SB 417 loudspeaker kit – Two-and-a-half-way Floorstanding Speaker for Stereo Reproduction
Now that the SB 36 and the SB 240 are available, the question arises as to why there's a need for another bass-powerful version of the original SB 18 two-way speaker. For once, we didn't design the SB 417 with four 17 cm drivers for home cinema in the sense of the rest of the family, but tried to tickle the best possible out of this design for stereo reproduction.
Development
We got the idea to develop an SB 417 when we presented a 4-ohm version of the bass-midrange driver used in the SB 18: there was no use for the new SB 17 RNXC-4 within the existing home cinema family, as most newer AV receivers with their weak power supplies prefer to drive 8-ohm speakers. So this time we concentrated on the good old stereo days without regard to home cinema compatibility together with the other family members.Cabinet
Since we didn't want to invent an SB 18 with four ohms and an SB 36 already existed, the logical consequence was a design with 4 bass drivers per side. With 15 litres per bass driver, this results in a column of about 60 litres and 120 cm height, if the drivers are to be distributed properly across the front. The SB 417's cabinet depth, with 19 cm internal baffle dimensions, resulted in a net depth of 30 cm.Since all woofers should work on the same volume, a reflex port with 4.2 cm height and 19 cm depth was sufficient across the entire cabinet width at the lower cabinet edge. Three stiffeners stabilise the walls. 114.30 Euros was the price for the black MDF, including cut to size and joint glue, at the hardware store. Four bags of Sonofil filled the interior, leaving the lowest 10 cm free.
The boxes were embellished by means of a shadow joint, which was milled in a few minutes with a special flush milling cutter - the small carving caused by shaking made more work afterwards by repairing with repair wax than a calm, careful working method and a tidy workplace with sufficient armroom would have caused ...
Chassis
The distinctive basket with the narrow ribs and the raised collar immediately reveals to which loudspeaker family the SB17 NRXC-4 belongs. It simply has the same genes as the 8 Ohm version, how could it be otherwise? The smooth cardboard cone shimmers in grey-black and the dust dome of the same colour is similarly curved.
The thick lip, i.e. rubber surround, reveals a large diaphragm stroke and the voice coil with its 16mm high copper-coated aluminium winding on a glass fibre carrier, well ventilated thanks to the high centring spider and large holes, suggests an immense power handling. Its diameter is an immense 45.5 mm. The magnet with its huge 10 cm diameter is provided with a large pole core bore. The 16 mm winding and the 5 mm air gap result in a linear stroke of 11 mm. A copper ring on the pole core ensures low inductance and effectively reduces the degree of distortion.
Mid-bass drivers cannot make music on their own, only full-range drivers can, so the SB17 NRXC-4 needs adequate tweeter support. We chose the SB 26 STAC-4, which is practically identical to the SB18 tweeter except for the aluminium front and has not been used before.
Compared to the "A" model, it is a good 10 euros more expensive due to the metal front. The cheaper brother offers the same performance, but due to the popularity of the SB 18/ SB 36/ SB 240 it is constantly sold out and is also used in the Blues Box. So this time we have been unfaithful to our maxim of always choosing the cheaper product for the same sound quality, and for good reason. Why should the noble version of this tweeter gather dust in our warehouse? It will always look good in a noble hi-fi floorstanding speaker.
Frequency Switch
Four 4 Ohm drivers can neither all be connected in parallel nor all in series. The first case, with 1 Ohm, would result in a case for the hopefully existing amplifier protection circuit, which would put a stop to the strong currents; the second, with 16 Ohm, would call up too little power from the power amplifier. It is better to obtain a nominal impedance of 4 ohms again by means of a combined series/parallel circuit.
There are two ways of doing this: two speakers can be connected in parallel and then in series, or they can be connected in series and then in parallel in pairs. The first version is suitable if all drivers are to do the same work, the second type of connection is necessary if two of the drivers are to cover a different frequency range, as in our case, because otherwise we could only operate all four drivers together up to about 400 Hz and would need an additional midrange driver.
In order to assign the low frequency range to all four SB 17-4s, but also the midrange to two of them, the lower two and the upper two drivers have to have a common crossover path, which corresponds to the second variant. In this way, as with the SB 36, a two-and-a-half-way cabinet is created in which the woofers are decoupled by means of a coil. Their positive influence on the interaction with the other two basses is shown by the red curve in comparison to the green one. In the green curve, no components have been inserted yet, which leads to strong dips at 1.8 and 3.6 kHz - in the red curve, these two dips have been straightened out. The different distances of the drivers to the microphone lead to inappropriate phase relationships in the green curve.
