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ATC SCM19 Bookshelf Speaker Review

amirm

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#1
This is a review and detailed measurements of the original ATC SMC19 speaker. There is now a second variation with their in-house tweeter. This is the original which I call "V1." The V2 costs US 4,000 which I assume what the V1 cost. It was kindly sent to me by a member for testing.

The SCM19 is by far the heaviest bookshelf speaker I have tested. You or I should say I, could barely lift it up to the 5 foot high measuring platform. It clocks at whopping 40 pounds! Overall look of the unit is on the serious side with a damped industrial looking woofer with seemingly long travel capability:

ATS SCM19 Bookshelf Speaker Stand-Mount Monitor Review.jpg


My impression from feeling and picking up the unit was that this is going to be one dynamic speaker.

The back panel shows lack of port and dual binding posts:
ATS SCM19 Bookshelf Speaker Stand-Mount Monitor Back Panel Review.jpg


Zooming in we see the pedigree of the speaker:

ATS SCM19 Bookshelf Speaker Stand-Mount Monitor Binding Posts Review.jpg


Designed and manufactured in Gloucestershire, England.

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise. Both of these factors enable testing in ordinary rooms yet results that can be more accurate than an anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.

I used over 800 measurement point which was sufficient to compute the sound field of the speaker.

I usually use the tweeter center as the measurement axis. The manual for SCM19 states that the acoustic center is between the tweeter and woofer rings so I compensated for that by lowering the measurement center to be 4 centimetres lower. This made a tiny difference (likely due to size of the speaker and my measurement distance).

Spinorama Audio Measurements
Acoustic measurements can be grouped in a way that can be perceptually analyzed to determine how good a speaker can be used. This so called spinorama shows us just about everything we need to know about the speaker with respect to tonality and some flaws:

ATS SCM19 Bookshelf Speaker Spinorama CEA2034 frequency response measurements.png


What??? The heck kind of response is this? Giant boost in midrange and lower treble?

On top of that we have directivity mismatch when the woofer hands the signal to the tweeter. The former's beam is narrowing while the tweeter's is wide resulting in off-axis sound in that region to have different tonality than direct. In a reversal fortunes, the off-axis looks more proper:

ATS SCM19 Bookshelf Speaker Spinorama CEA2034 early window frequency response measurements.png


Putting the two together we get a predicted in-room response of:

ATS SCM19 Bookshelf Speaker Spinorama CEA2034 Predicted In-Room frequency response measurements.png


We are going to have too little bass with a lot of mid-range and presence. Given how important bass is to our perception of fidelity (about one third), this seems like the wrong choice of response.

I expected the mean looking woofer and high price of the unit to result in very low distortion. But that was not accomplished either:

ATS SCM19 Bookshelf Speaker relative distortion measurements.png


Here it is in absolute level:

ATS SCM19 Bookshelf Speaker distortion measurements.png


The beam width (how wide the region with close tonality is) on the horizontal axis is on the low side at +- 50 degrees:

ATS SCM19 Bookshelf Speaker beam width measurements.png


Here it is in 3-d diagram:

ATS SCM19 Bookshelf Speaker horizontal directivity measurements.png


And vertical:

ATS SCM19 Bookshelf Speaker vertical directivity measurements.png


Lack of port removes one of the peaks in our impedance curve:

ATS SCM19 Bookshelf Speaker impedance and phase measurements.png


We see a "kink" in the impedance/phase graph at around 700 Hz indicating resonance. That is also the point of high distortion. It also shows up in CSD/waterfall display:

ATS SCM19 Bookshelf Speaker CSD waterfall measurements.png


Speaker Listening Tests
You all keep asking me to listen to the speaker before measuring. So this time as the system was crunching the equations I did precisely that, fully biased on the incredible heft of the speaker and beefy speakers expecting to be blown away by the dynamics.

The "5 second" impression was an incredible presentation of high frequency notes. They sounded like they were jumping out of the speaker and reaching toward me. I thought, "oh yeh, this is going to be good!" Then the vocals came. Hmmm. They don't sound right. But yet, enough audiophile tracks. Let's queue up some bass heavy tracks.

What? Where is the bass? What is that woofer doing? It sure is not moving much. I turned up the volume but now the mids and highs were getting quite loud and annoying.

At this point I stop and get the measurements and see the lack of bass. So I pull up the EQ in my Roon player and put on my surgical outfit to fix what shouldn't need fixing. First thing I did was put in a low shelf to boost the bass:

ATS SCM19 Bookshelf Speaker Stand-Mount Monitor Correction Filter.png


That is filter Band 2. Was happy for 10 seconds until I turned up the volume and the woofer bottomed out! I thought for sure it could handle that 2 dB peak. But no, it was not happy at all.

