is no different from real life: there are winners and losers. The second category definitely includes the SB 17 RNXC-4, the four-ohm version of the beloved bass mid-range speaker from the SB 18, SB 36 and the SB 240. Here we can already see that the brother has claimed all of the spots, leaving almost no room for its structurally almost identical twin to demonstrate its usefulness to the world. What are you supposed to do with it, anyway? It’s no good for the SB 36, and no one needs an SB 18 assembly kit with fewer ohms – especially not when today’s AV receivers prefer 8 ohms. We consider the multi-channel trend to be irreversible, so it is becoming more and more important to invent coordinating sets of different-sized loudspeakers where the individuals don’t have any chance of self-actualization. Still, as habitual stereo listeners, we can see another niche where this previously overlooked device would fit in well. Following the standard terminology, we gave it the explanatory name SB 417. And just to say it loud and clear right at the start: we really don’t care whether this assembly suggestion will also work for a home theater, be it for films or to fulfill the female acceptance factor. It was designed exclusively for enjoying music in good old stereo, and there’s no need to debate that.
Even at first glance, it’s immediately clear which family the SB 17 RNXC-4 belongs to. The characteristically tall basket rim is common to all of the SB chassis elements, along with the shimmering gray-black color of the smooth paper membrane and the highly curved dust cover in the same color. The rubber surround material promises a significant lift, while the high-set, rear-ventilated centering piece reveals the 16-mm-tall 35.5 mm voice coil made of copper-coated aluminum wire on a fiberglass base. The enormous magnet, with a 10-cm diameter, has a large pole-piece hole; the air vent is 5 mm tall, so the linear lift is a full 11 mm. A copper plate on the pole piece ensures low inductivity and efficiently reduces noise. Since we haven’t even introduced the SB 17 RNXC-4 in a chassis test before, we will use this report to tell you about the data we measured for it.
Data sheet, SB-Acoustics SB 17NRXC-4
Order No.: 1382313
Measurements as a zip-file
|Membrane:||cardboard, impregnated||Air gap height:||5 mm|
|Surround:||rubber||Linear excursion:||11 mm|
|Basket:||Die-cast||Magnet diameter:||100 mm|
|Pole piece hole:||yes||Mounting holes:||4|
|Centering:||Raised flat spider||Outside diameter:||171 mm|
|magnetic shielding:||no||Installation opening:||144 mm|
|Voice coil:||35,5 mm||Milling depth:||6,5 mm|
|Voice coil former:||Fiberglass||Installation depth:||81,5 mm|
|Frequency response and phase||Impedance||Frequency response under 0/ 30/ 60°°|
|Distortion for 90 dB||Step response||Waterfall|
Since the bass mid-range speaker can’t make all of the music by itself, it needs to be supplemented by a tweeter at the top. To avoid getting bored, we decided to use the SB 26 STAC-4 here, which is almost identical with the SB18 tweeter except for the aluminum front, but has never been used before except in the SB 23/3. That’s because the metal plate makes it about 10 euros more expensive than its brother without the “A,” and whenever the performance is the same we generally reach for the less expensive product. But because of the high demand for the SB 18, 36 and 240, not to mention the blueSBox, it is constantly sold out; so this time we went with the more expensive model that would usually be left gathering dust. You can find the data sheet for the SB 26 STAC-4 in the March 2010 issue.
Of course we haven’t forgotten to mention it, even if we didn’t exactly spell it out. Because we didn’t want to invent a four-ohm SB 18 and because an SB 36 is out of the question for the basses anyway, it makes sense that the SB 417 would have not one, not two, but four SB 17-4s, as we will call them for short. At 15 liters per bass, that comes out to a pedestal with roughly 60 liters. The distribution of the chassis elements from top to bottom with bass, bass, mid-range speaker, tweeter and another bass mid-range speaker calls for a height of 120 cm. The width of the SB 17-4 requires a 19-cm interior dimension for the baffle board, which then creates 30 cm of net depth according to the familiar “volume divided by (height times width)” formula. All of the basses work with the same volume, which means that only one reflex opening is needed, measuring 4.2 x 19 cm at the front bottom. Three reinforcements stabilize the walls; four bags of Sonofil fill up the interior, and the lower 10 cm are kept open. We chose black-stained MDF as the building material, and the woman at the hardware-store register told us, “114 euros and 30 cents,” because it was once again time (after a good long while) to add a liter of joint glue to our purchase. We made the boxes look a little nicer with a shadow gap, which we created in just a few minutes using a special trimming router. We’d prefer not to talk about the fact that we accidentally nicked the lid of a box in the process, but our misstep is at least worth one tip: make sure you leave yourself plenty of time and plenty of room to move your arms, and take the first piece of wood off the table before you apply the merciless router to the second one. We filled in the nick with black repair wax later on and then re-cut it in the right spot. It took us much longer than simply moving the box onto the floor would have.
