I have a pair of Stax Lamda Signatures and an "original" energiser, srm-xr from the 80's I imagine. The headset looks identical and the only change they made in later models is to use a thinner membrane for more efficiency and extended "delicate" hf. Always been "state of art" as an electrostatic design enjoying all the performance expected of a single full range planar virtually massless diaphragm. One quibble is the cushions with an integral foam sheet over the diaphragm area ...the foam disintegrates over time, and the cushions are stuck on with double sided tape which can get sticky. Another is the extreme hf is a little hot on my ancient pair, and this may have been dealt with in later versions or by more advanced energisers. But otherwise the very best open back design ever, regardless of silly priced "high end" alternatives. Driven from the right source they can go loud enough to give you permanent hearing loss. They also don't "sound" like closed back phones and therefore not the first choice of recording engineers in the same way they will mix on monopole monitors, but may have dipoles in the chill room for an expansive musical experience.. Why re-invent the wheel, Stax phones have remained virtually unchanged for 50 years because a full range electrostatic is exactly that with one caveat...their transparency to the source. Give them a quality source and they will produce for you a musical experience unmatched by virtually any other design.