Massdrop x Koss ESP/95X Electrostatic Systemsearch

Massdrop x Koss ESP/95X Electrostatic System

Massdrop x Koss ESP/95X Electrostatic System

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Discover the Electrostatic Difference

A revival of the standard-setting ESP/950 released by Koss in 1990, these headphones bring electrostatic quality into a whole new price bracket. Initially designed for live recording, the ESP/950 came with a large carrying case and a battery pack to power the required energizer: a special amplifier for electrostatic drivers. Made for the modern audiophile’s listening purposes, this version skips the case and battery pack to save on weight, space, and cost. The color has been updated to Massdrop’s exclusive midnight blue and the pleather ear pads swapped for thicker, more comfortable foam wrapped in velour. The rest stays true to the original: same clean bass and unmatched sound quality; same pivoting cups and adjustable, detachable headband; and same energizer, now with new graphics and colorway—all backed by the same lifetime warranty.

Note: This drop is limited to 200 units.  Shipping is free to US members and subsidized internationally.  At checkout, choose the 120V or 220V adapter.

Comparison to Moving-Coil Drivers

Invented in the 1800s and still widely used today, conventional moving-coil drivers feature a coil of wire inside a magnet glued to a stiff cone. Current passes through the coil and electromagnetism creates force that vibrates the coil, along with the stiff cone to which it’s glued. Electrostatic drivers operate based on a completely different, more advanced principle. They work by placing a static (non-moving) electric charge on an ultralight film floating between two perforated metal plates. Static cling and repulsion cause the entire film to move by itself when audio voltages are applied across the plates. Because there is no physical contact or interference from coils or stiff cones—and because the film is so thin—electrostatic headphones produce a superior sound, characterized by a lack of coloration and distortion. But since they require a high-voltage power supply and are more expensive, they have historically been less accessible than their moving-coil counterparts.

About Koss

If we were to write a history of audio companies in the US, Koss would land on the first page. Not only did the Milwaukee, Wisconsin–based company make the world’s first stereo headphone, the SP/3, in 1958, it’s also responsible for the first self-energizing electrostatic headphone, the first dynamic headphone to deliver all 10 audible octaves, and a standard-setting infrared wireless headphone. Over the years, Koss headphones have made it onto Air Force One, into the Smithsonian, and onto the heads of such music icons as Neil Diamond, Tony Bennett, and Pete Fountain. Founder John C. Koss was inducted into the Audio Hall of Fame in 1979 and the Consumer Electronics Hall of Fame in 2000. 



Reviews of the Original ESP/950


ESP/95X Electrostatic Headphones

  • Acoustic principal: Circumaural open-air design with minimal acoustic damping
  • Diaphragm: Ultra-low-mass 1.5-micron C-grade polyester film coated with semiconductive material
  • Diaphragm radiating surface area: 7 sq in (45.6 sq cm)
  • Frequency response: 8 Hz–35 kHz
  • Headband: Stainless steel, extendable
  • Headband cover: Wide leatherette-style vinyl with 12mm-thick polyethylene foam padding
  • Yokes: Horizontal and vertical pivoting with integral headband lock-and-detach mechanism
  • Cushions: Velour-wrapped foam
  • Cup size, including cushions (H x W x D): 5.9 x 3.9 x 1.6 in (15 x 10 x 4 cm)
  • Cable: Straight, dual entry, 4 ft (1.2 m) with 6 ft (1.8 m) extension 
  • Weight: 12.45 oz (353 g)

E/90X Electrostatic Energizer

  • Frequency response: 1.6 Hz–50 kHz (-3 dB), 100 Vrms differential output
  • THD + N: 0.001% at 1 kHz, 100 Vrms differential output
  • Input impedance: 100 kohms
  • Input level: 1 Vpk (for full power output)
  • Voltage amplification: 60 dB
  • Audio output voltage: 790 Vrms differential; 2,200 Vpk-pk differential with soft limiting
  • Channel separation: -80 dB at 1 kHz, 100 Vrms differential output
  • Signal-to-noise ratio: -100 dB at 100 Vrms output
  • Bias voltage supply: 600 VDC
  • Signal polarity: Absolute phase (non-inverting)
  • Volume control: Dual concentric continuous audio taper high-quality potentiometer with split shaft for balance
  • Switch: Power on/off rocker
  • Input jacks: RCA type (left and right), 3.5mm stereo, AC/DC adapter
  • Power: AC adapter power supply for E/90X (included, select 120V or 220V)
  • Power consumption: 320 mA DC current at normal listening levels
  • Dimensions (H x W x D): 2.6 x 4.3 x 6.1 in (6.5 x 11 x 15.5 cm)
  • Weight: 17 oz (482 g)


  • ESP/95X electrostatic headphones
  • E/90X electrostatic energizer
  • 120V or 220V AC adapter (add plug adapter for your country’s outlet)
  • 3 ft (0.9 m) RCA-to-RCA cable
  • 2 ft (0.6 m) 3.5mm–to-3.5mm cable
  • 6 ft (1.8 m) extension cable 
  • Koss's limited lifetime warranty (see warranty card)


All orders will be shipped by Massdrop.

Estimated ship date is Apr 15, 2019 PT.

After the drop ends, payment will be collected and the group’s order will be submitted to the vendor up front, making all sales final. Check the discussion page for updates on your order.