Suspecting that the problem was deep bass, I dialed in Band 3 which cuts out the lowest bass registers. This has minimal impact on amount of bass but nicely eliminated the woofer from bottoming out (and getting seriously distorted).

Now we had a pleasant speaker. But hey, if am going to play speaker designer with equalization, why did I pay the factory $4,000???

Conclusions
ATC is another "PRO" company producing hi-fi speaker. My impression of any such company is that they would produce speakers that would have a neutral and balanced frequency response and hence tonality. I can't fathom how they would produce something like the SCM19. The results are so poor that I am suspecting my measurements must be wrong. But then the listening tests confirmed the same.

I read that the new version uses in-house tweeter. That seems like the wrong problem to try to solve. They should fix the woofer first.

Needless to say, I can not recommend the ATC SCM19 (version 1).

------------
As always, questions, comments, recommendations, etc. are welcome.

Drive nearly 200 miles today to drop off and pick up some gear to test from local members. Last I checked, cars are not free to run so please donate what you can using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

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MZKM

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#3
Amir sent me another set of data in which the microphone was ~10 degrees off vertically (I assume tweeter axis), and the results were thus:

Offset Preference Rating
SCORE: 4.8
SCORE w/ sub: 7.1

Sensitivity: 85dB
Frequency Response: +/-4.7dB 54Hz-80Hz
Screen Shot 2020-07-04 at 12.27.49 AM.png


As expected, the vertical performance is what mostly changed:
Screen Shot 2020-07-04 at 12.27.58 AM.png


Not sure which I should use for my master file, the one ATC recommends (roughly) or what is better.
 
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amirm

amirm

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Thread Starter #4

stunta

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#5
Ouch. ATC provides a long list of artists whose recording studios use their speakers for mastering..Assuming the pro line is similar, our circles of confusion must be well, really confusing if you are listening to those artists through well-measuring speakers.

I've owned the SCM19s for many years and always used them with subwoofers. They sounded good to me until I heard the Revels.

Thank you, @amirm for the review. This is so revealing, it makes me question what I thought was good HiFi.
 

MZKM

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#6
The beam width (how wide the region with close tonality is) on the horizontal axis is on the low side at +- 50 degrees:

ATC specs +/-80 degrees horizontal & +/-10 degrees vertical, my heat map is slightly different in how it colors, and the specs are forgivable:
Screen Shot 2020-07-04 at 12.43.17 AM.png
Screen Shot 2020-07-04 at 12.43.32 AM.png


They also spec that pairs are matched to +/-0.5 dB. Not to many passive speakers have this spec, Ascend Acoustics does for thier higher end models, but they only guarantee +/-1dB matching.
 

Ilkless

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#7
I stand by what I have said about Harbeth, ATC and PMC. The measurements vindicate my view. Clearly ATC has no concept of baffle step compensation.

The British monitor cult of personality is one of the strongest in the industry. They all have a superficial commitment to engineering, yet release merely incremental improvements on rustic designs under an outdated engineering paradigm. Slightly better cone material here, more copper in the motor there. No thought given to the loudspeaker as a system, how to improve the system's radiation, to reduce the total colouration of the system. Just a slavish obsession with big, primitive drivers. The mid dome defeats its own existence.

Somehow people lap up that rustic conservatism. Perhaps because it allows them to point at these incremental improvements to justify their expense despite vastly more advanced designs on the market
The Harbeth playbook, which extends to ATC/PMC with little modification:

It is a laughably backward design. You need an education on the subject. Alan Shaw, like Rob Watts of Chord, is a technically-competent engineer using his skill not to push the frontier, but to defend the hill they choose to die on: handicapping themselves with rationally-indefensible design choices and then being economical with the truth. Let's not conflate that with actual performance, where disproved by empirical evidence. There are a few broad claims to justify Harbeth-style designs by its apologists:

1. Downplaying or wilful ignorance of off-axis behaviour. The SHL5+ linked above shows a massive dispersion mismatch. Many details remain contestable in the vagaries of in-room reproduction. But consistent, smooth dispersion isn't. Pursuing it is consistent with how human hearing functions. To pick Harbeth is to be wilfully ignorant - one could even say anti-intellectual - in the face of this evidence, arrogating that your ears do not function like that of any other human being, claiming that your anecdotal experience supersedes decades of acoustics and auditory research.

