Like many people, I began my long journey to the SB240 with one of the smaller representatives of this magazine’s works: the SB18, which I then expanded into the SB36. I have been convinced for a while now that the SB series has the right sound for my musical tastes, so the move to the #240 was actually the logical solution for the increase in square meters in my new living room. But what scared me away from the #240 at first was the sheer size of the original assembly suggestion, which reminded me more of an overgrown cabinet than a speaker box. So in December I headed back to the listening studio; after all, the Vota and BlueNote are potentially smaller candidates. Plus I thought they were probably getting bored hanging around Intertechnik so soon before Christmas. ;-) After an extensive listening session with my sample CD, though, I realized what I had already known before: it simply had to be the SB240!
2 years earlier, while reading the magazine article about the SB240 for the first time, I ran across the following sentence:
two pieces would have suited our natural laziness if we had still had the SB 18 available for a demonstration. But whenever “if” and “but” are on the agenda, reality steps in and says, “no way!”“
No way? I immediately heard Barney Stinson’s voice in my ear: “Challenge accepted!”
With great foresight, I had spent my evenings with SketchUp and Excel weeks before the visit, and tested hundreds of drafts of the SB240. The result was a two-piece version that has a slightly wider footprint than the original draft, but appears much narrower because of the narrow tops and the wide 45° phases on the bass cabinet lids. The contrast between the black front and light side pieces makes the structure look even a little more “delicate.” In order to find space somewhere for the 100 liters of the two basses, there’s no way to avoid making a 1-meter-tall cabinet.
In order to still be able to enjoy my music sitting down, though, I decided to float the tweeters between the mid-range speakers and the woofers. The small indentation needed in the bass cabinet barely affects the volume, and the tweeter does not need any volume or damping. My structure also has a baffle board wide enough so that nothing needs to be built for the crossover. I was able to make the transition between the tops and the bass visually appealing by finishing the baffle board for the tops with a semicircle on the bottom, which shares its midpoint with the midpoint of the baffle board for the lower speakers. If the front width of the tops is set at 19 cm and there is a 1-cm-wide gap, the cutout in the woofer cabinet has exactly the same radius as the two woofers. The only thing missing from this draft is the bass reflex tube, which also needs to move to the front because of its position near the wall.
A day later, I went straight to the hardware store. As usual, my preferred hardware store cut the boards very precisely to size and did not miter them, since the boxes are constructed in a way that means no abutting edges are visible on the front. I spent my first week of vacation doing extensive work with the router, since I needed to use router templates and a trimming cutter for the front transition between the top and the bass. You can still use the router compass on the top section; but for the bass, the center of the circle would be one cm above the baffle board. As with all of my other projects, I cut out the baffle boards before I glued them together, which allows me to swap out any mistakes like the ones I immediately made with the tops.
The normal procedure for attached side walls is to make an MDF box and then glue on the side walls. Since I was already at the minimum with my volume calculation, though, the famous 10% wiggle room was no longer available. So I had to make cutouts in the side walls of my base box. With a material thickness of 19mm, that meant a good 8-liter difference for each box! If I were going to build it again, I would glue the whole box together first and then make the cutouts with a jigsaw. In my case, though, I cut them out first. The small contact surfaces for the side walls on the front and base made the gluing phase an exercise in patience, especially for the bottom part. That was just the moment for the Wolfcraft dowel tool, which makes drilling the right size dowel holes child’s play.
I didn’t document any more of the gluing process in pictures, since
a) it has already been shown very often and
b) I needed 6 of my 2 arms to hold it together.
I doubled the front in the overlap zone for the tweeter; I also decided to use 22-mm MDF for the front because of the larger cutout size for the woofers. The area where the tweeter would end up required another small overlap on the front, since another 4x10 cm of the second front panel would have to make way here. Since I plan to keep the SB240 for a while, I built magnets into the front for attaching speaker mesh later on – as protection against (as-yet unplanned) offspring. There are 8 magnets in the bass and 4 in each of the tops. I decided on round magnets with an 8-mm diameter, with a thickness of 8 and 4. The magnet strength test with 10-mm MDF boards confirmed that they were strong enough. Because of the large distance between the chassis and the chassis magnet, as well as the rapid decay of the magnetic fields as the distance increases, there is no need to worry about influencing the chassis.
Because of my wobbly glued structure, I had to do the initial sanding and puttying before attaching the side pieces. It’s a good idea to do a fit test with the chassis at this point too – the later you notice any problems, the harder it will be to fix them. ;) Fortunately, everything fit in my case. Measure twice, cut once! I also checked the later position of the crossovers. I built them on a piece of scrap wood; all of the components are attached with hot glue.
