ATC SCM50 measured performance vs. high quality studio monitors

Hi Folks,

No doubt many will remember the ATC Speaker meta thread a while back (I believe it's still alive, can someone go and put it out of it's misery?).

In this thread I contended that contrary to ATC's advertising their speakers where not the most accurate monitors available, in fact I contented that where other Monitors available that could easily lay claim to greater degrees of accuracy in the traditional sense.

I listed specifically poorely controlled directivity, lack of time alignment and pulse fidelity, high levels of distortion and compression, compared to state of the art Studio Monitors as being points against ATC's products.

Those who insistent on the literal truth of anything having descended from upon high via the High Priests of the cult of ATC and the Marketing Gurus of ATC took exception to my complaints and the lack of actual published measurements and formal specifications as well as the misleading way certain actually specified items where stated by ATC allowed no conclusive proof or rejection of my contentions.

Luckily the current HiFi News carries the measurements of ATC's SCM50, including distortion and a reasonable number of off-axis curves, so we can at least judge the ATC on frequency response, dispersion control and distortion against some of those I claim as State of the Art. Sadly neither impulse response, water fall or compression measurements where published, making any comment on how the SCM50 fares in this department as of now impossible to substantiate with measurements.

For an SPL equivalent to 90db/1m the SCM showed around 0.5% 2nd HD at 100hz and without curves shown list the midrange & treble distortion as < 1%. The curves shown are bob-ideal to judge distortion and require carefull interpretation but suggest MORE than 1% THD for most of the midrange/treble.

Now it is much more common to measure the distortion for an SPL of 96db/1m or as the NRC in canada often does. Looking at the MEG RL901K (http://www.me-geithain.de/) we find the following typhical specification for 96db/1m, that is at an SPL considerably higher than the 90db found for the SCM50:



We observe halve the distortion of the SCM50 @ 100Hz at 6db more SPL and a midrange-treble distortion that also remains more or less flat at around 0.25%, so mostly 1/4 of what the SCM50 manages for 6db less spl.

In fact, while reviewer of the SCM50 calls his distortion measurements "remarkably low distortion", I would call the performance of the SCM50 on distortion REMARKABLY POOR, when compared to state of the art studio monitors.

Secondly, looking at the overall frequency response we find two notable depressions for the SCM50 in the crossover regions leading to a broad depression around 500Hz and a deeper amore pronounced suckout around 4.5KHz, these trends in the on axis response will have definite sonic results and are clear and drastic deviation from neutrality. Further, low frequency rolloff is notable at 40Hz and below.

If we compare the MEG RL901K:



Here we find indeed an accuratly balanced response, with no obviously depressed or boosted areas, giving reliably a netral tonal balance, not one tailored towards a certain sound.

Looking at the measurement above we also note the 45 degree off axis measurement which first off all shows a material attenuation compared to the on axis response above 250Hz (indicating good dispersion control and at 45 degrees off axis above 250Hz a response still fitting a 5db wide window with no obvious trend to high frequency rolloff up to around 15KHz plus, one would like to see better dispersion control below 250Hz as well, byt that arguably becomes difficult.

Comparing this to the off and on axis response graphs measured for the SCM50 we find no systematic off axis attenuation up to around 4KHz and then a fairly rapid high frequency rolloff already reaching 5db at 10KHz for 30 degrees off axis. In addition the off axis response becomes progressively more uneven as the angle increases which together with the already substantially non-flat response throught the midrange must make the off axis reponse quite substantially coloured, a direct result of the complete failure to address dispersion control whatsoever.

All in all the measurements HiFi News took for the SCM50 are indicative of a performance no better lower mid-fi equipment and certainly dramatically worse than anythging remotely acceptable for a high quality studio monitor. In fact, I am shocked at just HOW BAD they are, a pair of 1970's Tannoy monitor gold will provide imeasurably superior objective
measurements.

All that said I do also think I can discern the patterns to a good degree that cause my own complaints about the subjective sound quality of the larger ATC speakers (note they all share fundamentally identical midrange & treble units, crossover approaches and amplification, only LF performance varies), one is smugly satisfied that one indeed did hear what one thought one did.

Ciao T

 

People I dont think anyone wants another ATC slanging match...

so please if you're going to contribute to a thread on the measurements of ATC speakers vs other studio monitors, please stay ON THAT TOPIC.

You know it makes sense.


