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Big, bold & beautiful . . . VAF’s 2-Way To Want to build a pair of speakers which are big, bold and beautiful and won’t cost a fortune? Have a look at this tower speaker from VAF Research. It comes with fully assembled cabinets and virtually all you have to do is install the speakers and some hardware. By LEO SIMPSON Each speaker system uses two woofers and a horn-loaded dome tweeter. Other items in the loudspeaker kit include the pre-wired rear connector panel, felt damping pieces to go around the tweeter and foam-backed adhesive tape for sealing around the woofers and the base panel. Standing tall – the VAF DC-X tower speaker with the grille cloth frame removed. The big advantage of a tower speaker is that you get a big enclosure which takes up little floor space. 54  Silicon Chip www.siliconchip.com.au and they sound great ower Speakers N OW WE HAVE already said that these speakers are big, bold and beautiful so if you are looking to build a pair of petite speakers to go on a bookshelf, these are not the ones for you. If you need to clear this purchase with your partner, tell her/him that they would be great as the front speakers in a top-quality home theatre system. And you can have them finished in real Cherry wood veneer rather than boring black. Did we say they are big? Well they are quite tall at 1245mm but they don’t take up much floor space – just 268mm wide by 306mm deep. In fact, there are plenty of much smaller speakers on stands that would take up more floor space but they won’t have the punch of this system. In fact, this is the big advantage of a tower system; you get a big system but it does not take up any more floor space than a much smaller system. No special tools are required to put the systems together. You will need a drill, hammer, screwdriver, soldering iron, sharp utility knife and not much else. When you have put them together, you will have a pair of speakers which look really good, with up-tothe-minute styling. They come with black finished top and bottom plates and a full width grille cloth frame which makes a nice contrast with the Cherry veneer side panels. Actually, there are several models available. One with a stained black cabinet and wraparound grille cloth which slips over the cabinet like a sock and the other which comes in Cherry veneer. We assembled the Cherry version and in our opinion it is by far the more attractive of the two. There is no assembly required for the cabinets themselves and that saves a heap of work. Nor do you have to worry whether your workmanship is up to par since the cabinets are of the same standard as that for finished systems on your hifi retailer’s floor. To help make the whole assembly process easier, we have taken a series of photos showing most of the steps required. While it does take some time, we reckon you could assemble one speaker in an evening, so after two nights you could be listening to fine music. By the way, while the cabinets appear as simple towers, their internal structure is quite complex, with internal compart­ments and bracing. So they would not be simple to put together if you had a wish to assemble the cabinets yourself. Drivers and crossover Two 200mm (nominally 8 inches) woofers and a single horn-loaded dome tweeter make up the speaker complement in each cabi­ net. The www.siliconchip.com.au The tweeter is mounted on a recessed panel in the front baffle and then is surrounded with zig-zag shaped pieces of thick felt to damp any peaks in the response due to the cavity. woofers are quite unusual in appearance. Instead of the common black polycarbonate cone, these have a woven yellow com­ posite fibreglass cone and black neoprene rubber roll surround. Four pieces of blue felt have been glued to the cones, presumably to damp unwanted cone resonances or modes of vibration. The woofers, which are made in France, are fitted with a large ceramic magnet and have an edge-wound voice coil with a diameter of about 42mm –quite large. The effective cone diameter of the woofers is 150mm, giving a total February 2002  55 Cost And Availability Fig.1: the on-axis frequency response is within ±2dB from 35Hz to 20kHz. Fig.2: the on-axis phase response is exceptionally flat. Fig.3: the impedance curve shows a minimum of 4Ω between 100Hz & 1kHz. Note the characteristic “double-hump” at the bass end; typical of a bass reflex system. effective bass cone area for the DC-X system of 353cm2. The tweeter is also interesting, being a horn-loaded soft dome type and fitted with a large ceramic magnet. It is mounted in a recess in the front baffle to give “time alignment” with the woofers. This recess is heavily damped with zig-zag pieces of thick felt to prevent any nasty peaks. With all the cone treatment applied to the woofer, it apparently has quite an attenuated high frequency response be­ cause the DC-X manages with a very simple crossover network. The parallel-connected woofers are fed with the full frequency range from the amplifier while the tweeter is fed via a 3.3µF capacitor and 0.47Ω 5W wire­ wound resistor. These components are supplied already mounted on the inside of the rear connector panel so there is no extra work to be done with 56  Silicon Chip regard to that aspect. Note that the rear connector panel features two pairs of heavy duty gold-plated binding post terminals and these are normally strapped together. By removing the gold-plated straps, you could “bi-amp” the DC-X systems (ie, use