SOPWAMTOS and CNO Review Continued

In the previous post, I wrote that Troels’ CNO-T25 compares favorably to my Spendor SP2/3, but I didn’t give a whole lot of description of the sound.  I’ll give some more impressions here, but first some caveats.  I’m not trying to do a professional style review where I try the speakers with different amps and cables and different room placements and cite the recordings I listen to and so on.  So this is just what I hear with my system in my room, your mileage, as they say, may vary.

I truly admire the Spendor company in this day when many companies have changed owners and are a familiar brand name but with little connection to the original company.  Spendor also has had some ownership changes, however many of Spendor’s employees have been there for a long time, and the current owner knew the founder Spencer Hughes (Spendor = Spencer and his wife Dorothy).  Current Spendor management, in my view, has shown respect for the Classic line by making limited refinements.  So Spendor is a rather different from many companies whose name may imply some great European or other heritage but in fact they are now owned by a big conglomerate and their products are manufactured say in China.  Spendor is a true manufacturer in that they build their own cabinets, they build their own woofers, they assemble their speakers, including the crossovers, all in the factory in England (the tweeters are made by Seas, same company that makes drivers for a lot of great speakers, including the CNO).  Spendor could be a member of SOPWAMTOS, founded by Bruce Gordon the bicycle builder – that’s the Society Of People Who Actually Make Their Own Sh*t, as opposed to companies that outsource production and just stick their brand label on the finished product, see

And this is kind of random, but speaking of sticking your brand label on another company’s product, have you read about the Aston Martin Cygnet? With a new Bond movie out, Aston Martin is getting some more publicity, but I don’t think James Bond would chose the Cygnet as his getaway car.  Yeah they (Aston Martin) paint it and make the interior with fancy leather and trimmings, but it’s still a Toyota Scion iQ:

Back to audio, I hesitate to go overboard with comparisons to my pair of Spendors for several reasons.  First of all, my speakers are not the same as a current model that blog readers could go hear.  Spendor does have a model SP2/3 (called R2, the second revision) in its current lineup, and it looks the same and has the same (or nearly the same) dimensions as the older model, it is actually a different speaker – slightly different cone material, different woofer, different tweeter, and so on, although designed by some of the same people (Terry Miles) and with some similar design goals; you can read about it here:

Anyway, I fed a mono signal to the CNO and to the Spendors, and switched back and forth, and here are the impressions.  They don’t sound the same, but the difference is somewhat subtle – they are both neutral enough that nothing jumps out at you when you switch.  The SP2/3s are definitely warmer, they have a little more closed in sound, they are smooth and a little more laid back in the upper midrange.  The CNO’s are both leaner in the lower midrange and have more bass – they have a clearer, more detailed sound.  Does that sound contradictory – leaner but more bass?  That’s how I hear it.  High frequencies to me are not noticeably different – it’s not like one speaker is “brighter.”

I am speculating here, but the Spendor has a relatively wide baffle, and the CNO has a narrow front baffle, and I think that the wider baffle may contribute a bit to the more diffuse and warm sound of the Spendors.  As I wrote before, the CNO has a more spatious sound, I imagine a pair of them would create a different and perhaps more precise stereo image than the Spendors.

I have a secondary audio system for watching movies/television with a pair of Bowers and Wilkins 601s (the original ones) fed by an older NAD receiver and an Adcom DAC, pretty good, but not real high end stuff.  As a test, I created a mismatched stereo pair with the left speaker being the CNO and the right speaker the B&W 601.  Wow.  The CNO is a much better speaker.  The B&W has an attractive tonality, and movies sound good.  But listening to music with the 601s didn’t excite me, but just adding one CNO made a huge difference – the music was much clearer, more dynamic and exciting.

A few more brief comparisons.  I had a listen to Bowers and Wilkins PM1, and also their 805 Diamond speakers.  Of course, different amp, different room, so it’s not apples to apples, but here are my impressions.  The PM1 at first impressed me, but then I listened to a male pop singer (Michael Buble) and started hearing an emphasis on sibilants and a certain nasality, I felt disappointed.  The 805 Diamonds were very clear – my son listened with me and felt their clarity was better than the CNO, but I found the sound sterile and uninvolving.  Take that with a grain of salt.  What I think is so great about the CNO is the balance between clarity and making music enjoyable to listen to.  Although I listen mostly to jazz and smaller chamber or solo classical music, my teenage sons like their pop and compressed mp3s, and they sound good on the CNO.