Cheers!
Chris

 

Speakers are notoriously difficult to measure. You (I assume) are aware of the work of Floyd Toole on measuring speakers and the lengths that he and his research team go to to measure the speaker as a whole - and you're probably aware of the collosal investment in the test equipment, which includes a world class anechoic chamber.

I say this because HiFi News is unlikely to have access to such elaborate test facilities. We can argue about the validity of any tests that they have made in psuedo anechoic conditions (including windowing the impulse response) and close proximity bass measurements etc. and the value of those compared to what might be acheived in a proper test facility.

I'll also point out that the MEG data is from MEG's website.

It would be interesting to see the HiFi News data for the MEG's - if such exists - so that there is a "level playing field" as far as testing conditions exists. I could claim 0.5% THD in their test gear for the sake of argument

Likewise, it would be interesting to see ATC's data, although they haven't put it on their website, for comparison with what the marketing dept at MEG are putting out

It's nice to see a subjectivist (like your self) quoting "measurements" - I was under the impression that people in your camp thought that all such data was meaningless.

The MEG's look like interesting speakers - the stands alone will give bub apoplexy, and that's good enough for me

 

I like the fact that the stands allow the speakers to be angled. Im sure Castors are very useful from a studio point of view, but wonder if spikes might be better soundwise.

I cant comment on the statistics printed, as really I only have basic understanding of these type of graphs.

Thorsten, have you contacted ATC to get copies of their own statistics? That seemed like a fair question to me. Im sure they must have them.

 

Hi,

They used to be. Conventional Speaker measurements (eg anechonic response, Implulse response, THD etc) can be made very easily (I can do it with excellent accuracy using a calibrated measurement microphone, mike preamp and laptop PC).

One may argue (and I normally do) that these conventional measurements do not have any direct bearing on percieved sound quality, however there are some "KPI's" (Key Performance Indicators) that can be derived from traditional measurements.

Yes, I am quite familiar with Dr. Toole.

The interesting thing is that if you substitute groundplane measurements in the open you can get accurate LF measurements without an anechonic chamber (we used the same trick in the 80's in east germany to make up for the lack of an AEC). With gated MLSSA measurements in open air you get a very accurate result fro midrange and treble.

The results match those of large anechonic chambers quite well, well enough to be considered as "within sample variation and experimental error".

Just because HFN do not have big AEC does not mean the cannot produce meaningful or acurate measurements.

Yes, and this would normally not be considered trustworthy, but rest assured that due to the specific system present in German staterun radio for equipment procurement what MEG claim to be the measurements are what they claim.

As MEG is strictly a "Pro Audio" manufacturer they do not bother with the HiFi Market. You can see independent tests in a number of german pro audio magazines, in the US and the rest of Europe MEG has only recently been interest to market their products at all, they used to stick strictly to the german domestic market.

It would be very interesting indeed. And given that hard data on traditional KPI's is usually available as a matter of course, it is particulary interesting that ATC avoid to do so. I generally find this in the Pro-Audio arena only with manufacturers who feel presenting such data would not give them any advantage in competition as the looks questionable, compared to the competition.

First I consider myself an Objectivist, but one whose understanding of what humans hear, as opposed to instruments is a bit more three-dimensional than with most engineers. As a result I do not consider THD&N Measurements as such an indicator of quality or merit (they do still tell me a thing or two though) or on axis anechonic frequency measurements an indicator of quality or merit and so on.

Hence my insistence on the merit of a clean implulse response and of the merit of controlled directivity, both of these are significantly more important and given the magnitude of distortion in speakers (MEG around 0.25% for -20db of stated MOL [Maximum Output Level] and ATC around 1% for -22db of stated MOL) compare to even the most distorted Amplifier (SE Zero Feedback Valve) of distortion as being the KPI's in Speakers at least as important as on axis FR if not substantiatively greater.

What I find funny is that ATC not only shows bad measurements for the non-conventional but highly important parameters, but even classic on axis FR is not at all good, with distinct and broad depressions or boosts (depending how you view this) in the frequency response amounting to around 6db which will result in seriously audible deviations from neutrality (by companrison, a narrowband anomaly of as much as 12db depression is often completely inaudible, even in the most sensitive range of the ear..

They are very interesting. I encountered their original version (which was slightly different to the current one) in the late 80's in studio's in east germany and I felt then and there that here was a major advancement in sound quality over the previously available monitors (mostly 2-Way 12" Coaxials the legendary TH315). It got me into a long time of playing with active speakers eventually all the way to Motional Feedback, I ended up in a different corner to MEG and later returned to passive/fullrange systems, but that is personal preference.

