Acoustic Transducer Company (ATC) has been making drive units and loudspeakers since 1974 and building a fan base in the hi-fi market for the performance quality of its systems for over two decades. Modelled on the company’s Tower series of heavyweight floorstanders, the SE versions bring fancier cabinetwork and electronics to the equation. You pay over 50% more for the impressive finish, inlaid metalwork and all-discrete electronics, but you do get a pretty swanky loudspeaker for your money. And in the case of the SCM100SE, it is a pretty substantial one, tipping the scales at 79kg, over 10kg more than the standard model.
Special Edition design enhancements include nickel piping on top and sides and a matching electro-plated nickel flat plate that covers the amplifier on the rear. On the Classic ATCs the amplifier’s cooling fins and grab handles sit proud of the back, but all of this is hidden on the SE versions, and a second vented panel is fitted to let the heat out. This makes for a more elegant piece of furniture.
Another difference is the plinth that raises the cabinet up a little, creating a gap that adds panache to the design of the speaker footing and possibly helps the bass too. The plinth is threaded on the underside for spiked feet, but I’d be careful about using spikes on some floor finishes given the weight involved. The most satisfying detail of all for me is the curve in the top of the box which forms a ‘brow’ over the baffle housing the drivers. You can choose the colourway for the ‘brow’ section with matching or contrasting fillets, which is a nice touch. The SCM100SE has a rectangular grille with a fairly substantial frame that fits over the baffle. I preferred the look with the grille on, and since the system is tuned by ATC with grille attached, that’s where it stayed for most of my listening.
Like many ATCs the SCM100SE is an active system. There is an electronic crossover and three separate power amplifiers in each cabinet. The signal from a preamplifier goes into the crossover via an XLR-only input, where it is split up using second-order active filters and an all-pass phase correction filter. Then it’s sent to the individual power amplifiers which in turn are connected directly to the drive units. When I asked ATC engineer Ben Lilly to explain the benefits of active operation, he began with the fact that of all the speaker pairs ATC sells into the pro-market every year, less than one per cent are passive, which tells you quite a lot. In a nutshell, the benefits avoid the problems inherent with passive systems. These peccadilloes include the need for an inductor on the bass driver, which absorbs energy, reducing efficiency and compromising the damping factor of the amplifier due to series resistance: similar in effect to a speaker cable. A compromised damping factor means less control over the bass. Another issue is that passive crossovers struggle to cope with the dynamic behaviour of driver impedances; designers are forced to engineer around the problem in order to deliver a least-worst compromise. Then there is the difficulty of achieving a good phase response whilst maintaining an even frequency response and steady impedance. The whole thing is a tricky balancing act. Not only are the most successful passive crossovers more complex and expensive to design than active crossovers, but they also have to deal with the high power of an amplifier. By contrast, active networks receive the far lower voltage output of a preamp.
In an active loudspeaker, the crossover only sees the fixed input impedance of the power amplifier(s), which in turn have low output impedances and can cope with the variations presented by any driver, especially when they’re specifically trimmed for the job. Thus the optimised power system aboard the SCM100SE has a 50W amp for the tweeter, 100W for the mid and 200W for the bass driver.