One more thought about the CNO.  Although it is presented on Troel’s site as a floorstanding speaker, I had good results making it as a monitor style speaker.  Here is a particularly interesting monitor mplementation using vertically stacked slices:, and you can imagine that if the port was in the rear the speaker could be fairly compact.  Because of the narrow front baffle, and depending on how tall you make the cabinet (if the port is in the rear, it could probably be a fairly compact 14″ or so in height), it doesn’t take up a whole lot more space than many so called “mini-monitors,” but it’s a much more full bodied sounding speaker than the ones I’ve heard with smaller 5″ or 6″ woofers.  So it’s a versatile design and I think competitive with loudspeakers that sell for quite a bit more (these days, the Spendor SP2/3s cost about $4,300) than the cost of DIY CNOs.

So that’s a wrap for comparisons.


Speaker Review: Comparing Troels Gravesen’s CNO and Spendor SP2/3 Loudspeakers

This is one of my most popular posts, so I want to make sure to point out that this is the first of two posts comparing the CNO and Spendor SP2/3, the second post is:

Originally I titled this “Zen and the Sound of One Speaker Pulsing” as a takeoff on the famous Zen question, “What is the sound of one hand clapping?” as I only have a single CNO speaker.  I built the CNO-T25 loudspeaker, designed by Troels Gravesen and using Seas Excel drivers (see and CNO-T25.htm), as a center channel for music and matched up with a pair of Spendor SP2/3 loudspeakers.  The Spendor SP2/3 speakers are semi-famous, they are a simpler version in a lineage (the BC1, then the Spendor SP1, etc.) based on BBC designed loudspeakers for broadcast monitoring.  One online review of the Spendor SP2/3 is; a few quotes, “It’s that damn good.  Get the picture?” and “one of the most musical sounding speakers that I’ve ever had the chance to hear. They surprised me by their levels of transparency and detail…”

My Spendors are 18 years old, are they past their prime?  Hard for me to know, but they sound good to me, perhaps the bass is less than when they were newer, perhaps some of the clarity has declined over time.  The new Spendor SP2/3s look the same but are completely different speakers (new woofer, new crossover, new tweeter, new cabinet, etc.), and I haven’t heard them to compare.

At any rate, here are some thoughts about the sound of the CNO-T25.  The CNO-T25 compares favorably to the Spendors, and I consider that high praise. While the CNO-T25 does not sound exactly like the Spendors, the combination works well together for music, especially since for many recordings the position of voices/instruments is fixed for a recording (I suppose a live recording of say a musical or opera might be an exception), so slight differences between the center and left/right speaker are less critical.   In my opinion, the CNO, with a 24 litre cabinet, has better bass, more clarity, and seems more dynamic.  Spendor loudspeakers are famous for their magical, seductive midrange quality.  I would say that for pure tonality, the Spendor SP2/3s are hard to beat. But the clarity of the CNO was quite noticeable to me, the aural equivalent of suddenly looking out a freshly cleaned window and realizing how dirty the window actually had been.

Since I only built one CNO speaker, I don’t really know what a stereo pair would sound like, but if it’s not a complete oxymoron to state, it seems that the CNO has a spatious sound, even in mono. The sound doesn’t change much as I stand up or sit down, or as I move around the room, an important quality for me. To contrast, I briefly auditioned some Dynaudio speakers and they sounded great when I was in the sweet spot sitting down, but if I got up and walked around the room, the sound changed a lot.  So not all speakers have the property of an “even power response” – sounding about the same in different listening positions.

While the CNO-T25 isn’t meant for killer volumes, it easily fills my large listening room at what I would call reasonable listening levels.  Perhaps because of the clarity, it is tempting to play it louder than the Spendors, and while the CNO sounds fine at low volume levels, it comes alive with a bit more volume than the Spendors.  And, something very important to me, both the CNO-T25 and the Spendors are enjoyable with less than ideal recordings.  I remember when I was auditioning the Spendors, the dealer also had a pair of Spendor SP7/1 speakers, and it made most of my recordings sound bad, so I said no thank you.

