Bowers & Wilkins CM1 S2 Bookshelf Speaker Reviewed

Published On: January 19, 2015
Last Updated on: October 31, 2020
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Bowers & Wilkins CM1 S2 Bookshelf Speaker Reviewed

Bowers & Wilkins recently updated its entire CM Series lineup. Brent Butterworth sits down with the CM1 S2 mini-monitor, which at $1,100/pair is the least expensive model in the group.

Bowers & Wilkins CM1 S2 Bookshelf Speaker Reviewed

  • Brent has been a professional audio journalist since 1989, and has reviewed thousands of audio products over the years. He has served as editor-in-chief of Home Theater and Home Entertainment magazines, contributing technical editor for Sound & Vision magazine, senior editor of Video magazine, and reviews editor of Windows Sources magazine, and he also worked as marketing director for Dolby Laboratories. He's now on staff at Wirecutter.

BowersWilkins-CM1-life.jpgWhy would a manufacturer want to change a perfectly good speaker line? It could be to incorporate a new technology or some ingenious design twist; but, in the case of the Bowers & Wilkins' recently updated CM Series, it looks to me like the reason boils down to screws.

The previous version of B&W's CM1 mini-monitor had a total of 10 screws on its front baffle: six to hold the woofer and four more to secure the tweeter. That was perfectly fine 10 years ago because almost every speaker had screws on the front then. However, more and more speaker companies are following Apple's lead and eliminating most or all of the visible fasteners on their products. The new B&W CM1 S2 has a few small screws visible on the back, but none on the front. The new design also eliminates some of the metal accents that tarted up the old CM1's front baffle. It's now an elegant-looking little speaker, whether it's wearing a satin white, gloss black, or rosenut finish.

There is some new technology in the CM1 S2, most notably the double dome decoupled tweeter. The tweeter's dome is like two laminated aluminum domes with the center of the rear dome cut out. The result is a diaphragm that's much stiffer around the edges, where it receives all the force from the voice coil, yet only a little heavier than a conventional aluminum dome. This should result in lower distortion - and it should shift what distortion there is up to higher and less audible frequencies. A ring of gel decouples the tweeter assembly from the speaker cabinet, so it's affected less by the much more powerful vibrations of the woofer.

Like most of the tweeters in B&W's speakers, this one has a Nautilus tube: a long, tapered tube on the back that absorbs all of the sound waves coming off the back of the aluminum dome so that the sound waves can't affect the operation of the dome or "leak through" the diaphragm. This is the same principle by which transmission-line speaker cabinets work, and in my experience it works very, very well.

The midrange/woofer uses the same design B&W's been working with for a while, with a yellow woven Kevlar diaphragm that was chosen because of the fiber's extreme tensile strength, designed to provide a smooth, articulate midrange and distortion-free bass. The back panel has a port for the midrange/woofer and dual metal binding posts. A magnetically attached fabric grille is included.

At $1,100 per pair, the CM1 S2 is the least expensive speaker in the revised CM line, which includes two other bookshelf models, three towers (including the CM10 and CM6 S2 that we previously reviewed), two centers, a surround, and a subwoofer.

The Hookup
I placed each CM1 S2 atop one of my Target metal stands, each of which is filled with kitty litter to give it more weight and prevent the metal from ringing. I used Blu-Tak poster adhesive to secure them to the stands.

The back corner of each speaker sat 26 inches from the wall behind it. This gave me a reasonable amount of bass, at least for a mini-monitor. I tried pushing the speakers back closer to the wall to reinforce the bass, but this action tended to make the bass sound excessively punchy, probably because it emphasized the rear port's resonant peak. Because these speakers don't produce a lot of bass, they're easy to position; the more bass a speaker has, the more its performance is affected by room acoustics.

I used my usual system for the review: a Krell S-300i integrated amp, fed signals from a Sony PHA-2 USB headphone amp/DAC connected to the Toshiba laptop on which I store most of my music. I also used a Music Hall Ikura turntable routed through an NAD PP-3 phono preamp.

The grilles had almost no audible effect. I left them off because the speakers looked so much better that way.

