Bowers & Wilkins manual Pretty sharp, Cone edge, Product B&W CM7

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

As 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.

REPRINTED FROM november 2006