The MEG's remain totally awsome in their own right.

I find interesting that good impulse response, flat frequency response and so on are attained strictly using analogue circuitry, no digital delay to time align drivers, no digital EQ and XO, all the same basic analogue technology originally developed in the mid 1980's!!! And it is still state of the art 20 Years later!!!

As to the stand, the guy behind MEG is violently "anti-tweak" and "anti-audiophile" (one of the reasons that MEG has stuck to "Pro-Only" for so long), but the same style stand has been east german tradition for ages, the argument being that depending on what material you mix/monitor you may wish to re-adjust the monitor position from one close to mixing desk to a more farfield one and of course that the monitor must be raised to ear hight. I agree with bottleneck though, spiking the stand will likely get a notable change in sound, maybe an improvement (maybe not, as speakers and stands are designed together).



Yes, flies so much into the face of percieved and traditional wisdom in Pro and Consumer audio than one cannot but love the Chuzpah of Mr. Kiesner.

I'm right now working with friends on a shameless knockoff (unlikely to become commercially available I'm afraid, maybe we will release the plans at some time) but using an Audax PR-170M0 midrange, Aurum Cantus Ribbon Tweeter and commercial 15" Woofer and most critically a minimalist (series) passive crossover (as we want a PASSIVE speaker with utmost neutrality and transparency to evalute amplifier sonics).

So it will quite dissimilar to MEG, but should be interesting too, here a conceptual 3d rendering....



Ciao T

 

Hi,

Actually, they are NOT PORTED, at least not in the traditional sense. The "ports" are the exits of an acoustic delay line which is used to produce a cardiodic charateristic in the low frequencies and attenuates the rear output at low frequencies by about 10db from 30Hz - 80Hz and with 18db attenuation at 100Hz.

See here:



And here:



There is a pretty lengthy paper posted about that on MEG's website, this "K" Technology is the only really new thing in these speakers in the last 20 Years!

It is about the only speaker I know that has decent LF directivity except dipoles (note that MEG uses a dipole/open baffle midrange!) and monster horns, oh yes, there was one company, Meyer I think that now makes directional bass bins.

Around 15,000 Euro the pair, AFAIK, UK pricing may vary thanks to rip-off britain. You do get a total of 380W on board Amplification though and the bragging rights of "my Woofer is bigger than yours" over all ATC owners except SCM150 & 300 and all PMC Owners short of the BB5.

Ciao T

 

I am appalled, nay rocked to my very foundations by these latest revelations from Mr Fruitcake. How do ATC get away with it? I think we should be told.

 

Yes, but are you familiar with Dr Toole's tool? It's a formidable weapon, or so I'm told.

 

Really we need to consider speakers, stands and flooring together. The effects of spikes can be very different on concrete floors compared with suspended wooden floors.

PS: T, what did you think of motional feedback?

 

Hi,

After I had it finally going well it did well, I managed at normal music levels to get a pair of fairly generic 8" woofers to pull level with the custom 15" in the older MEG's (which used no such trickery) but once the system reaches the limits it overloads quickly and nastily.

The bottom line is that NFB of any type cannot really help gettingsomething the system without NFB cannot do anyway (and motional feedback is NFB).

Ciao T

 

Presumably NFB is -ve feedback. I wouldn't generally use it but I would certainly consider -ve feedback for the bass. In my systems the bass driver only plays up to 200Hz. OK, it gets nasty when the limit is reached but I would live with that. It interests me.

Is it difficult to implement, can I get the accelerometers easily and do you know if patents still apply?

PS: I should also ask what MFB does that equalisation doesn't.

 

Hi,

There are a number of approaches. I originally started with the feedback signal derived from the voicecoil, this prooved both non-linear and instable.

I later used electret microphone capsulas similar to what Meyer now does, this worked quite well, but had limits, once the system was driven far enough to overload (given only 2 pcs 8" drivers per side not actually that insanely loud) and the NFB unlocked distortion was gross and on occasion drivers blew out. That lead me to add a limiter system derived from pro-audio "processor pa" applications, using both an excursion based limiting system and one based on RMS thermal power. I also upped the amplifier power a lot, so that any signal that does not damage the driver can get through unclipped.

The results of all of that where good enough, but a large size pro woofer simply has a better overall dynamic range, NFB can linearise the smaller speaker while near the limits, where normally sound quality would already suffer, but it cannot make a speaker exceed physical limits. As such it has uses, but I never really got back to it.