I assumed that the crossovers for the two woofers were the right size. If they hadn’t been, that would have meant I had made a terrible mistake in calculating the volume. ;-)
The next step was preparing the side pieces. As shown in the SketchUp draft, these would lie flush on the front and be slightly rounded off at the back. You can do this with a very large router compass, but my chosen radius of a good 4 meters was larger than the available room width. Here, too, I was able to use a template made of 10-mm MDF. First cut out the desired circle fairly precisely with a jigsaw, then use any sanding machine (in my case my girlfriend) to make it a true circle. Then use the jigsaw to roughly prepare the side pieces, and go over the circle shape with the trimming cutter. In order to make the transition of the side pieces to the back a little bit smoother, I sanded down the back edge fairly well. As a bonus, it gives you a nice effect with multiplex boards. I also checked the position of the side pieces before gluing them. The overhang on the top of the woofer cabinet will be removed later on.
When gluing on the side pieces, there was no way to avoid screw clamps. Fundamentally, the more the better, but not everyone has an endless supply of clamps. Fortunately I did have a helpful neighbor, so I had 5 clamps available for the tops and 7 for the lower sections. Even though there is a lot of strain here, two hours is plenty of time for the joint glue to dry.
The overhanging edges were then taken off with the trimming cutter. The multiplex side panels were also rounded off on the front edge, using a router with an 11-mm radius. That also makes the box a little narrower. While I went through a few cycles of puttying and sanding (I used pre-mixed Molto fine putty and was very pleased with its working properties), I started to think about how I would connect the top pieces.
I was advised against my original plan of adding a terminal to the underside of each top and one to the lid of the woofer in order to create a seamless connection; because of the short cable that was needed, it would be almost impossible to get to the terminals later. I eventually decided on pin plug boxes, which I set in almost flush using a 10-mm router.
I used bi-wiring terminals to connect the bass section. Bi-wiring is not part of the plan, but better to build it in now than be sorry later. Before I could move on to the final rough and fine sanding, though, the phases still had to be attached. I don’t happen to have a phase router with a cutting surface of about 5 cm, but I do have a circular saw with an adjustable cutting angle.
To help me cut straight, I screwed a guide board onto the bass sections and then puttied over the screw holes afterward. Then came another pre-sanding step with #60 grain (#80 would also have done it for the orbital sander) and an intermediate sanding step with #120 grain. I did all of the other finer sanding steps by hand, including the intermediate sanding with #180 grain.
Before I could launch into the painting phase, I had to take a short Easter break. I used the time to test the crossovers and break in the chassis.
The question of the color was relatively simple this time. Or so I thought. They were going to be black. And matte… to match the SB chassis. However, after extensive research I still hadn’t found a definite shade. Since the hardware store only has deep black in satin matte, though, which in my opinion doesn’t work well with the chassis color, my only choice was to go to a specialty paint store (with a mid-range chassis in my bag), where I received a very good consultation. That way I could be sure that the base, paint and clear varnish would all work together. I ended up with 1k water-based paints from Hesse, which can also be rolled on, and with the color RAL 7021, also known as black grey.
But first I followed the paint specialist’s instructions step by step. I started by taping off the side pieces with finely woven masking tape and film; after all, I didn’t want those to be black. #180 sandpaper was good for the base, then #240 intermediate sanding, another coat of primer and then, since I still had primer left over, a third coat. So now everything was white. I sanded it again with #240, then painted the back and added a coat of clear varnish; that way I had a surface to set them on and didn’t have to hang the monsters on the wall. After that, I painted the rest black (in 2 coats, including a careful intermediate sanding step with #240 sandpaper) and finally covered everything, including the multiplex sides, in a coat of clear varnish. Very important to remember while painting: be patient so the paint can dry well. I always let the base coat dry for a good 18 hours, and the paint and clear varnish overnight.
After installing the technology, I was finally convinced: RAL 7021 with a matte clear varnish finish was definitely the color I had planned on from the beginning. The connection between the lower sections and the tops, like all of the box connections, consists of 4 braided wire strands with a 1 mm² cross-section.
Still, the deciding feature of loudspeaker boxes is and always will be the sound… and it’s amazing. The SB240s, like all of the other members of the SB series, are extremely good at resolution and representing the stage. But what distinguishes them? Definitely their skill in the bass. Where the SB36 bowled me over already, the SB240 really jumps into the fray. In the words of Die Ärzte, “Immer mitten in die Fresse rein” (“always a punch right to the face” – even at low volumes. That’s exactly how I like to listen to my rock music. Because of the relatively small listening room (~25m²) and its position close to the wall, I filled up the bass reflex tubes with Sonofil. That makes the SB240 a bit calmer overall, especially when you have various genres in the mix on the radio, for instance – it’s the happy medium for my room. But if you need something really rocking, you can pull out the Sonofil in the blink of an eye. ;-) Incidentally, I run them with a small DIY Gain clone.
And why the SBs now? That’s easy: In various comparisons and listening sessions, they were the ones I liked best for most of my favorite songs.
You can order this assembly kit from Intertechnik