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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
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