For anyone who has trouble deciphering the numbers here, the assembly plan is also available as Sketchup-file or a PDF.
If you want to operate four chassis elements with four ohms each in your boxes, you could connect them in parallel and hope that the amplifier has a functional protection circuit strong enough to protect them from a merciless death by overheating. A better option is to couple the chassis elements into a single unit by way of some clever wiring, which in turn creates a four-ohm load for the amp in the end. There are two possible versions: first, two pairs of chassis elements can be connected in parallel and then sequentially. Second, they can be connected sequentially in pairs and then in parallel. The first version is a good idea if all of the chassis elements will be operated in the same frequency range, which allows them to use a shared crossover. That’s manageable up to a separation at 400 Hz, but then who’s going to reproduce the mid-range?
In order to assign all four SB 17-4s to the basement level, as well as using two for the range up to the tweeter, the top and bottom chassis elements need to be connected to a shared crossover branch, which corresponds to the second version. That creates a two-and-a-half-way box in which the basses are only decoupled using one coil. You can see their positive influence on the interactions between the other two basses by looking at the red curve compared to the green one. It does not yet include any components, which creates strong dips at 1.8 and 3.6 kHz. The distance from each chassis to the microphone differs, which means that the phase descriptions do not match in these areas.
It was hard in any case to measure the SB 417 in my small 4 x 4 x 4 m room; the normal microphone distance is completely meaningless when there are five sound sources distributed over more than one meter of height. Therefore we had to go up to the limits of what could be measured and accept a few unattractive waves, which are particularly visible in the angle diagrams. For the upper bass mid-range speakers, without any consideration for the other members of the SB family (as we mentioned earlier), we built a third-order filter, which produced the blue curve. The high notes also created waves, which I didn’t need to worry about. The 12 dB filter created the green curve in the branch diagram. The resulting total curve reveals the cleanly crafted separation between the five chassis elements involved.
Since tube enthusiasts often prefer to use a box with 90 dB/ 1 m/ 2.83 V that is designed exclusively for listening to music (for precisely that reason), it was essential to measure out an impedance correction even though the peak of the separation frequency was only 9 ohms. It is shown with a dashed line in the circuit plan, since it will be used exclusively with tubes. The plan also shows you that all of the chassis elements are connected in phase.
The usual SB 417 measurement diagrams fit well here, some of which once again used our ATB. The distortion measurements, the step response and the waterfall just look nicer there, even if it is just a representation of the same material.
Measurement SB 417:
|Frequency response and phase||Impedance||Frequency response under 0/ 30/ 60°|
|Distortion for 90 dB||Step response||Waterfall|
All of these parallel and sequential maneuvers are probably making some of your heads spin at this point, which could lead to errors in assembling the SB 417. So we left more room for the installation phase this time and took a couple of explanatory photos. The associated texts can be read as captions by clicking on each image.
The listening report starts out in a somewhat unusual way this time. Two small pictures without much content, on differently colored backgrounds, give you a quick impression of how this change can shape your perception of the same object.
The colors on the black and white backgrounds are identical, and the font is the same size. Nonetheless, the bottom “ROT” (red) seems thicker, and the top “BLAU” (blue) seems lighter.
