Doug Schroeder examines the viability of trickle-down technology in the B&W CM-7 loudspeaker
October, 2007
SPECIFICATIONS:
MSRP: $1,800/pr
MANUFACTURER: Bowers & Wilkins B&W Group Ltd Dale Road Worthing, West Sussex BN11 2BH
Tel. +44 (01903) 221 500
URL: http://www.bowers-wilkins.com Email: uksales@bwgroup.com
B&W Group North America 54 Concord Street North Reading, MA 01864
Tel. (978) 664-2870
Email: marketing@bwgroupusa.com
Intro: 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: “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
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 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.” I suspected that the result of the FST mid and the sealed tweeter enclosure would mean a speaker with less sensitivity, but I was not prepared for just how low it would be. The manual pegs the sensitivity of the CM7 at a fairly low 88dB. This is pushing towards the low end of the sensitivity scale, where the scale runs from about 101+ on the top-end and to 80 on the abysmal-end. The Eminent Technology LFT-8B at 83dB takes a lot of juice to sing loudly! At 88dB the CM7 is down lower to the Magnepan 1.6’s at 88dB than many dynamic speakers. Though the variance in numbers seems small, the effect is pronounced; the Von Schweikert VR-4 SR MKII at 92dB, on the other hand, is easy to drive. Consider this; with each 3dB increase in sensitivity in a speaker, the amplifier needs only half the power to produce a given volume! It also works in reverse, as a 3dB decrease in sensitivity calls for a doubling of power to reach the same volume! Consequently, with inadequate power the CM7’s may not live up to their potential. I can certainly see an audiophile scratching his head in wonderment as he arrives home and hears the B&W’s hooked up to his surround receiver, “Why don’t they sound ‘gripping’ like they did on the big system at the HiFi shop?” Indeed, he has answered his own question when he chose the word “big,” as in big power. I suggest B&W owners with lower-sensitivity speakers investigate their amplification and see if they’re starving their speakers for power. If the sound has not been satisfactory, that may be the primary reason. When I proposed to Mike that the CM7’s might be low in sensitivity, his response was, “We wouldn’t necessarily consider 88dB particularly low. Like all passive speakers, we are bound by the relationship between box size, efficiency and bandwidth (i.e. bass extension). If we wanted higher efficiency, either the box would have to grow or we’d get less bass. The one advantage in sacrificing efficiency is that, to some extent, you can recover the maximum sound level by making the speaker handle more power.” It is a very good thing, then, that B&W did not lower the sensitivity further, since the speaker is rated at 62 Hz +/- 2dB on the low end. If your old speakers were higher sensitivity and you move to the B&W’s, you may feel you’re “missing something,” because you have to crank up the volume more. If so, it’s time to investigate a new power source. Once done, these speakers will wake up nicely. I heard this effect precisely transitioning from those sweet little numbers, the Monarchy Audio SM-70 Pro mono blocks, to the twin Pathos Classic One MkII integrateds bridged at 170 wpc (270wpc at 8 ohms!). An individual might think that a smaller floor standing speaker should not need that much power, but if you have a concern beyond HT applications that you desire the best you can get out of them, the CM7’s demand at least 75 Watts of solid power, and ideally 100 Watts or more. You are not likely to get that out of a mass-market HT receiver. “ … the FST mid is one of the most tonally correct drivers I have heard in a speaker in this price category.” After laboriously scrutinizing the sensitivity, potential suitors will be happy to know that the FST mid is one of the most tonally correct drivers I have heard in a speaker in this price category. Granting less weight from the smaller cabinet and limited low end, voices were reproduced with uncanny subtlety. Combine this with excellent detail and the CM7 rings true. The speaker is not prodigious in scale, but one gets the distinct sense that the sonic signature could be laid down upon a larger speaker’s voice (in the way that tracks are laid down in recording) and not be in error.
