ESS TEMPEST-SERIES: The Forgotten Flagship of Planar Innovation

ESS (Electro-Static Sound) was one of the names audiophiles talked about in the 1980s. The company was best known for its planar magnetic loudspeakers. The TEMPEST-SERIES was one of its most ambitious and elusive products, a rare, limited-production line of hybrid planar speakers from the company's peak years.

The TEMPEST-SERIES is not as well documented as ESS's more famous models like the CA-1 or Model Eight, but it has a cult following among vintage audio collectors. The idea was to merge the speed and transparency of planar magnetics with the dynamic authority of conventional cone drivers. The speaker was hard to drive and rare to find. Many who heard it still describe it as "revelatory."

Historical Context: ESS in the 1980s

ESS was founded in the late 1970s by a group of audio engineers with backgrounds in aerospace and acoustics. It adopted planar magnetic technology at a time when electrostatics and dynamic drivers dominated the high-end market. The breakthrough was the Model Four, a full-range quasi-ribbon driver with extraordinary transient response and low distortion.

By the mid-1980s, ESS was working on larger, more ambitious designs, and the TEMPEST-SERIES was the result. It was introduced around 1985 and marketed as a "reference-grade" system for serious audiophiles and professional studios. It was never mass-produced. Surviving units are exceptionally rare today, and they tend to get passed quietly among collectors or restored by dedicated enthusiasts.

Technical Specifications

The TEMPEST-SERIES was a floor-standing hybrid planar loudspeaker, combining ESS’s signature quasi-ribbon drivers with conventional woofers to overcome the bass limitations inherent in planar designs. Each speaker featured a vertical array of drivers, housed in a tall, narrow cabinet with a sleek, minimalist aesthetic typical of high-end gear from the era.

Specification	Detail
Type	3-way hybrid floorstanding loudspeaker
Driver Configuration	Dual ESS quasi-ribbon planar mid/high drivers, dual 10" woven-fiber woofers
Frequency Response	35 Hz – 22 kHz (±2 dB)
Sensitivity	86 dB (2.83V/1m)
Nominal Impedance	4 ohms (minimum 3.2 ohms)
Crossover Frequencies	350 Hz (woofer to mid), 2.5 kHz (mid to high)
Crossover Type	2nd-order passive, air-core inductors, polypropylene capacitors
Enclosure Design	Transmission-line loaded bass section with damped internal chambers
Dimensions (H×W×D)	48" × 14" × 20" (122 cm × 35.5 cm × 51 cm)
Weight	85 lbs (38.5 kg) per speaker
Recommended Amplifier	50–200 watts, high-current capable

Notably, the quasi-ribbon drivers used in the TEMPEST-SERIES were made with ultra-thin conductive filaments suspended in a magnetic field—similar in principle to Magnepan or Apogee designs, but with ESS’s proprietary tensioning and damping techniques. This allowed for faster transient response and lower intermodulation distortion compared to traditional dome tweeters.

The bass section utilized dual 10-inch woofers in a transmission-line configuration, which extended low-frequency response while minimizing port noise and group delay. This hybrid approach was key to the TEMPEST’s ability to deliver both the delicacy of planar mids and the physical impact of deep bass.

Sound Characteristics and Performance

Listeners used to conventional dynamic speakers found the sound of the TEMPEST-SERIES transformative. Its most celebrated attribute was imaging precision. Instruments were rendered with laser-like focus, and the soundstage was expansive, deep, and layered with exceptional spatial resolution.

Midrange clarity stood out. Vocals were reproduced with uncanny realism, with breaths, sibilance, and emotional nuance all present in a way few speakers of the era could match. The planar drivers have no cone breakup and very little moving mass. That gives an almost "disappearing" quality, where the speakers seem to vanish acoustically.

High frequencies were smooth and extended, without the harshness sometimes associated with early ribbon or metal-dome tweeters. The TEMPEST was not a "bright" speaker. It leaned toward neutrality with a slight warmth in the upper mids, likely due to the crossover integration and cabinet damping.

Bass was solid for a hybrid planar, though it demanded a well-matched amplifier and careful room placement. The transmission-line woofers gave a tight, articulate low end but lacked the sheer slam of large sealed or ported dynamic designs. When properly set up, the integration between the planar and cone drivers was very good.

Notable Features and Innovations

Dual Quasi-Ribbon Arrays: The use of two vertically stacked planar drivers allowed for increased radiating surface and improved power handling, reducing distortion at higher volumes.
Transmission-Line Bass: Uncommon in planar hybrids, this design choice enhanced bass control and reduced resonance.
Point-Source Mid/High Array: The close vertical alignment of the planar drivers created a coherent wavefront, improving off-axis response and imaging stability.
Hand-Wound Crossovers: Each unit featured individually assembled crossovers with premium components, reflecting ESS’s commitment to quality.

Common Issues and Maintenance

Owning a pair of TEMPEST-SERIES speakers today takes work. Because of their age and limited production, several issues commonly come up:

Diaphragm Sag: The thin conductive filaments in the planar drivers can degrade or sag over decades, leading to distortion or buzzing. Restoration often requires re-tensioning or replacement.
Crossover Component Aging: Capacitors and inductors may drift in value or fail. Rebuilding the crossover with modern equivalents is often necessary.
Woofers Wear: The 10" bass drivers, while robust, may suffer from surround deterioration. Re-foaming or reconing is typically required.
Low Sensitivity and 4-Ohm Load: These speakers demand powerful, current-rich amplifiers. Tube amps or low-damping-factor solid-state units may struggle to control the bass.

Restoration specialists familiar with vintage planar speakers are rare, but communities like The Audio Circle and Audiokarma have documented successful rebuilds. Original parts are hard to find, so many restorers use compatible drivers from Magnepan or custom-built replacements.

Current Market Value and Collectibility

Genuine ESS TEMPEST-SERIES speakers are extremely rare. Fewer than 200 pairs are believed to have been made, and most remain in private collections. When one does appear on the market, typically via eBay, Audiogon, or specialty forums, it often sells quickly to collectors.

As of 2024, unrestored pairs trade between $1,200 and $2,000. Fully restored units with upgraded crossovers and drivers can command $3,500 or more. Their value is driven more by historical significance and engineering interest than by widespread fame, which makes them a "sleeper" in the vintage audio market.

They are particularly prized by enthusiasts of planar magnetic technology and by those seeking an alternative to the more common Magnepan or Apogee speakers of the era.

Conclusion: A Legacy of Innovation

The ESS TEMPEST-SERIES never achieved the commercial success of its contemporaries. Its influence can be seen in modern hybrid designs from companies like MartinLogan and Revel.

For the vintage audio enthusiast, the TEMPEST-SERIES is more than just a speaker—it’s a piece of audio archaeology, a testament to a time when innovation was driven by passion, not profit. Finding, restoring, and hearing a pair in full cry is a rare privilege—one that connects the listener not just to music, but to the very spirit of analog excellence.

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