A
s the world leader in hi-fi
loudspeakers, Worthing-based
B&W has been particularly
adept at finding and/or creating
niche-filling models at a wide variety
of prices. The company has a dozen
different series of models covering
every conceivable price, size and
style. The CM-series models are
relatively recent arrivals on the scene,
initially filling a gap between the
vinyl-covered, budget-price
600-series and a more stylish and
technically advanced CDM-NT Series,
essentially by combining the
engineering of the former with the
real-wood veneer of the latter.
Recently though, things have
become rather more complicated.
The mid-price CDM-NTs are no more,
replaced by the 700-series and a
wholly new slimline metal-jacket
XT-series launched at around the
same price. The two new latest
introductions from B&W are in this
intermediary CM-series; both sit in
the gap between the 600s and the
700/XTs, but they’re rather more
than just prettied up 600s. They do
have the attractive real wood finish,
but they also borrow some of
technologies from the 700/XTs.
This was not particularly evident in
the little two-way CM1 miniature,
which we reviewed in HFC 277 and
HFC 279, but it’s far more obvious in
this three-way floorstanding CM7.
Although its £999 per pair price tag
is substantial, this is also the first
time that the company’s radical FST
midrange driver has been available at
such a low price. This unique feature
demands proper explanation.
The FST (Fixed Suspension Transducer)
is a special type of midrange driver, which
B&W engineers originally pioneered in the
much more upmarket Nautilus models. Its
particular distinguishing factor is its
replacement of the usual type of flexible
surround attached to the edge of the cone
diaphragm by a polymer ring. This ring is in
contact with, but not physically attached to,
the cone edge.
The logic is impeccable. In the majority of
three-way designs, the midrange driver is either
the same as (or a scaled down version of) a
bass driver. But the difference between a
midrange-only drive unit and a driver required
to produce bass (with or without midrange) is
that a bass unit needs to allow significant
fore’n’aft excursion, and this factor is quite
unnecessary in a midrange-only driver.
Whereas the multiple roles of the
conventional rubber roll surround include
centering the cone, absorbing edge-of-cone
vibratio and permitting
generous fore’n’aft excursion, by
omitting the last of these, B&W
engineers have designed a cone
termination specifically oriented
towards optimising the vibration
absorption characteristics, by
using a heavy rubber gasket in
place of the usual roll. The
alleged consequence is a
significant improvement in
dynamic range resolution.
The attractive sharp-edged
cabinet, made in B&W’s Danish
factory, comes finished in
wenge, rosenut or maple
real-wood veneers. Our rosenut
samples lacked any real grain
and therefore weren’t the most
convincing, it must be said (but
then neither is the concept of a
rosenut tree). But the end result
is at least marginally preferable
to vinyl woodprint.
To avoid lugs, magnets hidden
beneath the veneer hold the
fabric grille in place, and all
three drivers are flush-mounted.
Matching the shiny trim around
the other two units, the
tweeter’s highly polished
faceplate is partly cut away to
allow it to be located as close to
the midrange unit as possible.
The tweeter is fitted
conventionally into the front of
the enclosure, not externally
which is B&W’s favoured
approach, but it does use an
internal Nautilus-style rear
loading tube. The 25mm alloy
dome gives output right up to 50kHz and
also has a low enough resonance to allow a
first-order, single capacitor network.
Pretty sharp
Sharply styled and classily finished, the CM7 introduces B&W’s unique FST driver at a new low price
PRODUCT B&W CM7
TYPE Floorstanding loudspeaker
PRICE £999 per pair
KEY FEATURES Size (WxHxD): 20x91x30cm
P
Weight: 20kg
P
25mm aluminium dome tweeter
P
130mm ‘surroundless’ FST Kevlar cone midrange
driver
P
165mm paper/Kevlar cone bass driver
P
Sensitivity: 88dB
P
Impedance: 8 ohm (nominal)
CONTACT
01903 221500 q www.bwspeakers.com
REPRINTED FROM november 2006
HFC286.bw 56 19/9/06 11:12:13
(12 pages)
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