E-scale is simply an evolution of the multiscale concept.
E is for ergonomic and the exponential formula used to determine scale lengths.
“In 2011, after building and playing multiscales for 6 or 7 years, I started looking more at their benefits and limitations. The areas where conventional parallel frets were superior, and how the best aspects of standard multiscale could somehow blend into that traditional and familiar feel. The second octave (12th fret upwards) was my primary concern as the human wrist doesn’t naturally bend in towards the body. If I could somehow make the treble side above the 12th feel like parallel frets but keep the tonal and ergonomic improvements of increasing the bass side’s scale length.
The solution was to gradually increase the scale length difference from string to string working from treble to bass, retaining the outer string scale lengths and positions from my original standard multiscale designs. As a result the frets end up curved, as does the front edge of the nut and the bridge saddle locations. The nut to 12th area of the neck feels much like a conventional multiscale, the 12th fret upward is closer to parallel fretted, and the bridge follows a natural flowing curve I find more comfortable than a simple angled straight line.
At that point I abandoned all other designs to concentrate on refining the e-scale 7 and 8 string build processes. The 6 string followed a few years later and that design became known as Essi in 2018 after I started looking seriously at building other models again. The e-scale frets are fundamental to the Essi design but no longer exclusive to it. The A-type and Brute can be built with e-scale, and it will find itself on special one-off pieces as well. ” – Dan, Oni Guitars