active better than passive?

One does not know exactly why. But ATC, that wonderfully English loudspeaker company, sails far too far under the radar, at least in the hi-fi sector. It is common knowledge among connoisseurs that ATC has been building breathtakingly good sounding loudspeakers for almost 40 years. It is not for nothing that they are used in so many well-known studios - from Abbey Road to Sony Music Studios. So we go in search of clues. And with a loudspeaker that stands for the essence of this traditional British company like no other: The ATC SCM 50 ASL has of course always been updated, but it dates from 1985. We had the evergreen in the listening room for a few months. Result: The concept from back then can easily compete with the most modern and popular speakers.

Stroud in Gloucestershire. Here in the far west of Britain, where everything looks like something out of an Inspector Barnaby episode, where the sea (which is called the Celtic Sea) isn't far away and there's never a hint of hustle and bustle anywhere, this is where Acoustic Transducer produces and develops Company, or ATC for short, has been making loudspeakers for four decades. Such an environment naturally rubs off on the products...

Last fall I had the opportunity to visit the company. More than 40 people are employed here, all with heart and soul. If you talk to the people in production or shipping, you can feel their spirit, the conviction that they are part of something extraordinary.

ATC does make exceptional products. The vertical range of manufacture of the British is enormous. The legendary drivers such as the 75 mm SM75-150S midrange dome are all lovingly handcrafted here. The coils are wound in-house and the driver magnets are magnetized on site. And behind each station there is a test point where the individual steps are checked again. The ATC quality standards are very high - not only measured by the British level.

ATC founder, Billy Woodman, also stopped by for a brief time during my visit. Woodman, actually retired, is a real believer and still brims with enthusiasm. I grabbed the opportunity and asked him what makes the ATC speakers so special. Answer Woodman: “Low-distortion drivers and the most perfect phasing possible. With it I not only achieve a clean takeover between the drivers, but also ensure absolutely controlled radiation behavior in the vertical plane.” He's probably right, because the ATC speakers always sound extraordinarily clean.

And yet the hi-fi people are rarely euphoric. If you ask at trade fairs or dealers why the fans are still so reluctant to talk about ATC, the nasty word "ugly" is often used. But please: ATC speakers aren't ugly, they might be peculiar. They follow a robust, functional design, there is no room for unnecessary ornamentation. That shows character.

And that will probably remain the case – as the following episode shows. After lunch, a tour of the production facility and intensive discussions about the pros and cons of the ATC ideals, we went to the bar in the evening. After a few (of course much too warm) pints of beer, I plucked up courage and said: “You already know that yours Loudspeakers aren't considered particularly pretty?” “Of course,” I said happily. "So stay tuned to see what happens tomorrow."

The next morning we arrived in a room where a loudspeaker was covered Christo-like with velvet cloths. There was a strict ban on cameras and mobile phones. The velvet cloths were removed - and there was a completely normal ATC speaker. Particularly keen eyes might have spotted one or the other curve. Otherwise the usual, not a trace of "design". I really had to laugh and was somehow also happy – everything else wouldn't have been ATC.

The structure of the ATC SCM 50 ASL

Accordingly, the oldest, still up-to-date ATC looks like an ATC should look like: angular, straight and kept in exactly the medium size that was popular at the time - too small to put it on the floor, too big for you correct stand. I personally find this monitor look sexy. And as you can see from the Yamaha NS-5000 , for example , it's coming back into fashion.


The weight of the ATC SCM 50 ASL was a bit surprising for me. When asked by colleague Jürgen Schröder whether he could help me unpack, I initially rejected the question: I'll do such a small thing on my own after all...

I couldn't. The compact 3-way combination weighs a good 50 kilos and I timidly had to ask for help because it is also so difficult to handle. Colleague Schröder was also amazed: "Yes, is it filled with lead? Where is the weight coming from?

First of all, the extremely solidly constructed housing with multiple internal struts. If you knock on the walls, the quality becomes audible or inaudible: nothing vibrates.


Then there is the metal connection plate, on which the three power amplifiers and the components for the active crossover find their place. The crossover is steep (24 dB per octave) and the output stages are three times the same (analogue) type in AB circuit. However, the three are designed differently in terms of their output power: 50 watts for the treble, 100 for the midrange and the power-hungry bass range is supplied with 200 watts. All three output stages are connected to the large transformer, which, together with the power supply capacitors, ensures the appropriate stability.


The discussion with the ATC people about their power amplifiers is always interesting. Because here the work is actually done with little effort and by no means the latest technology: The driver function is taken over by an operational amplifier 5534, further voltage and current amplification is provided by the four MOSFET power transistors. Despite (or because of that?) the result is first class. So don't nag.

However, the three drivers have the largest share of the weight. The 25cm bass in particular boasts a weight in the double-digit kilo range. However, it's not about as much weight as possible, but about the least distortion and maximum neutrality. And indeed, the drivers from the Acoustic Transducer Company are of the very best quality. Thanks to hundreds of Klippel simulations, they are absolutely top in terms of impulse behavior and low distortion.

The almost huge mid-range dome with a diameter of 75mm has to be singled out. Billy Woodman brought the thing to market in 1976. Since then, this exception driver has been refined again and again. Today it is - as the measurements show - wonderfully low in distortion and can be used from 400 Hertz to well over 4,000 Hertz.

In terms of bandwidth, it is hardly inferior to today's popular cone midrange speakers. Its advantage is the wide and homogeneous radiation, which usually leads to a very light and airy reproduction. Anyone who has ever heard an ATC with the large dome will agree: it sounds incredibly transparent. The homogeneous radiation in the horizontal plane is probably one of the most important building blocks for this airy reproduction.


Compared to the woofer and midrange, the tweeter is a real novelty. The driver with the low-resonance fabric dome is only a few years old and has been optimized for the combination with the midrange driver, also in terms of radiation. You can hear that: the two domes sound as if they were made of one piece.

Measurements & practice

First the connection. According to ATC, XLR access is absolutely sufficient; one thinks nothing of asymmetrical supply lines. Basically, the approach is correct, because active loudspeakers are almost always connected to the preamplifier with long cables, which then harbors the risk of interference and ground loops. Long-distance interference can be dealt with well using XLR cables. Especially since ATC also adjusts the XLR input manually for maximum freedom from interference. In this way, the British achieve broadband common-mode rejection of at least 70 decibels. Normal, unbalanced, balanced inputs hardly exceed 45 decibels.

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