What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

ESS amt-1a

A loudspeakers translates electrical impulses into sound waves: Ideally,the loudspeakers/translator leaves nothing out and puts nothing extraneous in. It doesen't omit or color or mask. The perfect translator is perfectly simple. Simple and impossible until the Heil AirMotion Transformer revolutionized sound reproduction. The Heil midrange/high-frequency transformer is the perfect translator. There is only one compact system with a full-size Heil. The ESS amt-1a Bookshelf system. perfectly simple.

Your ears will appreciate the difference

Air-Motion Transformation: Midrange/High-Frequency

The Heil transformer, like most significant innovations, is much appreciated but a little mysterious. It is mandatory equipment for master reproduction techniques, yet the technological basis for its performance is often taken for granted. Actually, the Heil Principle of Air-Motion Transformation is as elegantly simple as it is effective.

The transformer's diaphragm resembles a lightweight pleated curtain mounted between powerful ceramic bar magnets. Conductive strips on the sides of each pleat cause the pleats to expand or contract in step with the signal. The air is squeezed out, and accelerated to five times the velocity of the diaphragm itself. In effect the Heil transformer uses air to move air, operating on the principle of pneumatic leverage.

Cone driving systems, on yhe other hand, are sluggish and inefficient by design. The cone's mass is huge, driving energy is largely devoted to overcoming its great inertia. The cone resonates and can "break up" at high frequencies. Acone driver only pushes air like a piston, in a one-to-one ratio.

The Heil driver's air-motion transformation ratio is five times better than that of any conventional speaker.

Other crucial design parameters are solved by the Heil Air-motion Transformer. The extremely light weight of its diaphragm eliminates resonance. Since the driving impulse is spread uniformly over the diaphragm surface, harmonic distortion from "cone breakup" is non-existent. These are inherent benefits of the Heilo design. For conventional speakers, they remain problematic goals.

REmarkable dispersion characteristics are another natural advantage of the amt's desugn. With a 120° pattern at 16 kHz, the amt maintains a solid expanse of stereo imagery to frequencies beyond audibility. Whatever the speaker/listener positioning, imaging is precise and penetrating.

The audible payoff is clarity, a perfect re-creation of the music 's fine and changing texture. Female vocal depth, the harmonic complexities of bow against string, and fleeting nuances of program ambience emerge with presence, immediacy, and power. It's all there.

Low Frequency performance

Deep, articulate low frequency response is provided by teh same 12" bass driver used in the top system of the ESS line, the amt-1a. Its 7 lb. 6,5 oz (3,36 kg) magnet assembly, rigid die-cast frame, and large-radius coil ensure state-of-the-art bass performance and dependability - response that feels substantial in the lower registers.


The amt-1a Bookshelf system is designed to convert high power loads into clean; full sound, without effort and without distortion. The air-motion transformer's Teflon diaphragm both resists and dissipates heat outstandingly. The bass driver's 2" coil and high-temperature cone composition are significant factors in the system's low-end strength. "At power" the amt-1a Bookshelf is clear and dependable after other compact systems have reached their limits.

Dividing Network

The sophisticated crossover network designed for the amt-1a Bookshelf operates at 850 Hz, providing excellent woofer/amt phasing and precise signal distribution. Air-cored inductors are used to avoid the high-amplitude distortion possible with metal cored units. Altough air-cored inductors are an unseen refinement, they significantly enhance the linearity of a dividing network.


Your listening environment's acoustic character may prompt some fine adjustment of teh speaker system. A continuosly variable attenuation or accentuation control affects 850 Hz to beyond hearing, without blunting or peaking the higher frequencies and upper harmonics. The control panel is situated at the rear of the cabinet for easy access.

The construction of the amt-1a Bookshelf speaker enclosure reflects the same concern for distortion-free reproduction shown in the system's hardware. The interior dimensions of the enclosure are meticulously coordinated to the bass driver's specific characteristics. precise mathematical tuning determines port design.

Walnut veneer is matched, fitted to the cabinet superstructure, and hand-finished from sanding to final rubdown. A strong weave of sonically-transparent polyester fiber is used in the grille treatment, completing the speaker's appearance of simple, Functional grace.

The Final Arbiter

A classic integrity, from cabinetry to driver mounting detail, pervades the manufacture of the amt-1a Bookshelf. Its superiority can be demonstrated in many ways, reflected at lenght in technical data. But to the final arbiter, your ear, There is only proof. The audible proof. A critical evaluation of the amt-1a Bookshelf speaker system will reveal how perfect translation can be.


Power Capacity: 75 watts continuous ; 350 watt peak Circuit breaker protected

Nominal Impedance: 4 ohms

Dispersion: 120 ° horizontal, 30° vertical

Crossover frequency: 850 Hz

Efficiency: 1 watt input produces 82 dB sound pressure at a distance of 15 feet (4 m)

Frequency Response: 50 - 20,000 Hz, ±3 dB

Heil Air-Motion Transformer

Total Radiating Area: 29 sq. in. (187,24 cm²)

Transformation Ratio: 5.0:1 velocity increase

Magnet Assembly Weight: 12 lbs. 15 oz. (5,87 kg)

Flux Density: 4,500 Gauss

Square Wave Rise Time: 15 microseconds at 5,000 Hz

Low Frequency Driver

Nominal Diameter: 12" (30,48 cm)

Voice Coil: 2" (5,08 cm)

Magnetic Assembly Weight: 7 lbs. 6,5 oz. (3,36 kg)

Flux Density: 10,500 Gauss


Midrange/High Frequency: Continuously variable attenuation oraccentuation from 1 kHz to beyond audibility


Finish: Oiled walnut veneer

Grille Color: Brown

Dimensions: 24" x 14" x 14" (60,96 x 35,56 x 35,56 cm)

Shopping Weight: 60 lbs (27,27 kg)

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