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The new VAF DC-7 Generation 4 Kit Speakers This new speaker from VAF Research looks very similar to their highly regarded DC-X Generation IV but this model is smaller and much more affordable. It will fit more easily into smaller rooms but still offers a high level of accuracy and high sensitivity. By Philip Vafiardis & Simon Wilde 8  Silicon Chip siliconchip.com.au The 170mm black composite Kevlar woofers are specially made to VAF’s specifications. D Note the unusual vented voice coil & vented spider arrangement significantly reducing thermal compression and secondary resonance issues. id you admire and drool over the new Generation 4 version of VAF’s legendary DC-X loudspeaker presented in the August 2004 issue of SILICON CHIP? Maybe you liked the speakers but their imposing size and price presented some big hurdles. The new DC-7 G4 described here should be considered as a DC-X on a smaller scale. Still very accurate, with high sensitivity and low distortion, the DC-7 G4t is more compact and room friendly. In essence, the new VAF DC-7 G4t consists of two woofers, one tweeter and a slim floor -standing cabinet, in a design along the same general lines as the DC-X series. However, there is more to it than that. First of all the woofers and tweeters are far from ordinary. The 170mm diameter Black Composite Kevlar cone woofers have been specially made to VAF’s specifications. They feature T-shaped pole pieces and large, high-temperature voice coils. The spider and voice coil are also vented using the same method as in the larger woofers in the DC-X series. This provides dramatically improved voice coil cooling which significantly reduces thermally related compression. An additional benefit is that no air is trapped behind the voice coil. This motor structure offers exceptional dynamic linearity, providing a linear excursion of 7mm and a total excursion of over 12mm. The composite cone has been moulded using resins that provide exceptional damping. VAF then fit the cones with two proprietary pads to further enhance propagation of sound through the cone. The cone edge is terminated in a very compliant high loss soft rubber surround and specially treated with a proprietary decoupling ring. In addition, these drivers are magnetically shielded. Finding a single tweeter sensitive enough for the new DC-7 G4 but still being of very high quality proved to be a challenge. All the tweeters that were originally tested were Cumulative Spectral Decay of the DC-7 G4. Note how fast and even the initial decay is. The faster the speaker decays, the more easily a new sound it reproduces can be heard. The step response is almost ideal. The steep vertical rise indicates that the woofers and tweeter have good time alignment. siliconchip.com.au January 2005  9 Note the unusual heatsink fitted to the DC-7 G4 tweeter. The speaker connection terminals are capable of biamping: removing the straps between the pairs allows you to use separate amplifiers for bass and treble. either not sensitive enough or not accurate enough. The specified tweeter has a high temperature-resistant voice coil, rare-earth magnets, a 25mm treated silk diaphragm, a high-loss surround and Ferro-Fluid cooling for the voice coil. An integral shallow horn in front of the dome is carefully shaped to provide a flat overall response and efficient air-coupling. The tweeter is deeply recessed in the cabinet baffle to ensure time alignment. This ensures that signals from the tweeter and woofers reach the listener’s ears at precisely the same time. This is shown by the step response measurement which has an almost perfect vertical lead-in with a smooth return to reference level. This is a text-book result. The heavy cabinet also features angled bracing to minimise resonances in the panels and to act as reflectors to minimise the acoustic reflections inside the enclosure. In a normal cabinet this reflected energy eventually returns to the woofers and is radiated into the room. This is can mask the direct sound being reproduced by the woofers and can compromise fidelity. VAF have targeted Stored Energy in other ways too. As any tweeter radiates its sound forward it also radiates some of its sound across the baffle. If this sound reaches a cabinet edge it will be re-radiated and this will muddy the sound. These effects are combatted by the soft pads around the tweeter; these are highly efficient acoustic absorbers. They have two separate layers which have distinct individual shapes to effectively eliminate cabinet-related diffraction from the tweeter. A large quantity of VAF’s Hypersoft III Foam also fills the cabinet in critical areas, ensuring that internal reflections at higher frequencies are well attenuated. This is demonstrated by the very fast Cumulative Spectral Decay response. VAF believe that if acoustic problems are dealt with fundamentally and directly at their source, the resulting The Impulse response settles in under 0.4mS. Frequency Response of the DC-7 G4. Note how flat and smooth this response is even around the transition 3KHz to 8kHz crossover area. 10  Silicon Chip siliconchip.com.au A close up view of the tweeter area (centre of photo) showing the two individual layers of diffraction control. Specifications Frequency response... 43Hz–20kHz (1/3-octave smoothed) Phase response........... ±15° from 200Hz–20kHz Harmonic distortion.... 0.3% from 40Hz-20KHz at 93dB Nominal Impedance..... 8W (4W minimum) Sensitivity..................... 93dB/1W <at> 1m Dimensions.................. 1050 x 193 x 300mm (wxhxd) Weight........................... 36kg pair Standard finishes include Book Matched, Crown Cut Oak (as shown here) or Jarrah (as shown on page 8). Genuine Black Oak is also available. fidelity will be superior to the more normal design approach of using complex electrical crossovers to cover them up. This attention to detail enables the use of a far simpler crossover which even so, uses 1% tolerance resin-bound, air-cored inductors, close-tolerance polypropylene capacitors and non-inductive close-tolerance resistors. VAF supply the crossovers fully assembled with the labelled wiring loom already attached so assembly is very straightforward. The set of hardware supplied with the speaker kits goes as far as a spanner to do up the floor spikes! siliconchip.com.au Kit prices & how to buy VAF make these new speakers in three different forms. First, kits without cabinets: these include all the parts required to build a full pair of speakers but without the cabinets or cabinet materials. CAD drawings are provided for those who want to make the cabinets themselves. This is the lowest cost option at $799 per pair. A full kit including precision made, fully assembled and finished cabinets can be bought for just $1399 per pair. Standard finishes include book matched, crown cut oak, jarrah and genuine black oak. The DC-7 G4t loudspeakers can also be purchased bought fully assembled for $1599 pair in the same finishes. $42 fully insured freight applies to each kit option and covers most locations in Australia. Kits can only be purchased directly from VAF Research, Phone 1800 818 882 (free call) or fax 08 8363 9997. They are not available in shops. Email orders can be directed to vaf<at>vaf.com.au VAF make a wide variety of loudspeakers. See the full range at www.vaf.com.au SC January 2005  11