Mini-speakers have a rep for open sound, a broad soundstage, and precise imaging. That's for two reasons: 1) because the enclosures are narrow, the diffraction off their side corners isn't so troublesome; and 2) because many mini-speakers use small woofers, which have broader dispersion at high frequencies than large woofers do. Of course, this is just generalizing. There's no reason a tower speaker can't have these traits, which is why I hate it when I audiophiles assume mini-speakers have better spatial characteristics. Sadly for me, the CM1 S2 will only encourage such generalizations.

This little speaker produces such a spacious soundstage, and such realistic imaging, that I'd almost consider it a must-hear for anyone just getting interested in audio. Speakers shouldn't sound like their sound is coming from a box. They should sound like the sound just appeared in space in front of you...and that's what the CM1 S2 sounds like.

"Very very very good," I noted when I played "Midnight Voyage" from saxophonist Michael Brecker's now-classic Tales From the Hudson. I found it hard to decide whether I was more impressed by the CM1 S2's reproduction of the tenor sax, the guitar, the piano, or the drums. That's because the timbre of the speaker accurately portrayed every instrument without favoring any.

I guess I'd have to say it was the drums in "Midnight Voyage" that really killed me. The little B&W has a way of imaging cymbals, in particular, that sounds incredibly real. You can hear the precise placement of each cymbal in the kit; many lesser speakers portray multiple cymbals as more of a formless wash of high-frequency energy. Accurate cymbal imaging is especially important because, in many recordings, the only real stereo information is from the stereo mics placed over the drum kit. Most of the other instruments are usually recorded with a single microphone and "steered" to a certain place in the stereo soundstage using the left/right pan controls on the recording mixer or in ProTools.

michael brecker-midnight voyage.wmv

After hearing what the CM1 S2 did with "Midnight Voyage," I couldn't resist putting on another sax player: altoist Kenny Garrett playing "Sing a Song of Song" from the Songbook CD. And again, as real as the sax and piano sounded, it was the drums that blew me away. Not just the cymbals this time, either. I loved the way the CM1 S2's little five-inch woofer captured the punch and precision of the smaller kick drum that jazz players (in this case, Jeff "Tain" Watts) use instead of the big sonic cannons most rock drummers prefer. The dynamics of Watts' cymbals and rimshots also came through remarkably well, thanks to that double-dome tweeter, I suppose.

Kenny Garrett - Sing A Song of Song

One of my favorite stereo soundstaging tests is Adrian Belew's "May 1, 1990" from the album titled Here. In this tune, Below resorts to all sorts of sonic trickery, such as panning a ticking clock around in the intro and playing with the width of his voice and an acoustic piano by mixing them hard-center then blowing them out to fill the room. (It probably seems stupid when you read about it, but the tune has a fantastic groove, and the effects play into the emotional content of the song.) The CM1 S2 completely blew me away with the way it filled the room on this tune. It reminded me of the spacious sound I've heard from dipole panel speakers like MartinLogans and Magnepans, but with more precise, pinpoint imaging than those speakers can deliver.

The CM1 S2 is no heavy rock speaker - and we'll get to that shortly - but I have to say I found it incredibly involving when I played "Highway Star" from Deep Purple's live album Made in Japan. Made in Japan was recorded in a quaint era when live rock recordings included some of the ambience of the venue itself, especially at the beginning of the opening tune, "Highway Star." Through the CM1 S2, I could clearly hear Ian Paice's snare drum echoing off the walls of Osaka Festival Hall as he prods the band into the tune. As the volume rose, I was amazed to hear how clearly and cleanly the CM1 S2 reproduced Ian Gillan's voice, even during his epic screams in the chorus. Although there wasn't much bass, I found myself furiously tapping my foot anyway.

Deep Purple - Made in Japan - Highway Star (video)

Click over to Page Two for Measurements, The Downside, Comparison & Competition, and Conclusion...

Here are the measurements for the Bowers & Wilkins CM1 S2 speaker. Click on the photo to view the graph in a larger window.