separate amplifiers for the woofer and tweeter) but we would not bother. Regardless of the simplicity of the crossover network, the claimed frequency response is commendably flat, being within ±2dB from 35Hz to 20kHz and with useful output down to below 30Hz. See Fig.1. Moreover, the phase response is very flat, with a claimed ±5° between 100Hz and 20kHz (see Fig.2); that is the big advantage of using a really simple cross­over network. The impedance curve is shown in Fig.3 and nominal impedance is stat- As built, with MDF cabinets in Cherry veneer, the VAF Re­search DC-X speakers are priced at $1399 a pair. You can check the VAF website at www.vaf.com.au to see all the various price permutations. You can also get the speakers fully assembled for an extra $330 a pair and for many people, that will be regarded as a good option, in spite of the fact that the assembly process is quite straightforward, as we shall see. The DC-Xs come with detailed assembly instructions which are quite easy to follow. The following series of photos shows most, but not all, the major steps. The cabinets arrive separate­ly packed and have some of the foam filling already in place. As well, you will receive a box with all the drivers, the rear socket panels with crossover network and speaker leads already soldered, and various other pieces of hardware, grille cloth, etc. ed to be 6Ω although for a significant portion of the frequency spectrum between 100Hz and 1kHz, the impedance is around 4Ω. Interestingly, VAF Research describe the model DC-X as having cabinets which are a “unique tapered lossy line design”. OK, so what about the bass port on the front baffle? Doesn’t that make it a bass reflex? Well, yes and that is supported by a glance at the “double hump” of the impedance curve at bass fre­quencies. But apparently the tapered chambers inside the enclosure, which are packed with a variety of foam damping materials, do pretty heavily damp the output from the rear of the speaker cones and so too, the port. By the way, rated efficiency of 95dB/ watt at one metre is very high and it means that the DC-X loudspeakers will give a very good account of themselves with a relatively small power amplifier in smaller rooms. Recommended amplifier power is from 10-200W RMS per channel and presumably that applies to normal program material (ie, not continuous tones). With a 100W (or high power) per channel amplifier, you can rest assured that the VAF Research DC-X speakers will produce a wonderfully smooth response on all types of music, particularly classical and jazz. They should give many years of sound satis­faction. www.siliconchip.com.au STEP 1: turn the tower enclosure upside down and insert two wedgeshaped pieces of foam into the bottom compartment. The pieces fit against each side of the cabinet, leaving a large free area in the middle. Three other foam sections need to be inserted if the cabinets do not already have it fitted. STEP 2: fit the rear connector plate. Place the enclosure face down and pass the wires attached to the terminal plate through the hole in the rear of the cabinet, through the hole in the internal brace, to one side of the port tube and towards the front of the cabi­net. STEP 4: turn the cabinet face up and pull the labelled speaker wires through the respective holes in the front baffle. STEP 3: position the terminal plate in the hole, drill four pilot holes for the mounting screws and screw the terminal plate into place. www.siliconchip.com.au STEP 5: Fitting the woofers: first, apply the black foambacked tape around the holes for the woofers. This is to seal around the woofer frames when they are screwed down. February 2002  57 Step 6: solder the labelled wires to the terminals of the woofers. Do not solder directly to the terminals of the tweeter as it is too easy to damage them. Instead, we fitted some crimped quick-connects to the tweeter wires and then just pushed them on. Be sure to double check the polarity of all connections. Step 7: fitting the felt pads: there are number of zigzag-shaped felt pads to go around the tweeter. These are glued in place to stop them from becoming dislodged. Step 10: install the cap clips into the front baffle – these allow the grille cloth frame to be clipped on the baffle. Step 8: fitting the grille cloth Lay the two grille cloth frames face down on the grille cloth and cut it in half. You then fold the grille cloth over one of the frames and then secure it by pushing the supplied black plastic spline into the pre-cut channels. This job is made easier if you use a spline tool intended for use in making flyscreens. Step 9: after the splines are all in place, trim the material all round with a sharp utility tool. 58  Silicon Chip Step 11: installing the base & top: run foam tape all around the bottom cutout to seal it when the base panel is installed; then drill the holes for the base retaining screws and screw them home. www.siliconchip.com.au Step 12: the top panel is installed with the same cup clips as used for the grille cloth frame. Step 13: the last step is to peel the adhesive backing from the VAF badges and position them on the grille cloth. Right: the finished VAF DC-X tower speaker pair, with and without the grille cloth frame. The finished speakers really do look impressive. UM66 SERIES TO-92 SOUND GENERATOR. THESE LOW COST IC’S ARE USED IN MANY TOYS, DOORBELLS AND NOVELTY APPLICATIONS 1-9 $1.10 10-24 $0.99 25+ $0.88 EACH INC GST www.siliconchip.com.au February 2002  59