MFB is literally traditional NFB which includes the speaker in the loop. It was invented by German Engineer P.G.A. Voight in (IIRC) 1922 and predates Blacks more traditional NFB patents by more than a decade.

As MFB in effect compared the "is" cone position with the "should be " cone position and issues a compensation signal is the two diverge it addresses both distortion and frequency response, as well as compression. EQ cannot address either distortion or compression.

Ciao T

 

Interesting post - I would very much like to see a comparison of ATC and MEG speakers (and others for that matter) done by an independent party (the same for both), with the same measurements under the same conditions. I don't like comparing measurements from two very different sources under [potentially] very different conditions - especially when one source stands to gain an awful lot from good results!

One thing I would like to mention, which comes partly from personal experience - AFAIK ATCs aren't meant to be listened to on-axis, and they sound clearly "wrong" this way. They should be pointed straight out with (IMO) a smallish amount of toe-in to taste. I'm experimenting at the moment with them angled sharply inwards (crossing in front of the listener) and obtaining excellent results as it drastically reduces room effects and ensures rock-solid imaging. But in any case, on-axis is a no-no, and you can see in the HFN measurements that the FR is much smoother a few degrees off-axis.

Dunc

 

Hi,

Hmmm, again something unacceptable for an accurate studio monitor, as several people may be listening over a certain area.

In order to get this to work well it is neccesary to have notable toe in (in fact the standardised 60 degrees equilateral triangle when use with sufficiently directional speakers will do that well) and to have the "hot-seat" more or less on axis with seats to either side receiving an attenuated output from the closer speaker to keep any stereo imaging possible.

Now for a single person listening home audio system anything that people like goes, even Bose....

Yes I noted this, I also note that even the smoothest curves are fairly non-flat over significant ranges.

There is a good acoustic reason why this helps a lot. Again, setting up the speakers like that, when you move to one side you get further off axis where you already are while moving more on axis for the speaker further away from you. This tends to level out the differences in SPL.

Ciao T

PS, I am also all for an independent test, of both subjective performance and objective performance, especially with the inclusion of extensive off-axis response measurements all the way to 90 degrees, impulse response, distortion and compression.

 

I've put a few dots on mine - to great effect.

 

If we're looking at measured frequency response as a significant (but not sole) indicator of accuracy then what is the deviation for the SCM50 across its frequency range?

The flattest claimed response I've seen is for a pair of Mackie HR824 at +/-1.5db 39Hz to 22.5kHz. Is it possible, within reason, to engineer flatter than this?

Further is chasing a flat frequency response a worthwhile pursuit for domestic listening unless you pay the same amount of attention to the room acoustic - re-building from the floor up with mineral wool loaded walls and floating floors etc?

 

Mr 3D Fruitcake, have you taken your ideas to ATC? There's little point in whinging about their speakers here - we are unable to stop the misery which ATC inflict on their users worldwide.

 

Hi,

First, the plots in HFN are heavily smoothed, some of the deviation depends on the choice of reference.

If in the HFN plot (should be in fig one but is swapped with fig4) we set the reference to 90db, we find a 1db peak at 100Hz and10KHz and a depression to the tune of at least 4db in the 500-600Hz region, this is a fairly broad depression betwwen 200Hz and 1KHz. We also find a 5db+ dropout at 4.5KHz, a combination of a broad depression and a deep narrower suckout.

So, on that basis we could suggest that the SCM50 Manages +1/-5db between 100Hz and 10KHz with -6d points at40Hz and above 20KHz, on axis only.

I suspect it is, however as noted before, narrowband deviations worry me little, as long as an overall balanced response is retained. However, clearly, if Mackies claims where to be born out, Mackie Monitors would have to be counted as considerably more accurate than ATC.

No, I do not feel that persuing a flat frequency response, on axis, anechonic, as such is relevant, but that an evenly balanced sound output, in room, at the listening position is, as well as a pulse coherent first arrival and low levels of distortion are.

Ciao T

 

Hi,

My comments are aimed at providing (late, but better late than never) backup that can be actually assesed and which IIRC you demanded as to my objections that "ATC makes the most accurate studio monitors available".

I would consider my point well proven, at least for the SCM50, it's measured perfomance is well below the AVERAGE standards expected from a serious studio monitor.

Of course at home you may listen to whatever you like, with my blessings, no accounting for taste. Just avoid calling ATC speakers "accurate" please.

Ciao T