Could you tell Color from Black and White?

Before I wrap up the posts about the science experiment listening to stereo and mono versions of the same audio clip, let’s discuss an analogous science experiment with vision.  And I recognize that the most obvious visual analogy would be 3D versus non-3D, but for the sake of argument suppose we conducted an experiment to see if people with normal vision (no known diseases or color deficiencies) could tell the difference between a color and a black and white version of the same video clip.  So, here’s the protocol: a subject is told that they will watch the same video clip three times, and that two of the times will be the same, and one time will be different. And in fact, in randomized fashion, two of the three playings are identical, and one version is color (say the original), and one version is black and white which is created by converting the original color video.  The subject is not told what the difference between playings is, the subject watches the three playings of the video clip, is asked to identify the video clip that is different, and is asked to identify which playing he/she preferred.

Now, what would you expect?  I would expect that the difference between the color clip and the black and white clip would be so obvious that the subject would definitely identify correctly the video clip that is different.  And, while I suppose there can be artistic reasons sometimes to prefer black and white (Woodie Allen, for example, sometimes shoots portions of his movies in black and white), for most video clips that are originally filmed in color, I would expect the subject would prefer the color version.  As I revealed in the previous post, listeners were only correctly aware of a difference in stereo versus mono playback about 50% of the time.  Yet we would expect viewers to be correctly aware of a difference in color versus black and white about 100% of the time.  To me this means that for most listeners, the “stereophonic” aspect of music playback is relatively unimportant especially compared with the importance of color to vision.

Now a different version of the audio experiment would be to tell the subject the purpose of the experiment and to train them to hear the differences.  Similarly here, a different version of this visual experiment would be to tell the subject, “we are investigating whether you can tell the difference between color and black and white.”  However, I don’t think that would change the results for the color/b&w experiment.  It might change the results of the audio experiment though.

The Negative Connotation of Mono, and The Real Reason Stereo is Superior

Why is mono sound regarded as inferior?  Back in the day, people listened to mono sound coming from a single speaker.  As stereo recordings and broadcasts became popular, the use of two speakers for playback became common, and stereo was widely regarded as superior to mono. But for many listeners, and in many listening situations, I argue the real difference and advantage of stereo is not the two channel recording, it is the multispeaker playback.

There are recordings where the difference between stereo from two speakers and mono from two speakers is only subtly different.  But mono from two speakers and mono from one speaker is significantly different.  Said another way, if you are listening to a two channel audio system with two loudspeakers, and you switch the source from stereo to mono, the difference might not be obvious, but if you switch from using two speakers to just using say the left speaker the difference is both dramatic and obvious.  Now, whether mono from two or three speakers is inferior to stereo from two or three speakers is another matter.  As an oversimplification of the complete results, to be discussed in a later blog post, the little science experiment on stereo versus mono showed that listeners were only correctly aware of  a difference in stereo versus mono playback about 50% of the time, which  is about the same as random guessing.  Of course, there might have been different results if the listeners had been trained and told to listen for the difference between mono and stereo, but that just points out that it’s not a natural and obvious difference.

It is interesting to see how the notion of mono sound as inferior keeps showing up in the media.  For example, unless you have little interest in techie gadgets, you have read about Apple’s new iPad Mini.  Among its alleged shortcomings – mono sound! Horrors to imagine that such a small device would not have stereo speakers!!!  For example, see:  I would claim this is all kind of silly – the tiny, tinny speakers in these little tablets can’t possibly sound very good whether they are mono or stereo, if you want decent sound you’ll need headphones or a larger external speaker system.  And, I would happily prefer to listen to a single, superior mono speaker instead of two inferior stereo speakers, especially when the separation between the speakers is a few inches.

Steve Guttenberg, who writes the CNET blog Audiophiliac, also touched on the subject of Mono in a recent post:  He argues that as we see more all-in-one loudspeakers, sound reproduction is becoming essentially monophonic (there is little difference between 2 loudspeakers close together compared with a single loudspeaker).  Maybe if “mono” didn’t have such negative connotations in the minds of consumers, we would see higher quality mono loudspeaker systems instead of inferior stereo ones.

