By design, an ESL is a very linear transducer. The voltages across its two stators are linear within the space between them. In electrodynamic drivers, the small space in which the coil moves inside the magnetic structure makes it hard to be linear just like the fields generated by the voice coil are not linear. The pushing and pulling action of the magnetic motor on the voice coil relies on the coil’s constantly changing position with regard to the magnet. With an ESL, the pushing and pulling of the membrane is linear across the complete diaphragm and the force applies evenly over the entire surface. Where dynamic drivers can and will suffer from break-ups as the cone is not always able to follow the coil movement exactly and oscillates, an ESL follows the input flawlessly (unless overloaded of course). Most dynamic drivers are housed in a cabinet which adds colourations and is always a compromise. ESLs don’t come with cabinets, hence don’t suffer their effects.

As already mentioned, the polarizing voltage on the diaphragm must be applied by plugging the ESL into the wall. Placement in the room is another aspect that needs to be addressed carefully. An ESL is a dipole radiator which means the back of the loudspeaker emits just as much out-of phase energy as the front but very little sideways. Placement too close to the front wall does not work well but a spot in close proximity to a side wall is no problem. On that same placement topic, ESLs with a few exceptions show limited horizontal dispersion. This means their sweet spot is quite narrow. Likewise, vertical dispersion is critical when looking for the best placement. Experimenting with tilting the loudspeaker forward or back to match the listener’s ear height is essential.

ESLs are also demanding of the amplifier/s they are combined with. Sensitivity is not an ESL forte so a power amplifier capable of delivering sufficient voltage is necessary. That amplifier also needs to be able to handle a very reactive load. Impedance can dive dramatically as frequencies rise. Swinging down to 2Ω or 1Ω from a nominal 8Ω is no rarity. And in general an ESL does not play very loud, does not go very low and does not blow the creases out of your pants. That’s in general as we will see.    

Against this general background, we received an e-mail with a question: were we interested in reviewing a new crossoverless full-range electrostatic loudspeaker? Hola, wait a minute. Crossoverless and full range had to mean no added dynamic woofer, i.e. one huge room divider. Visions of immense Soundlab electrostatic speakers popped up. Admittedly our listening room is not small but really huge ESLs? Fortunately the e-mail pointed us at the website of the manufacturer, Soltanus Acoustics of Serbia. There were the dimensions: 153cm tall, 68cm wide with a depth of 5cm at the top and 33cm at the bottom. These dimensions were roughly the same as the Quad ESL 2905 we auditioned some time ago and still had fond memories of. Christened ESL Virtuoso, the review offer was tempting and we agreed to take it on. Arrangements with designer and owner Zoltan Mikovity in Subotica/Serbia were made who insisted to deliver them personally. At the agreed date and time, a white van with Serbian plates pulled up. After a night in a hotel, Zoltan and companion Milo who came along to help felt refreshed after their 1’500km long journey. In the early morning sun two flat wooden crates emerged from their van. With a modest weight of 26kg, the Virtuoso loudspeakers are easy to manhandle once released from their wooden confinements. Assembling them is down to attaching the Y-shaped steel bottom plate and affixing two self-adhesive steel spikes in the front. The third spike is part of the steel plate and equipped with a long thread, enabling the Virtuoso to be raked forward and back for precise setup.

Before Zoltan arrived, we had moved our resident Pnoe horns to make room for the Virtuoso. We agreed on setting them up 2.8m center to center and 1.7m into the room. The sweet spot with this initial setup was at 3.9m from the front line. Moving the speakers around was easy but a second person is needed to put protective footers under the spikes and shield a wooden floor. A modest toe-in aimed the center of the speakers at the sweet spot. Hooking up the ESL Virtuoso proved straightforward. At the lower back of each speaker sits a panel with an  IEC power inlet, two knobs and three (!) 5-way speaker binding posts. One binding post is for the return, the other two are for either a power amplifier with a damping factor 25 or less: or an amplifier with higher damping (lower output impedance). The two rotary knobs are to fine-tune the match with amplifiers of a low damping factor; and to adjust tweeter bias. Amplifier damping factors of 1-2, 3-4, 6-12 or 12-25 are selectable in combination with the binding post for a low damping factor. With the other selector, the tweeter’s bias can be tailored from -3 to +2 in accordance with the room’s absorptive/reflective behaviour.

All our amplifiers fit the high-damping figure to determine the matching connection. Zoltan wanted to make sure the speakers were in perfect condition so a preliminary connection with the review sample Abyssound ASX-2000 power amplifier was made using a pair of unbranded cables Zoltan had brought with him. Satisfied with the workings and initial setup, the two Serbs left. Because the Virtuoso were not fully broken in yet, we detached the AbysSound and connected a Devialet D-Premier with two lengths of Crystal Cable Crystal Speak. That’s because the Devialet has a built-in brown noise generator. Brown noise is ideal for burning in lower-frequency drivers since its energy distribution is mainly in the lowest frequencies. Each octave contains as much energy as the two octaves above it. The bandwidth between 20Hz and 40Hz (one octave) offers the same sound power as 40Hz to 160Hz (the next two octaves and so forth). We let the brown noise softly run for two days after which we played real music just for background levels and more softly overnight as an endless-repeat loop.