What does that have to do with loudspeakers, you rightfully ask. When it comes to listening, too, it’s also true that you need to have the same background in order to understand the description. When we talk about a contoured bass with good traceability, there’s no guarantee that our description matches up with what you are imagining. Only by listening to a pair of boxes together can we create a shared reference – aside from the fact that everything we hear is also evaluated subjectively. As a result, even the most euphoric list of every imaginable superlative can at best make us curious about the described object, make us want to hear it for ourselves. Whether enthusiasm or disappointment wins out in the end can usually only be determined after the speakers are built. We’re cat lovers, so we don’t like to keep the famous one in the bag – we encourage potential do-it-yourselfers to come in to our studio and listen to all of our suggested projects at length. That’s why you should consider the following sentences as an appetizer, the truth of which is (almost) always subject to your own findings.
We have already pointed out plenty of times in this report that the SB 417 is meant exclusively for stereo listening, so there was no trouble choosing the right amplifier for our test. We aren’t sticklers for principle, so you’ll never hear us say, “I only listen to tubes” or “I only use transistors.” Our goal is very modest: we want a signal transmitter that doesn’t set any premature limits. That can be said in good conscience about several KT 88 tube amplifiers, and the price is right too. So we hooked up the boxes, turned them on and started up the music. A little guitar-jangling from our last shopping excursion happened to be on the turntable and it was Friday night, so we let ourselves be teleported straight to San Francisco. It was breathtaking to hear how fast Paco de Lucia and Al Di Meola plucked the strings as they projected “Mediterranean Sundance” into the listening room in 3-D. The SB 417 didn’t complain a bit as it beautifully reproduced what felt like five hundred thousand individual notes with incredible dynamicism. Fortunately, when the recording was made in 1981, today’s standard compression approach hadn’t been popularized yet. After this demonstration of fundamental speed more or less in the mid-range, the almost 500 cm² of membrane surface – the same area as a #30 bass, but distributed across a meter of height here – showed how much fun it is to let your belly be massaged by high-pressure basses. Keith Emerson volunteered for that part, impressively using the organ at Royal Festival Hall on “Emerson, Lake and Palmer” for his progressive rock spiked with plenty of classical and jazz elements. Our familiar old listening couch rattled pretty nicely when he blew the air through the really big pipes for his impressive final chord.
Since we were already well on our way to classical music, Mahler was a must, given that May 18 was the 100th anniversary of his death. His Third Symphony, recorded 25 years ago by the Frankfurt Radio Symphony Orchestra with Eliahu Inbal conducting, left no doubts about the SB 417’s skills in this musical genre. The cymbals crashed, the kettledrum went straight for the gut, and the space and positioning of the instruments were perfect. There wasn’t a hint of scratchiness when we played Ravel’s Sonata for violin and cello. That is probably thanks to the tweeter, which at less than 40 euros manages to make some of its rivals for the listener’s affections look downright cheap. Overall, our design using the previously neglected SB 17-4 was more than satisfactory. Calling it a loser now will just make a liar of you in the next listening test.
Let us add a couple more sentences here to avoid the inevitable questions: the SB 417 fits seamlessly into the phalanx of SB boxes. It is a little more high-pressure and impressive than the SB 36 and not quite as deep as the SB 240, so it fills the gap between them both tonally and visually. At the same time, it can be independent, since we aren’t planning to make a matching center component out of the upper piece – but I’m sure we don’t have to point that out anymore by now.
|Chassis||4 x SB 17 NRXC-4||Wood list in 19 mm MDF, black, per box:|
|1 x SB 26 STAC-4|
|120,0 x 34,0 (2x) Sides|
|Sales||Intertechnik, Kerpen||19,0 x 34,0 (2x) Lid/Floor|
|Construction||Udo Wohlgemuth||19,0 x 116,2 (1x) Back wall|
|19,0 x 112,0 (1x) Front|
|Function principle||Bass-reflex||19,0 x 16.0 (1x) Reflex-board|
|Nominal imdedance||4 Ohm||19,0 x 10,0 (3x) Reinforcement board|
|Damping:||4 bags Sonofil|
|Terminal||K 30 AU pole clamps||Milling depth|
|Bass: 6 mm|
|Approx. cost per box:||
|Tweeter: 4 mm|
|Assembling kit:||360 EUR/USD||Wood cutting: 50 EUR/USD|
The SB 417 with SB Acoustics speakers is available from Intertechnik.