What's contestable is how broad this range of smooth dispersion should be, and whether the transition from the optimal range should be smoothly fading or a hard boundary. But Harbeth, in dismally failing even the basic premise of smooth dispersion that precede these legitimate questions, fail to engage them. This article is the first stop to understand why. I have quoted the salient paragraph in my earlier post. It is tremendously intuitive should one step out of the bubble of cognitive dissonance one inhabits in being an apologist for antiquated design. Once this is done, the act of pretending Harbeths to be acoustically state-of-the-art or even high-performance based on anecdotal experience is extremely disingenuous. Peer-reviewed research in authoritative journals have long documented the flaws of anecdotal experience (See Section 3: "Biases in Affective Judgments"). Please don't conflate confounding variables such as the mythology or story Alan Shaw claims with claims of acoustic performance. It is all the more insidious because unlike, say Audio Note, which rely on blatant mysticism, Harbeth's story is superficially evidence-based. It just uses a carefully-curated and cultivated version of outdated evidence from BBC research that has long been superseded, or simply does not address questions such as dispersion behaviour that were not known at the time or beyond their means to properly test.

2. The BBC thin-wall design. Dudley Harwood was an experimental genius. Let's get that out of the way lest one think otherwise. But a thinking man like Harwood would have been acutely aware of hewing closely to his original experimental questions and design requirements. The thin-wall solution was a balanced solution for technology of the time, rugged usecase, budget considerations, ease of manufacturing, portability, and a modicum of experimentally-derived resonance control through relatively-controlled listening tests to help reduce obvious enclosure-related colourations. The frontier has moved a lot since then. In the early 90s, it became possible to directly measure the cabinet radiation independently of the driver radiation (ie. the share of colouration imparted by the cabinet), a technique that Harwood did not have access to. By the 2000s, B&W (which has other flaws unrelated to cabinet design) could use 3D models to accurately simulate enclosure vibration and optimise for it. Similar techniques are in use at KEF, as well as Neumann and Genelec. Before you say it, these techniques are not perfect, but have been refined for so long that we trust it for vastly more critical applications like space travel and ballistics. And the models are unequivocal: smooth edgeless enclosures, achievable only by materials such as cast aluminium or bent ply, are superior on numerous fronts: diffraction, reflection, and cabinet resonance for a start. The sound radiation by the drivers is, in every way, less perturbed. So there cannot be tenable counter-arguments founded on mere anecdotal experience (as apologists like you are wont to wield) against established empirical research and engineering. Again, doing so is anti-intellectual and tremendously arrogant.

3. The Radial2 cone. I've written about it here. Other have also addressed this earlier in the thread. Driver specialists with vastly deeper knowhow and economies of scale specify cone materials regularly. Cone materials they make are now so good that well-optimised cones can roll off without discernable breakup. It stretches credulity to think a small cottage industry without specific knowhow or research capability in the subject can do better. Or that it is truly a proprietary formula of their own making.

4. UK construction. The cost and performance for the price is also defended on grounds of artisanal UK production. Yet sophisticated active monitors packing much more features and using vastly more sophisticated design techniques in similar form factors (eg. Neumann KH120A vs P3ESR) are still being made in the UK/Europe (Neumann: Northern Ireland; Genelec: Finland).

My final note would be that just because a speaker relies on evidence-based engineering doesn't mean that the end product is insipid and uniform and less enjoyable (which is implied in your backhanded compliment of Genelec gear). One enjoys music, not the equipment through which it is transduced. In fact, there is a huge variety of well-engineered designs covering various design formats that comply much better than the likes of Harbeth to what is established, while proposing their own solution to the questions that remain contestable for want of evidence. That these questions remain contestable does not mean that every speaker design, regardless of how backward it is, should be legitimately considered an equal option to well-engineered speakers. It also does not mean that each of these speakers will all sound the same to each other. Different dispersion widths/shapes, bass extension, max SPL, size requirements, intended listening spots, all cause variations.

But they are united in aspiring to smooth dispersion at the very least, which has established effects in:

(1) a broader sweet spot;
(2) more stable, consistent performance across different rooms because we've removed one major variable - significantly different timbre from the speaker at different angles versus the direct sound;
(3) better performance in adverse setup conditions and sub-optimal room treatment. The human ear integrates early reflections into a single auditory event; that is to say, indistinguishable from the direct sound as a discrete echo. However, reflections that greatly differ in sound signature are integrated together and perceived as colouration. A controlled dispersion speaker does not have major aberrant differences between the reflected and direct sound and hence the integration has less colouration to it.
(4) Allow for predictable room treatment. One wouldn't need to fine-tune room treatment to be especially absorptive over the narrow band of mismatch, which requires extensive measurement time to optimise in-room.
(5) Are critical to good imaging. The reason why horizontal directivity is important is because our ears are co-located pretty much on the same horizontal plane. The manner through which stereo generates a reasonable illusion of width, depth and scale is through us receiving input from both speakers into both ears, even when there are not much reflections. For instance: the left ear receives the majority of direct sound from the left speaker, but some from the right speaker, which is displaced to the side relative to the left ear. A directivity mismatch means that the sound from the right speaker has additional dips and peaks that detract from the mechanism we use to generate a "phantom centre" and "soundstage".
View attachment 35433