Frequency response
On-axis: ±3.9 dB from 50 Hz to 20 kHz
Average: ±3.0 dB from 50 Hz to 20 kHz

Minimum 3.8 ohms/20 kHz, nominal eight ohms

Sensitivity (2.83 volts/one meter, anechoic)
81.0 dB

The chart above shows the frequency response of the CM1 S2. Two measurements are shown: at 0° on-axis (blue trace) and an average of responses at 0°, ±10°, ±20° and ±30° (green trace), all measured on the horizontal axis. The main characteristic you'll notice in these measurements is that the upper midrange and lower treble energy is reduced relative to the bass and treble. Between 1.5 and 7 kHz, the output dips from -2 to -5 dB, with the strongest reduction between 1.5 and 4 kHz. I didn't hear anything like a "recessed" midrange, which this measurement would seem to indicate, but I bet it's the reason I perceived the tonal balance as trebly. Averaged off-axis response is excellent, barely differing from the on-axis response, but that's the norm with speakers this small because the smaller the driver, the broader the dispersion.

These measurements were done without the grille. The effects of the grille are limited to very high frequencies where they aren't very audible: just one dip between 9 and 11 kHz, maxing out at -3.6 dB.

Sensitivity should be about 84 dB in-room (I measure anechoic sensitivity for the sake of consistency), which means you'll need 32 watts to get to 99 dB. That's not great sensitivity, but you probably don't want to be playing a little speaker like this real loud, anyway. Impedance averages about eight ohms, so you should be able to run this speaker off practically any amp.

Here's how I did the measurements. I measured frequency response using an Audiomatica Clio FW 10 audio analyzer with the MIC-01 measurement microphone and the speaker driven with an Outlaw Model 2200 amplifier. I used quasi-anechoic technique to remove the acoustical effects of surrounding objects. The CM1 S2 was placed atop a 78-inch (100-cm) stand. The mic was placed at a distance of one meter. Bass response was measured using ground plane technique, with the microphone on the ground one meter in front of the speaker. Bass response results were spliced to the quasi-anechoic curves at 230h Hz. Results were smoothed to 1/12th octave.

The Downside
The CM1 S2's tonal balance tends toward the trebly side, although that's not because the treble is boosted; it's because the bass output of the five-inch woofer is limited. For example, when I played "Ms. Julie" from Larry Coryell and Philip Catherine's Twin House (best acoustic guitar duo ever, IMHO), the recording had perhaps the biggest sense of space I've heard since I first bought it on eight-track when it came out in 1976. Yet it sounded too thin; the guitars lacked body, sounding almost like someone had stuffed them with attic insulation.

But the main thing that will rule the CM1 S2 out for many listeners is its lack of deep bass extension. There's only so much you can do with a tiny enclosure and a five-inch woofer. This means that, for anyone who wants to listen to a lot of heavier pop and rock on their system, the CM1 S2's sound is too lightweight. Listen to R.E.M.'s "7 Chinese Brothers," and you'll hear what I mean. The bass line is somewhat lost...and the kick drum, too. The thinness of the sound made it seem to me like the upper midrange, around two kilohertz, was boosted a little. And you know, it's not like R.E.M. is some kind of heavy metal group.

REM - 7 Chinese Bros

Comparison and Competition
There aren't a whole lot of compact bookshelf speakers in the $1,000/pair price range that would compete with the $1,100/pair CM1 S2. The reason for that is obvious: Most people, if they're spending $1,000/pair, would prefer to get tower speakers that can deliver deep bass. That said, I can think of four mini-speakers that would be obvious competitors for the CM1 S2: the Monitor Audio Silver Series 1 ($899/pair), the Paradigm Studio 10 ($1,098/pair), the PSB Imagine B ($1,099/pair), and the SVS Ultra Bookshelf ($998/pair). I've heard the first two briefly and have lots of experience with the latter two. I expect that all of these speakers, with the possible exception of the Paradigm Studio 10, will give you more robust sound and a fuller-sounding tonal balance than the CM1 S2. To my ears, the CM1 S2 is a bit of a lightweight even among mini-speakers.

