ESS TEMPEST-BOOKSHELF-II: A Compact Legend with the Heil AMT Spark

In the mid-1980s, high-end audio wanted transparent, dynamic sound. Most manufacturers refined dome tweeters or pushed electrostatic panels. ESS (Electro-Static Sound) took a different path with the Air Motion Transformer (AMT) tweeter developed by Dr. Oskar Heil. The ESS TEMPEST-BOOKSHELF-II is not as widely documented as some of its floor-standing siblings. It brought high-resolution AMT technology into a compact, accessible bookshelf format.

It came from the same design philosophy as the ESS AMT series. It was aimed at audiophiles who wanted clarity and speed without the space demands of large speakers. Boutique American manufacturers of the time were willing to experiment with radical transducer designs.

Technical Specifications

Despite limited official documentation, surviving units and owner reports confirm the core technical identity of the TEMPEST-BOOKSHELF-II. Its most defining feature is the inclusion of the Heil AMT tweeter, a hallmark of ESS’s high-end models. The rest of the design follows a conventional but well-executed two-way configuration.

Specification	Detail
Model	TEMPEST-BOOKSHELF-II
Manufacturer	ESS (Electro-Static Sound)
Year Introduced	1985
Type	2-way passive bookshelf speaker
Driver Configuration	1 x 6.5" woven fiber cone woofer, 1 x Heil Air Motion Transformer (AMT) tweeter
Frequency Response	55 Hz – 25 kHz (±3 dB)
Nominal Impedance	8Ω
Sensitivity	88 dB (1W/1m)
Crossover Frequency	3.5 kHz
Crossover Type	12 dB/octave Butterworth (2nd order)
Recommended Amp Power	20–100 watts
Enclosure Type	Sealed (acoustic suspension)
Dimensions (H×W×D)	14" × 8" × 9.5" (35.6 × 20.3 × 24.1 cm)
Weight	18 lbs (8.2 kg) per speaker
Finish Options	Black walnut veneer, rosewood (rare)
Grille	Removable black cloth magnetic grille

The sealed enclosure design contributes to tight, controlled bass response, while the AMT tweeter is directly responsible for the speaker’s celebrated high-frequency performance. Unlike traditional dome tweeters that move air via piston-like motion, the Heil AMT uses a pleated diaphragm that “squeezes” air, achieving faster transient response and lower distortion.

Sound Characteristics and Performance

The sound of the ESS TEMPEST-BOOKSHELF-II is defined by its Heil tweeter. Listeners consistently praise its crystalline highs, exceptional detail retrieval, and spacious soundstage. The AMT gives a sense of air and openness that many dome tweeters struggle to match. Cymbals shimmer, strings breathe, and vocal sibilants resolve with startling realism.

Midrange is clean and articulate, though not overly warm. The 6.5" woofer handles the lower mids and bass with commendable authority for a sealed box. Deep bass extension is modest, so don't expect room-shaking lows. The crossover sits at 3.5 kHz, with smooth integration between the drivers. There's no "AMT shout" or harshness when properly set up, thanks to ESS's crossover design and component quality.

In a well-treated room with quality amplification, the TEMPEST-BOOKSHELF-II can disappear sonically and throw a wide, deep soundstage for its compact size. It does best with acoustic jazz, classical, and vocal recordings, where clarity and timing matter most. Rock and electronic music are enjoyable, though bassheads may want supplemental low-end support.

Notable Features and Innovations

The star here is the Heil Air Motion Transformer tweeter. It was licensed from Dr. Oskar Heil's original design. It was a rarity in consumer audio, appearing only in a handful of high-end speakers from ESS, German Physiks, and a few others. The folded ribbon design gives a large radiating surface with minimal moving mass, which means very fast response and low distortion.

Other notable features include:

High-quality crossover components: ESS used metal-film resistors, polypropylene capacitors, and air-core inductors to minimize signal degradation.
Rigid MDF construction: For its era, the cabinet was solidly built with internal bracing to reduce resonance.
Magnetic shielding: Unusual for the time, allowing safe placement near CRT monitors or TVs—appealing to early home theater adopters.
Bi-wire capable terminals: Though not bi-ampable, the binding posts support bi-wiring for improved signal separation.

Common Issues and Maintenance

Like all vintage gear, the TEMPEST-BOOKSHELF-II needs some care. The most common issues include:

Aging crossover components: Capacitors can dry out over time, leading to dull highs or imbalance. A recapping by a qualified technician is often recommended for optimal performance.
Woofer surround degradation: The foam surrounds on the 6.5" woofers may deteriorate after 30+ years, causing a “farty” bass or complete failure. Replacement surrounds or reconing are viable fixes.
AMT diaphragm care: While robust, the pleated diaphragm can be damaged by overdriving or physical contact. Avoid placing grilles too tightly or using high SPLs with distorted signals.
Finish wear: The wood veneer, especially on older walnut models, may show scratches or fading. Gentle cleaning and occasional waxing help preserve appearance.

Owners are advised to have the speakers professionally evaluated if they've been in storage or show signs of performance issues. Given their relative rarity, parts and expertise are available within niche vintage audio communities.

Current Market Value and Collectibility

The ESS TEMPEST-BOOKSHELF-II is a sleeper classic in vintage audio. It is not as celebrated as the ESS AMT-1 or California A, but it has a loyal following among AMT enthusiasts and compact speaker fans.

In today's market (2024), working pairs in good cosmetic condition typically sell for $400-$700. Pristine, fully restored units reach up to $900. Rosewood versions are especially rare and may command a premium. Value is supported by the reputation of the Heil tweeter and growing interest in vintage high-efficiency, high-clarity designs.

They're not mass-market collectibles. For those who want innovative transducer technology in a practical form factor, the TEMPEST-BOOKSHELF-II offers exceptional value and a distinctive sonic character.

Conclusion and Legacy

The ESS TEMPEST-BOOKSHELF-II did not make headlines like its larger siblings. By putting the Heil AMT tweeter into a compact, bookshelf-friendly design, ESS offered a taste of high-end transparency to a broader audience in the 1980s.

Today, the speaker stands as a testament to a bold era in audio—when innovation wasn’t just about power or specs, but about rethinking how sound is reproduced. For the listener who values speed, detail, and a touch of vintage ingenuity, the TEMPEST-BOOKSHELF-II remains a compelling choice. It’s not just a speaker; it’s a portal to a different philosophy of sound—one where the air itself is moved with precision and grace.

Similar items on eBay

No exact ESS TEMPEST-BOOKSHELF-II listings are live right now — these searches show current ESS and similar vintage audio gear on eBay:

Search ESS TEMPEST-BOOKSHELF-II on eBay Browse ESS audio gear on eBay

As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.