That article was an interesting snippet for me, especially as I am fettling a Garrard 301 turntable my dad gave me years ago.
The article contains a quote
This is where we think the original designers, Peter Walker and D.T. Williamson, might have ended up as an ultimate statement product
I beg to differ. Peter Walker knew the limitations of the original ESL, now known as the 57, and six years after its introduction started work on a completely new design, the ESL-63 which was finally released into production about 18 years later. The ESL-63 has evolved through a few models up to the ESL-2912X released some weeks ago. Not bad for a 60 year old design!
Major changes included: flat panels, not curved; integral dust covers; incipient ionization detection; protection from high input voltage; far kinder impedance characteristics; oriented for stereo not mono playback.
By far the biggest difference, and something that still differentiates from all other panel speakers, is the creation of a virtual point-source of sound about 1-ft behind the panel. To visualise this, imagine a sound wave radiating from such a source. The wave first intersects the centre of the panel, then expands outwards in a circular pattern. Pater Walker's design creates eight concentric stators which approximate rings. The signal to the outer rings is delayed according to the speed of sound to give the uncanny effect that the sound is coming from1-ft behind the speaker.
The result is that the sound is almost perfectly coherent, allowing the ear-brain to perceive a huge soundstage even in the presence of wall, ceiling and floor reflections. By contrast, the ESL-57 has a very small sweet spot!