The Great Sixth Grade Stereo vs Mono Science Experiment Part I: Description and Procedure

Last year my son Noah, then 11 years old and in sixth grade, was looking for an idea for a science project.  As I had recently (a few months) completed the Troels CNO-T25 ( and was experimenting with 3 channel stereo, I suggested an experiment.  The experiment was prompted in part by my observation that it was not always obvious to me whether I was listening to mono or stereo (from two speakers), and the difference was even more obscured with sound coming from three loudspeakers.

I went to some lengths in earlier posts to explain that mono does not mean “sound coming from one speaker” – mono can mean sound from multiple speakers, it is just the same source signal.  I will go into some detail about the experiment, but as a brief summary subjects were not told the purpose of the experiment or other details, and they showed no awareness of when they were listening to mono versus 3 speaker stereo, and in some cases they preferred the sound of mono!  I think this experiment has important implications for how all-on-one speakers (e.g., iPod docks, Zeppelin Air, etc.) are, or should be, designed. More about that later.

Before describing the actual experiment, I would like to explain what experiment I ideally would have liked to conduct, and why we did a compromise experiment.

Have people listen and compare the following setups: 3 identical front speakers being fed a mono signal (same signal to all 3 speakers) versus a level matched stereo signal divided by Dolby Pro Logic II to the center/left/right speakers (level matched as the resulting volume of 3 speakers in mono might be louder than 3 speakers in Dolby Pro Logic mode).

We didn’t have 3 identical front speakers, and subjects might detect a difference between 3 speaker stereo and 3 speaker mono based on tonal or other differences between the center and left/right speakers.  We also had no ability to precisely level match between mono versus stereo trials.  We could have compared two speaker mono with two speaker stereo, that would have been less interesting.

Test Question: Can people tell the difference between mono and stereo playback (using 3 loudspeakers for playback)?  Is mono or stereo preferred?

Procedure: Two sample songs were imported into a MacIntosh computer from compact disc recordings using Apple Lossless format.  During playback, the Mac was configured
to either play “stereo” (different left/right channel sound) or “mono” (the left and right channels are combined so both are the same, however there are still two channels of output).  The songs were played with iTunes, and the output of the Mac was sent by digital optical cable to a Rotel processor in “Dolby 5” mode, which sends the left channel input to the left speaker, the right channel input to the right speaker, and the combination of the two channels to the center speaker.  When switching the Mac from mono to stereo, there is no change in volume or balance between the speakers, the difference is that, coming out of the Mac, the left and right channels have different signals in “stereo” mode, whereas the left and right channels have identical signals in “mono” mode.  In terms of what the listener hears, the center channel speaker produces the same sound in either stereo or mono mode.  For the left/right speakers, however, mono/stereo is different: when the Mac is configured for mono, the left and right speakers produce the same sounds, whereas when the Mac is configured for stereo, the left and right speakers produce different sounds.

Test subjects listened to a one minute portion of song A three times, and were told that two of the times would be alike and one time would be different.  Then they listened to a one minute portion of song B three times with the same protocol as for song A.  The subjects were not told the purpose of the experiment, and were not told what was different between versions (no mention of mono or stereo or playback settings).  The subjects were asked to identify which of the three playings of song A was different, and which playing they liked best.

Two people conducted the experiment, my son and I.  To have a double blind procedure, one person operated the computer and one person interviewed the test subjects and
recorded results; only the person operating the computer knew whether the song was being played in mono or stereo.  The person operating the computer played the same
song three times so that (in random order) one time was mono, one time stereo, and one time was either stereo or mono.

There were two sample songs: song A was the pop song “Beautiful Monster” by Neo.  While the recording for song A is “two channel” with different sounds in the left and
right channel, it is not an acoustic stereo recording, and likely most of the vocals and instruments were recorded in mono and then artificially mixed to create the
final two channel recording.  Song B was a jazz tune “China Boy” that seems like a “real” stereo recording with Ken Peplowski (clarinet) and Frank Vignola (guitar).  I
found a youtube clip of Ken and Frank playing Tiger Rag, sort of gives the idea of China Boy:

In the next blog post I’ll discuss the results.