Anyway, it was difficult to measure the SB 417 in a small room of 4 x 4 x 4 m, because the usual microphone distance fits for measuring a few drivers, but not for 5 sound sources distributed over more than one metre height. This explains the frequency response ripples, especially in the angle diagrams.
For the upper bass-midrange drivers - as announced without any consideration for the other members of the SB family - a third order filter was created that produced the blue curve, with a wavy high frequency response as well. Its 12dB filter produced the green curve in the branch diagram. The resulting cumulative curve reveals the neat separation of the five drivers involved in a quasi D'Appolito arrangement of the tweeter between the two upper bass-midrange drivers, which are the only ones radiating the midrange.
Since a loudspeaker designed exclusively for listening to music with a stereo system with a rather high efficiency of 90 dB/ 1 m/ 2.83 V also finds its fans among the operators of a tube amplifier, the dimensioning of an additional impedance correction was a compulsory exercise in this case - although the peak in the crossover frequency is only 9 ohms.
In the circuit diagram it is marked with a dashed line, as it is to be used exclusively in conjunction with tube amplifiers. In contrast to some other proposals of the SB family, in this case all drivers are connected in phase, which is also evident from the diagram.
Measurements
The usual measurement diagrams fit into this text position. For the SB 417 we have once again used the well-tried ATB. The distortion measurements, the step response and the waterfall diagram simply look nicer there, even if it is only a representation of the same facts.
Even if your head is spinning now: Please do not make any mistakes with the parallel and series connections! For clarification we have made an additional photo.
It is important to follow the assembly diagram that comes with the kit, as it explains which cable from the crossover has to be connected where.
Sound
When it comes to listening, the same background must be present in order to understand the description. If we write about contoured bass with good definition, this does not mean that you will hear exactly what we mean. Only when we have listened to the respective loudspeakers together is there a standard - apart from the fact that each listener then also evaluates or classifies what they hear subjectively. Thus, euphoric sound descriptions and superlatives can at best arouse curiosity about the loudspeakers described and arouse the desire to hear them for oneself or to copy them. Whether this results in disappointment or enthusiasm depends on many factors. In case of doubt, it is worthwhile to make a trip to Kerpen for a detailed test listening. After this little warning as an introduction, we can now give free rein to our enthusiasm about these speakers.
The SB 417 was designed as a pair of stereo speakers, so the possible choice of amplifiers is almost unlimited. Tubes or transistors, Class A, B or C, everyone has their preferences, the only important thing is that the power amplifier as a whole is suitable and provides enough power. For the sound test, we used a Destiny Experience with KT 88 and a decent price/performance ratio, so we plugged it in, switched it on and started the movie, no, the music - after all, it's not a home cinema box.
There was still a bit of guitar strumming on the turntable, and since it was Friday night, a musical trip to San Francisco was worthwhile. It was breathtaking to see the speed at which Paco de Lucia and Al di Meola tore into the strings when they projected "Mediterranian Sundance" in 3D into the listening room. The SB 417 reproduced what felt like five hundred thousand breaks of the individual guitar strings with incredible dynamics. In 1981, when the recording was made, fortunately not all music was recorded in compressed form.
Well, for slightly medium-heavy music it is perfectly suitable - and what about punchy basses? This part was willingly taken over by Keith Emerson, who impressively used the organ of the Royal Festival Hall on "Emerson, Lake and Palmer" for his progressive rock, peppered with many classical and jazz elements. It became clear that it's a good idea to distribute the 500 cm² cone area of a 30 cm woofer over four smaller drivers lined up on top of each other. The 417 played even the most powerful bass with tremendous speed and the imposing final chord made the room literally tremble with the moving air masses.
Since we were already moving in the classical genre with the previous disc, only with different musical tools, it was now time for real classical music. We decided on Mahler, whose 3rd Symphony was recorded 25 years ago by the Frankfurt Radio Symphony Orchestra with Eliahu Inbal on the podium. The SB 417 did not leave us in any doubt about its suitability for classical music: Brass rattled, the kettledrum attacked the belly, space and locality of the instruments fitted perfectly. And even the strings played without any scratchiness when Ravel's Sonata for Violin and Cello sounded. This is undoubtedly due to the tweeter, which at 40 Euros can be described as extremely affordable, relegating many a more expensive competitor to the back seat.