CDM models 1 and 2 - the initials stand for Compact Digital Monitor - are completely new designs, not reworkings of past successes, although they both make use of established B&W philosophy with their Kevlar cones and light alloy dome tweeters. Indeed, while the CDM 1 cabinet is slightly larger than CDM 2 and has the added complication of a sloped upper section in winch sits the external time-aligned tweeter, the unit complement is almost identical. I have been listening to both of these loudspeakers for some weeks now and am making a calculated move in choosing to report on CDM 2, the smaller and less expensive of the two, because, although those two factors just described have their own influence, its traditional box shape is likely to have a wider appeal.
Whilst the CDM 1 retains the traditional 165mm outside diameter die-cast chassis for its bass/midrange driver, for reasons of economy the CDM 2 uses a bought-in pressed steel basket. I believe this to be the initial appearance of such an animal in a B&W-produced driver. However, both versions use identical 120mm diameter Kevlar curved cones suspended on moulded convex rubber surrounds; a central soft-domed dust cap conceals the 31mm diameter voice-coil, wound on a high temperature resistant Kapton former, which in the case of the B&W CDM 2 had a DC resistance of 5.2 ohms. The usual ceramic based magnet assembly is used and the pole and voice-coil proportions are arranged to permit a reasonably linear long throw.
The tweeter is yet another flavor of B&W’s well regarded metal dome unit in its ceramic magnet version with magnetic fluid in the gap and a coil measuring 4.5 ohms. Although the bass/midrange is rebated into the front cabinet wall- and carries a neat trim ring to conceal the fixings, for some obscure reason the tweeter is fitted within a huge ugly ribbed flange, glaringly offset and retained by no less than seven assorted projecting hex-headed bolts and screws - a good and sufficient reason for operating with the grille covers in place.
The major areas of the cabinet are constructed from 18mm thick MDF, one exception being the front baffle which is 20mm thick to accommodate the main unit and to provide a radiused edge to minimize diffraction; a similar but lesser radiused contour occurs at the rear around the slightly recessed rear panel which is finished in black. All other surfaces apart from these edges, which carry a matching satin lacquer, are veneered in ash and this is then stained in the inevitable black or an alternative attractive dark red. The previously mentioned grille is a cleverly shaped plastics moulding some 20mm deep and covered in black stretched fabric; its effect on the sound is (fortunately) virtually undetectable.
Internally there is one figure-of-eight horizontal partition cut from 20mm particle board and the four sides are covered with sheets of acoustic foam. The rear panel has a flared tunnel port above partition level, 125mm long by 30mm diameter. A removable acoustic resistance foam bung is provided which gives the user some control over the bass performance. Lower down is a large recessed four-terminal connection panel. The sturdy terminals are gold-plated, have 4mm centers and will accept very stout cables; there are also gold-plated link plates for single wiring. The crossover behind this panel is quite simple: a single 1.7mH cored inductor is connected in series with the bass/midrange and a ‘T’ section filter plus an attenuating resistor feeds the tweeter.
Measurements revealed what the initial listening tests had suggested; the CDM 2 has a remarkably flat frequency response, particularly over the important midrange where the ear is most sensitive and extending right up to the limits of hearing at 20kHz. Low frequency performance is of course very dependent on room position and dimensions but B&W have added to the variables with the optional resistive foam bung inserted in the rear port.
The effect or this is perhaps best appreciated by the way it changes the impedance curve. The free-air resonance of the bass/midrange driver is 32Hz; installed in the box with the port unobstructed reveals the normal twin bandpass peaks at 15 and 80Hz and this is probably the configuration the majority of users would find most acceptable. Inserting the loam removes the bandpass effect, the behaviour becoming that of a closed box with a controlled leak, exhibiting a single flatfish resonance centered on 73Hz. This mode of operation is better for ‘boomy’ rooms, often those with more nearly square or cubical dimensions, and can then provide a more acceptable bass extension than would otherwise be the case (closed box systems fall away at frequencies below resonance more slowly than band-pass systems).
Lastly of course, as with all ported systems, it is possible to close the port altogether which in this case will sharpen up the 73Hz resonance, raising output in this area by some 6dB which might be a popular mode for pop music enthusiasts. Which is ‘right’? The only true answer can be whichever sounds best on the most varied material.
Performance
Installed on heavy 450mm (18 in) stands in my usual listening room it was readily possible using the open port condition to decide on an optimum placement which satisfied the main criteria of an even and reasonably adequate bass allied to a realistic sound stage. I had already decided from initial tests that this was a very good loudspeaker indeed and over the next few weeks the B&W CDM 2 did nothing to alter that verdict. It so happened that they took the place of my pair of original Quad electrostatics, which I periodically use for a few days as a way of purging my hearing of any developed prejudices, and I was pleased to note the marked similarities in transient behavior-usually the biggest let-down on returning to moving-coil loudspeakers.
The pianoforte as always is a leading demonstrator of such deficiencies. Many years ago-well it could have been six or seven - someone had given me a digitally remastered recital by jazz pianist Erroll Garner taken from mono tapes made around 1950 (CD CBS 4606142). I recall sampling it at the time on now forgotten loudspeakers and, unimpressed, shelving it where it lay untouched until a browsing visitor pulled it out to be played on the CDM 2s. I may say that we were both most agreeably surprised by what they made of it and it has now been returned to a more prominent spot in my collection.
And so it was with a wide range of programmed material: “even handed and competent” makes for a mundane description or this loudspeaker's merits but it is an accurate one. The B&W CDM 2 has no time for fanciful excesses or imposed coloration, preferring to deal honestly and accurately with the signals fed to it. It joins the bare handful of small and smallish loudspeakers which I could happily live with if the occasion demanded.