PMC DB1S-A II detailed measurements. Horrendous mess. And I assume you've already found other measurements from Stereophile that show their bass tuning to be a disaster. PMC is just another one of those antiquated UK cottage-industry brands like Graham, Harbeth, Chartwell, Falcon, Stirling, Spendor and to some extent ATC that produce regressive speakers that (wilfully or otherwise) ignore evidence-based best practices that inform the likes of Genelec. And yet fetishised and romanticised to no end - regarded as equals or even superior to brands that put in the effort to keep up with R&D.
 

pierre

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#9
Ouch. ATC provides a long list of artists whose recording studios use their speakers for mastering..Assuming the pro line is similar, our circles of confusion must be well, really confusing if you are listening to those artists through well-measuring speakers.

I've owned the SCM19s for many years and always used them with subwoofers. They sounded good to me until I heard the Revels.

Thank you, @amirm for the review. This is so revealing, it makes me question what I thought was good HiFi.
Pro as you have seen in this forum are like everybody else. Some tune the studio by ears some use an acoustician and measurements.
To be fair most modern studios have Genelec, Focal, JBLs, Neumann, KII, DD, DynAudio, PSI etc which are very good. There are still plenty
of ATC and PMC but I believe studios would buy something different if they could afford it. They are also very good at learning the room
and how it "translates". This is not complicated in a well done room but hard of course if your freq response is not flat and smooth in room.

Folklore is still running strong in the music production world (Gearslutz is a mix of reasonable comments and pure audiophoolery).

On the opposite side, most recent studios I have visited have excellent acoustics (and yes you can still discuss +/-1dB for days).

P.S.: if someone could send a BareFoot or an Amphion to Amir that would be great. The BareFoot are very expensive, don't have a lot of measurement around and have a good reputation.

PPS: Pro would buy a ATCSCM20 which is +/-2dB on axis. ATC SCM 19 is marketed as a Hifi speaker.
http://atcloudspeakers.co.uk/wp-con...nical-Datasheet-SCM20ASL-Pro-Mk2-revB-WEB.pdf

2cols.jpg
 
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amirm

amirm

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Thread Starter #10
ATC specs +/-80 degrees horizontal & +/-10 degrees vertical, my heat map is slightly different in how it colors, and the specs are forgivable:
With uneven directivity one can more or less draw the line anywhere. :)
 

Beave

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#11
I stand by what I have said about Harbeth, ATC and PMC. The measurements vindicate my view. Clearly ATC has no concept of baffle step compensation.



The Harbeth playbook, which extends to ATC/PMC with little modification:
Agreed - this response looks like insufficient baffle step compensation.

I bet they sound better right up against the wall behind them. I wonder if they were purposely designed for such placement?
 

pierre

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#12
Agreed - this response looks like insufficient baffle step compensation.

I bet they sound better right up against the wall behind them. I wonder if they were purposely designed for such placement?
I don't think so. The large ATC yes but not the bookshelves.
 
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amirm

amirm

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Thread Starter #13
I bet they sound better right up against the wall behind them. I wonder if they were purposely designed for such placement?
Nope. From the manual:
1593839522783.png
 
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amirm

amirm

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Thread Starter #17
Not easy to tell from picture, but the woofer looks like it has some kind of hard/stiff enamel coating. Have you tried to scrape it off if it helps?
??? It is a heavy tar coating of sorts. No way to scrape it off if you wanted.
 

pavuol

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#19
??? It is a heavy tar coating of sorts. No way to scrape it off if you wanted.
just a joke :)

here, some of drivers' tech at one place:
ATC 195mm Super Linear midbass driver - "huge 9kg optimised high-energy magnet system"

Yet, there has to be something about their Pro line. Also worth noting 6Y warranty shared by both their Pro and Hifi line.
 
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BYRTT

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#20
Thousand thanks review and hard work Amir :) sorry sound was low performance and it looks they forgot filter for baffle loss and diffraction :facepalm:...

Sellers_quote_edit.png




BTW here is some synthetic prediction for EQ its listening window smooth as pancake based Amir's spindata:
EQed_500mS.gif
 
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