purist ESL MK2

Setup HighEnd2012, Munic
Setup HighEnd2012, Munic

From the experinces with the ESL-Prototype the following requirements arose:  

  • optically more pleasing and more compact appearance
  • support by a dedicated active Subwoofer

Gallery (click to zoom)

 

Bass tower and base plate front, CAD
Bass tower and base plate front, CAD

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 drossectional area of the tower has become even smaller.

Detail view backside, CAD
Detail view backside, CAD

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

Detail top brace, CAD
Detail top brace, CAD

The ESL-panel is framed by very thin aluminum profiles. A horizontal brace stabilizes the structure along the panels top edge.

 

Base plate floorside, CAD
Base plate floorside, CAD

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.

 

Detail base plate, CAD
Detail base plate, CAD

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.

Subwoofer 750
Subwoofer 750

The pic shows the related subwoofer.

The casing is monolithically cast from concrete as a 30" diameter global form. Two 15" driverrs 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.

 

15" Subwoofer driver
15" Subwoofer driver

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 the tinyist signals easily and precisely.

 

15"er moving parts
15"er moving parts

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 electronic crossover and the Subwoofer-amplifier with its own digital X-over.

The electronic crossover works with filters build from discrete parts under useage of JFET-transitors. Negative feedback (NFB) is omitted with apart from where its needed for the generation of the filter response.

The music signal runs 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.