AUDITIONING
B&W kindly supplied me with a demo disc entitled Bowers & Wilkins with Real World Records. One track in particular I kept playing over and over, “Old Blind Barnabus,” sung by the Blind Boys of Alabama, in reference to the Biblical account of a blind beggar calling out to Jesus to heal him (Technical correction: the name of the beggar was Bartimaeus (see Mark 10:46-52 in the Bible. Barnabas was a fellow missionary with Paul, the Apostle. I do not know if the Blind Boys used artistic license, or simply erred). It was genuinely thrilling to hear these jowel-cheecked baritones and basses singing with abandon. The snap of fingers keeping cadence with the piano and chorus was mesmerizing. The clarity of the voices through the FST was commendable. There was a trim, but not restricted, nature to the FST which inspires confidence that one is hearing a tight presentation. Boz Scaggs has always been one of my favorite “curiosity” artists. I say curiosity because certain performers have unique voices or playing styles. Boz’s voice is constrained-sounding in such a way that I recall a friend of my mother who had vocal chord surgery. Her voice was affected permanently, and she could only muster a strong whisper in conversation. No matter the intensity of the comment, it came out as a strong whisper. Almost anything she said was interesting because it sounded stressed but soft. I find that I listen to Boz’s voice in the same way, enjoying hearing such a unique sounding set of vocal chords. As he is aging, he’s moving toward ballads rather than pop songs. His collection entitled My Time: A Boz Scaggs Anthology reveals a terrific amount of ennui in his voice as a dejected lover in “Just Go,” and a longing for solitude in “Sierra.” One feels his pain and tiredness intensely – much of this I chalk up to the FST mid, a very clean midrange driver. It seems, however, that the CM7 was bred to rock, and this it does quite well. I was messing with the Tannoy Glenair’s (in for review), seeing what they did with older bands like Boston (Horrors! Such a fine high efficiency speaker as a Tannoy and such crass music as Boston? Oh, yeah!) when I was struck by the urge to compare the sound with the CM7. One can hardly get two more distinct speakers than these, the one having a concentric 15” paper woofer with horn tweeter, the other the tight, 3-way Kevlar-wielding CM7! It is not proper to simply compare the two speakers in a win/lose fashion as they are separated by more than $8k retail. What I was looking for was how vibrant the CM7 was with the rock music. “There have been larger floor standers where I have had to limit levels so that they would not assault the ear, but not these.” The CM7’s like to party, eschewing the polite, refined nature of the Glenair. They bit into the meat of the music and punched their way through the bass line. I wondered if I would be able to tolerate the guitars at high levels on tracks like “Foreplay/Long Time”, and pleasantly I was able to. There have been larger floor standers where I have had to limit levels so that they would not assault the ear, but not these. Even though the bass driver was pushed beyond comfortable level to begin a “pumm, pumm” rhythm, and the synth was a tad stressed, they never broke my self-imposed “noise” barrier – the point at which the music sounds like noise rather than music. This is high praise for a smaller floor stander! Music through the CM7’s seemed contextualized properly. I had just picked up Seal’s Live in Paris DVD, and put it on the Oppo 970HD going through the Pathos amps. It was perfectly grand, the 7’s in a darkened room at full stride presenting themselves as though they could be much larger. The vibrancy matched the intensity of the on-screen performance. I never gave a thought to the fact that my subwoofers had been silenced.
THE STORY OF THE FOAM PLUGS
In the tradition of the TV shopping channel QVC, “BUT WAIT! THERE’S MORE!” (Queue image of CM7’s in background with set of foam plugs foreground…), for an unlimited time, when you purchase a pair of CM7’s, we’ll include free this set of audiophile quality foam bass port bungs! Made especially for B&W, they are guaranteed to combat bass bloat!” If I were selling CM7’s in a store, I would play up these least expensive, most easily ignored elements of the speaker – the very low-tech foam port plugs! I have to laugh at the technical term employed – “bung.” I guess the word plug is not accurate and cylinder is not fancy enough. I do not speak in jest about the efficacy and necessity of these little foam wonders. I found that the bung was quite useful to integrate the speaker’s presentation. It took a bit of looking in the manual, but I did find the reference under the heading “Fine Tuning”: “If you want to reduce the volume of the bass without moving the speakers further from the wall, fit the foam plugs in the port tubes as illustrated in figure 3.” That was it; what it should have said was, “The foam plugs supplied are the means to obtaining superior performance from your speaker.” I don’t expect B&W to admit it, but the foam bungs were as critical as any other aspect of this speaker’s performance! speaker’s performance! Granted, foam bungs are not the kind of things I typically get excited about, but what was exciting to me was the impact these silly foam pieces had on the speakers! Sometimes audio is an experiment in centimeters, either in placement of speakers or a sound panel, etc. My logic was that a foam plug would effectively attenuate the bass as it was inserted in varying depths into the port. It worked marvelously well! I felt the speaker was bass emphasized without the plug. I experimented with two primary options: 1. No Plug, resulting in an earnest bass with unacceptable distortion at higher levels, or 2. Plug inserted fully, resulting in a more subdued bass, but with more emphasis on the treble making it a tad too stiff. “The happy news is that the CM7, to a degree, can be tuned to taste.” The solution was to pull the foam insert out approximately two thirds. Ahhhh! The integration of drivers was complete! (Sounds like a mad scientist, “We have achieved the integration of the drivers! It Lives! It LIVES!”) The bass was meaty but not meandering and the treble was complimentary to it. Now I could bob my head and relax as I increased listening levels. While this may seem absurd to some readers, such precise positioning of the plug had important consequences in my room. The happy news is that the CM7, to a degree, can be tuned to taste. It took some fiddling with the plug to get there, but once the Goldilocks setting was reached, the sound was just right! When I mention such a seemingly unintuitive tweak, it is only because it made a significant contribution to the overall sound. If the foam bung didn’t make that much difference, I would have conceded that one had to live with a bass or treble emphasis in the CM7’s. No, the plug position did not make the speaker suddenly take on different tonality or make it jump into a higher echelon of speakers, but it did make it perform much more like a well balanced speaker. That is also the conclusion I reached regarding the CM7 - that it is a vivid sounding, yet well balanced speaker. It’s notoriously difficult to make a small floor stander with satisfying bass, and it’s not an easy thing to make a monitor with an appealing upper-end. B&W has done well on this account as they have made the CM7 a superb-sounding Compact Monitor for use as mains, especially so in a HT oriented system.
Also read Doug Schroeder’s article on: Thou shalt not listen to any solid-state integrated with stock jumpers!
Thou shalt not skimp on power cords!
Solid-state DAC
Solid-state preamplifier & monoblock amplifiers
Solid-state Integrated amplifier
preamplifier
tube hybrid integrated amplifier
with Dussun V8i
Jena Labs "Jazz" & "Java" cables
tube amplification system
MIT AVt MA cable system & Z-Stabilizer
CD player
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Comments: editor@dagogo.com ©Dagogo 2007 |