Then again, I seriously doubt any of the above speakers will deliver the dramatic soundstaging, imaging, and spatial effects that the CM1 S2 offers. Is that just because the CM1 S2's tonal balance is tilted up? Maybe, but I doubt it. I think there's something special going on with B&W's double-dome tweeter. It's a big part of the reason I loved the original CM10 when I reviewed it earlier this year.

Obviously, the CM1 S2's applications as a full-range speaker in a two-channel stereo system will be limited to people with specific taste. I'm sure it'll find plenty of use as a surround speaker in systems with B&W's larger CM Series speakers, and I expect some people will mate the CM1 S2 with a subwoofer to fill the sound out a bit. But considering how difficult it can be to get a subwoofer to work with a two-channel system, I'd say if you want deep bass in your stereo system, get a bigger speaker.

This is definitely not going to end like one of those "buy it, you'll love it!" reviews. The CM1 S2 isn't that speaker. It's a speaker tuned for people who want to hear tons of detail, dramatic soundstaging, and lifelike imaging, but who don't much care about deep bass. That description fits a lot of audiophiles. It also fits most jazz, classical, and folk fans. For them, the CM1 S2 is a costly but fantastic choice.

Additional Resources
Bowers & Wilkins CM10 Floorstanding Speakers Reviewed at
Bowers & Wilkins Launches New CM Series at
• For more speaker reviews like this one, check out our Audiophile Bookshelf and Small Speakers section at

  • bobbg
    2015-02-03 12:01:36

    Nothing Like Deep Purple Live in Concert....... In person. Are we getting old or what?

  • Kot Begemot
    2015-01-27 20:14:33

    I have the previous gen model of CM1 and in my second listening room (16 by16) there is none of the thinness, or light balance you speak of. On the contrary the sound is dark, full and even, without emphasizing any frequency region. With truly good tube amp (in my case Red Rose 1) the CM1a produce a panorama of lush, and precise sound with very well defined and ample bass as well. With reference level solid state amp (hint: not your Onkyo-like sounding Krell integrated) the bass is really taut and defined. As far as comparison: in my opinion these CM1s produce much more musically truthful and textured sound than ANY models of those manufacture that you mention regardless of cost. And yes I ve heard the other ones, and been around live classical and jazz performances/recording, as well as other genres of music, not to mention "audiophile" scene in NYC area for the last 27 years. I'd go as far as to say that CM1 produce sound textural & electrostatic like sound down to 50 hz that most politically correct&reviewer favorite "pet" speakers up to 10 grand can only dream about.... The only other monitor that I liked as much were the legendary Ensemble PA-1. In mine not so humble opinion the CM1 and CM5s are the speakers that most serious MUSIC LOVER could ever need in normal listening size rooms up to $15 thousand.... They are that good!

  • Josh Casteel
    2015-01-22 05:07:46

    Great review, I'm using the S1's in a 2.1 setup for the living room. Found them at less than half price at the local Best Buy and couldn't pass it up. They too image very well.

  • Colonel Gurlukovic
    2015-01-21 00:15:17

    Yea I did. I didn't mean it to sound like your review and rating don't match at all, just that, for all the praise , and the only real downside being limited bass power (expected in a small standmount), the rating was just unexpectedly low compared to htr's other reviews of speakers. I'm not trying to sound negative and say "gotcha!", I'm just commenting on my perception of your praise vs. Criticism ratio. I would be really curious to hear how you compare these to the REVEL M105. Every time I hear the m105 it blows me away. Makes goldenear triton sevens sound like poo.

  • Brent Butterworth
    2015-01-20 23:19:33

    Did you read page 2? Significant downsides here.

  • Mel Famie
    2015-01-20 12:24:42

    Ah, thanks! Does the ring just pop off?

  • chuckdaly
    2015-01-20 12:07:58

    The ring around the drivers hides the mounting screws.

  • Mel Famie
    2015-01-20 11:33:28

    The upper midrange dip is interesting. Very "high end audio". With the blind mounting, how are the drivers removed in case of need of servicing?

  • Colonel Gurlukovic
    2015-01-19 22:22:52

    Interesting... the praise seems incongruent with the rating. Has HTR changed their rating practices? I find this curious, because I recently posted on this exact phenomenon , and now it appears!

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