From the experinces with the ESL-Prototype the following requirements arose:
Gallery (click to zoom)
The first requirement could be realized with useage of smaller sized drivers and the omittance of the electronic casing below the electrostatic panel. Now the height of the panel dictated the overall height of the ESL. The Bass tower is equipped with 8pcs of 6.5" drivers. The front is curved and the drivers are mounted from the inside. Such results a clean design without any visible screws. With a width of 8.3" and a depth of 7.1" the crossectional area of the tower has become even smaller.
A cutout in the base plate right below the basstower provides for just enough room for the electronics subassemblies. The Subassemblies are the audio transformer with variable resistors, the HV-supply and a supply for the logo-lighting
The ESL-panel is framed by very thin aluminum profiles. A horizontal brace stabilizes the structure along the panels top edge.
Routed from massive aluminum the base-plate embraces the contour of the panel and the tower with lighthearted swing. A beam to the backside leads a height-variable foot. The electronics is contained in a cut-out of the base plate below the bass tower.
Even though of an effective width of ~28" and a height of ~63" the transparent panel makes the systems visual impact mauch smaller.
The electronic circuitry is supplied with power via the active crossover LMS.
The pic shows the related subwoofer.
The casing is monolithically cast from concrete in a 30" diameter global shape. Two 15" drivers are mounted to the cutouts on each side of the globe. Their parameters are optimized for mounting in small closed cabinets. They can perform huge linear strokes of up to 2.4"
The global shape of the casing is mechnaically extremely rigid and free of resonances. The nechanical impulses of the opposing bass drivers compensate for each other. Even under the most extreme excursion conditions the casing remains absolutely dead.
In such a casing the drivers can really shine and perform at their best.
Typically you find similar looking drivers among car-hifi stuff.
Unfortunately those drivers are equiped with very stiff and lossy moving parts, which require to push the driver with a couple of hundreds of watts before it recognizes that music knocked at its front door.
Not so with the used drivers, that feature smooth-running suspensions that follow tinyist signals easily and precisely.
To cope with high power levels the suspensions progressively becomes stiffer. A non-linear winding of the voicecoil supplies for increasing force with increasing excursion levels. This keeps the driving force, BL-factor linear and high. The BL sinks to 70% at +-1.2". This guarantees high dynamic performance down to the infrasonic range.
The system is completed by the active analog electronic crossover and the Subwoofer-amplifier with its own digital X-over. The electronic crossover works with filters built from discrete parts under useage of JFET-transistors. Negative feedback (NFB) is omitted with apart from where its needed for the generation of the filter response. The music signal passes only through a low number count of active parts. The Xover puts a low frequency limit to the working frequency range. The Bass crosses over to the ESL at 180Hz. The Subwoofer-amplifier consists of two class-D amplifiers, each putting out up to 1.500W of power. A integrated digital crossover feeds the amps with a filtered signal (16Hz to 50Hz) and allows for extensive room customization.
update: The owner of the ESL, Mr. Milkovits, constantly tried to improve the already exceptionally good acoustic results. We both knew from an early stage on that a step forward could ly in the use of a digital loudspeaker management system. As the results with the smaller prototype showed, a simple digital IIR filter was clearly inferior to the analog xover. We had at an very early stage also run a lot of tests with a flagship FIR filter system from 4audio. Though the resulting curves and test signals were almost as perfect as textbook sketches, the analog filtered system still sounded superior -under acoustically non-critical room situations that is. Since the development of our own DACs we had the strong guess that the analog periphery of the ADCs and DACs in those management systems were the real bottleneck, even if it were technically perfect textbook designs.
The analog xover still sounded more lifelike and believeable.
Fortunately with Accourate there´s a software that allows for room correction and filtering just like with the 4audio or a DEXQ et al. Our music servers have way more than enough calculating power left to handle the digital filtering. So there´s only a large enough number of 1st class DACs required. Running Accourate only in 2-channel mode as a overall corrective on the server, still utilizing the existing analog setup, already improved the acoustical outcome. Most prominent the bass and lower mids gained and the general impression was of a bit more refinement in precision and staging.
When the system was finally upgraded with multi-channel DACs to an all-digital one, there was a clearly noticeable sonic improvement. One thought that the niveau was so incredibly high already, that one couldn´t imagine any improvement possible.... but the heck, its there, obvious and clearly audible. So the journey continues ...