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Bowers & Wilkins CM-7 Floorstanding Speaker Review

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Bowers and Wilkins CM-7 floorstanding speakerIntro: Review a BMW? Sure! I thought I was branching out nicely when our editor called to inquire if I would like to undertake the review. However, it was my faulty hearing again, misinterpreting it as he said, “…review a B&W.” Ok, honestly, I knew immediately what he meant, but my mind fantasized for a moment that I could review speaker systems and high end imported vehicles! It seems the human mind has infinite capacity for greed and a voracious appetite for pleasing the senses. It’s probably a good thing that I have not been asked to test drive cars since it would likely ruin my vehicular contentment level! Audio has always been my big splurge, so much so that even if I were offered to be a car reviewer in place of audio reviewing, I’m not sure that I would take that offer.

It’s certainly not a letdown in terms of quality to review a B&W speaker. Known practically the audiophile world over, Bowers and Wilkins have made many a discriminating listener happy. Priding themselves on a reputation of quality two-channel speakers, they have incorporated some of their most successful technologies into an affordable crossover (two channel/HT) line called the CM series, for “Compact Monitor.” I had a chance to get some insight on the three-way CM7 from Mike Gough, Director of Project Development for B&W, who indicated that the target user for the CM line is the consumer who wants B&W’s sound quality in a more traditional wood cabinet without the top-mounted tweeter.

“Due to the compactness of the drivers near the top, it stands as a perfect case for the argument that in an application where a stand is used with a monitor, it should be replaced with a floor stander to yield superior sound.”

The CM7 in some ways is less a tower speaker than an “extended bookshelf monitor” in a tall cabinet. With a petite footprint, thin profile and the mid and tweet colliding in the upper quadrant of the cabinet, it looks and behaves in a very monitor-like way. Due to the compactness of the drivers near the top, it stands as a perfect case for the argument that in an application where a stand is used with a monitor, it should be replaced with a floor stander to yield superior sound. Having used various configurations on sub/monitor speaker systems in the past in smaller spaces, I have spent quite a bit of time attempting to make monitors and subs yield the full sound of towers. In so many instances it’s a chimera, a dream. Often one is better off to simply get the tower speaker that takes up the same footprint as a stand. Can a mixed sub/monitor system outshine a floor standing pair? Sure, there are likely dozens of examples, BUT do you have the time, money or energy to try them all? If not, then likely you should stick with the same family of speakers for the system or you’ll be asking for trouble integrating them. In most cases, your best bet just may be putting the small tower in the rig.

Regarding WAF, every time my wife has complained about floor standing speakers, it has been over the height or width. There seems to be a natural boundary which women sense in regards to size of speakers in an environment. If the floor stander encroaches upon it, there is an outcry. Keeping the overall dimensions of the tower within the parameters of a monitor and stand can allow one to simplify, and quite possibly, improve the system overall. And, who knows? You may even get to keep using the subwoofer!

The Bling-Factor

B&W is walking a tightrope with the sound and the aesthetics of the CM7. They are looking to preserve their tradition of luxury, yet at the same time appeal to trendy HT décor devotees. The bling-factor is ratcheted up substantially by the involvement of brushed metal rings surrounding the drivers. The wide tweeter ring reminds me vaguely of a compact disc glued to the fascia of the speaker. Flashy? Yes. Classy? Less so, but remember, these are not speakers with pretense to residing in the finest rooms in Europe and America. They are middle class speakers that are fun and meant to be dropped (or should I say placed?) into functional multimedia environments, without embarrassing themselves when called upon to perform serious two-channel duties.

“The CM7 stays just under the gaudiness level; while demanding one’s attention, it does not give cause for dismissal as a cheesy speaker.”

A further comment regarding “bling-factor” and components. Audiophiles at times seem excitable for anything novel and exquisite looking. Glowing blue lights under an acrylic base, speaker cabinets machined from a block of aluminum – the amusements never end but don’t come close to ensuring said product will sound half-way decent. I’m guessing B&W is feeling the pressure to develop more exciting speaker cabinets to snare younger customers. Why not, as long as they don’t go over the line? The CM7 is near the line, but not over. Chrome-like finishes seem to be all the rage lately, with car manufacturers also adding prodigious amounts of faux chrome finishes to interiors. Sometimes it’s so overdone it becomes nauseating. I was given a Chrysler Sebring as a rental a few weeks ago, and the amount of trashy silver trim was atrocious. The CM7 stays just under the gaudiness level; while demanding one’s attention, it does not give cause for dismissal as a cheesy speaker. Hearing them, likewise, piques one’s curiosity as they aspire to the sound of higher-end speakers.

The CM7 has the kind of sound I’d like to hear with a 15” bass, 6” mid and 2” treble. Wait, maybe that’s the model 801!

B&W has scaled down the success of their premier line and placed a prodigious amount of that technology into the CM speakers, including a Kevlar FST mid driver, “Flowport” technology and the famous Nautilus Tapering Tube for the tweeter. With all this inherited technology from its larger siblings, the CM7 should sound good, and it does! One could say that B&W has done a “headhunter’s job” on the speaker, turning one of the big boys into a physically shrunken speaker but with the soul intact.
As I encountered the speakers, the build quality, as becomes a B&W product, was faultless – not one iota of inferiority even though this was a mid- to lower-price product from B&W. It was evident that pride of craftsmanship runs deep in this British company. Well noted were the stickers on the shipping boxes proclaiming, “The Queen’s Award for Enterprise Innovation 2005.” Even B&W’s more modest offerings are not going to be brushed aside as tawdry. In finishing off the smooth Nutmeg hued cabinet, sensibility was employed by the use of magnetized grill covers – a nice touch for the customer straddling the two channel/HT line.

