ES Lab ES-HE90 Open-Back Electrostatic Headphone

Some headphones are remembered for decades after they leave the catalog. The Sennheiser HE90 Orpheus is one of them: a glass-electrode electrostatic flagship from the early 1990s that now changes hands, when it does at all, for collector money. The ES Lab ES-HE90 is the Hong Kong workshop's answer to that legacy. It is the product of several years of development by a team that spent years repairing and studying original HE90s, built to recreate the sonic essence of that classic with modern precision, in a bubinga wood housing that looks as good on the stand as it sounds on the head.

Type and Technology

The ES-HE90 is an open-back electrostatic headphone. Its driver electrodes are made from high-strength glass, chosen for dimensional stability and minimal warping. Around five thousand hexagonal holes are formed in each electrode by high-precision laser cutting combined with chemical etching, at micron-level accuracy and without micro-cracks that would compromise the substrate. A sputtered chromium layer and a pure gold coating provide high conductivity and long-term oxidation resistance.

The diaphragm is an ultra-thin engineering plastic only 1 micron thick, with an elliptical shape rather than the traditional circular design to reduce standing waves. Driver assembly is carried out entirely in a cleanroom, where a technician inspects every one of the holes on each of the four electrodes to eliminate particle contamination.

The ES-HE90 uses a 5-pin STAX Pro bias connector, so it requires a compatible electrostatic energizer or amplifier and cannot be driven from a conventional headphone output.

Sound Character

Early impressions from the Shenzhen International Audio Show describe a bright, transparent, and ethereal presentation, with the effortless openness and airy treble shimmer that made the original HE90 an icon. Detail retrieval is a strength, and the overall signature leans light on the body of instruments and vocals.

The ear pads are the tuning control. Different ear pad combinations let the owner choose between a voicing that closely recreates the original classic sound signature and one optimized for modern recordings.

Build and Comfort

The housing is crafted from African bubinga wood, selected after extensive testing of different woods for the most complementary resonant characteristics. It goes through multiple stages of sanding, finishing, coating, and polishing. The ear pads use selected imported polyurethane foam, balanced for density, hardness, and breathability, and are hand-assembled in the ES Lab workshop. The headband is finished in black leather.

At 370 grams without the cable, the ES-HE90 is light for a headphone of this scale, and the clamp force is gentle, so it settles on the head and stays comfortable through long sessions. The design is fully modular: ear pads, headband, and cable can be assembled or replaced by hand.

Best For

Listeners who want the open, airy electrostatic experience of a legendary flagship without a five-figure collector's price. It suits critical listening of acoustic, vocal, and orchestral recordings in a quiet room, and it pairs with any quality STAX Pro bias electrostatic energizer or amplifier.

What's in the Box

• ES Lab ES-HE90 open-back electrostatic headphone
• 2.3 m cable with 5-pin STAX Pro bias connector
• Wooden storage and transport case

Specifications