In hooking up the CM7, it seemed initially that spades of any size less than the gargantuan kinds would not fit on the binding posts. With the posts tucked into the contour of the speaker and at the bottom of the cabinet, my 3/8” MIT cables didn’t seem to fit, and it was difficult to see what was happening. I tried to insert one prong into the hole mid-post and cinch down as well as I could, only to find out later from Mike Gough at B&W that the unusual loose ring (or if you can visualize it better, a collar) on each post can slide up or down to reveal a tapered post, which can accommodate as small as ¼” spades. Looking back it was quite the humorous situation; as I was working blindly to attach the posts at the bottom of the speaker cabinet, there was one time I thought I really had those spades tight! Later on, after cycling speakers, I just couldn’t get them that way again. Obviously, I had the collar in the right position at one point and the spades locked down properly. Without mention of this feature in the manual it was a mystery. Prior to Mike clarifying the use of the post, I was going to recommend people avoid spades with the speaker; but having learned of the varying diameter “post and collar” system, I’m tempted to think that it’s clever.

Technologies

The CM7 induces excitement in listening, mainly due to the vibrancy of the FST mid and accuracy of the tweeter. It’s a “party ready to happen” speaker, not a laid back “your grandfather’s” type of speaker. One of my initial impressions borne out consistently as I reviewed them was that these speakers party with solid state, but sing with tubes.
The Kevlar mid imbued with FST technology and the Nautilus Tapering Tube are what I would consider the hallmark technologies of B&W. The FST, for “Fixed Suspension Transducer”, on casual observation appears to be a misnomer as the cone is not fixed – there actually is a surround – it’s just shrunk to a near vanishing point. In appearance, it seems the foam surround is made to be so small that it can not extend to any, ahem, extent. To my mind, it seems that there has to be something absorbing the excursion of the cone, or else distortions will result from the harsh contact point between the cone and cabinet.

Kevlar FST midrange driver in Nautilus
Mike from B&W shared insight regarding the FST:

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“Surrounds that are flexible enough to allow the cone to move sufficiently and with good dynamics at bass frequencies don’t always give the best response in the midrange. In extreme cases you can get the surround moving in the opposite direction to the cone, which gives a pronounced dip in response.”

I asked Mike if the FST system could be faulted for the same limitations of planar speakers, that is, a rigid mounting to the cabinet limiting the excursion of the drivers. He replied, “That would be a valid criticism if the driver had to produce bass notes as well. Seeing as it doesn’t, the required excursion is remarkably small.” Translation: The mid driver is virtually sitting still anyway compared to the bass driver, so shrinking the surround doesn’t have an adverse affect. Complementing this limited excursion arrangement, the FST’s magnet structure and chassis are minimized to allow the utmost air flow behind the driver. While there may be other speaker manufacturers or audiophiles who vehemently disagree with Mike’s conclusion or the B&W design, to my ear B&W seems to have produced a competent-sounding midrange using this technology.

Tapering Tube tweeter in the Nautilus

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Regarding the Nautilus Tapering Tube, this is the type of technology that can spawn fights between engineers. I have deep familiarity with the Von Schweikert VR-4 SR MkII speakers, which incorporate a rear firing driver to use the reflective boundaries of the room in the recreation of the original listening experience. The reflective waves add to spaciousness in the presentation. Obviously, B&W is not going to subscribe to that logic! Rather, it seems they want to eliminate all non-primary wave launch tweeter activity. It’s a behind the scenes (behind the baffle) “black hole” approach, where if it doesn’t come directly at you, its not going to come at you! It seems this is a silent renunciation of any design using a tweeter in a traditional cabinet, or at least a suggestion that they are inferior. No wonder this tapered tube is trickling down through the line of B&W speakers.

‘“Tapering the tube enables you to make it shorter for the same level of absorption. It acts like a horn in reverse …”’

B&W Flowport

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My caveat with this technology is that it sounds suspiciously like a miniaturized sealed cabinet design; if the tube is sealed (and I’m not sure it’s 100% sealed), then the vacuum could in theory affect the tweeter’s excursion. Maybe it is negligible in tweeters, but it appears the technology has been employed in B&W’s larger speakers as well, most notably the namesake Nautilus. It is possible that this limited excursion is hinted at on the B&W website where it states, “Tapering the tube enables you to make it shorter for the same level of absorption. It acts like a horn in reverse – reducing the sound level instead of increasing it,” and, “To maintain the effectiveness of tube loading, you must restrict the bandwidth of each driver. This is one reason why the Nautilus loudspeaker is divided into a 4-way system.” If the drivers are not as free to move with sealed enclosures, then logically they would need to “specialize” in certain frequencies, or have limited bandwidth.

Mike confirmed my suspicion that the tweeter’s Nautilus Tube is indeed sealed:

“When the tweeter is on top, in most instances the back end is open. There is therefore no air pressure spring. You can’t have this though when the tweeter is in the main speaker cabinet, otherwise the motion of the co-existing cone driver would modulate the tweeter dome and add distortion.”

For this reason the back end of the Nautilus Tube is sealed in the CM7. While reassuring that the “spring stiffness” resultant from the sealing of the chamber is nominal due to the size of the chamber, he seemed to confirm my hunch that each driver specialized in a certain frequency range, indicating, “A normal tweeter with no added cavity of any kind behind the dome would show a higher fundamental resonance frequency.”

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