Infinity BETA-ES250: The Electrostatic Elegance of a Forgotten Hybrid

In the mid-1980s, high-end audio was going through a burst of new ideas, and Infinity Systems, already known for its speaker designs, introduced the BETA-ES250. It was not a conventional dynamic loudspeaker or a full-range electrostatic. It was a hybrid electrostatic design that paired an electrostatic midrange and treble panel with a dynamic bass driver. It sat at the premium end of Infinity's BETA series. The idea was to get the speed and transparency of electrostatic panels along with the low-end extension and room-filling power of conventional cone drivers.

It is not as widely recognized as the IRSV or the mass-market Beta series bookshelf models, but it has its own niche in vintage audio history. It reflects a bold engineering approach from a time when manufacturers were pushing hard on what home audio reproduction could do.

Technical Specifications

The BETA-ES250’s design centers around a large, vertically oriented electrostatic panel that handles frequencies above 500 Hz. This panel, constructed with a thin, electrically charged diaphragm suspended between perforated stator plates, delivers the near-instantaneous transient response and low distortion characteristic of electrostatic transducers. Below 500 Hz, a dedicated 12-inch dynamic woofer takes over, housed in a transmission-line cabinet that enhances bass extension and reduces resonance.

The crossover between the electrostatic panel and the woofer is carefully engineered to ensure a smooth transition, avoiding the “crossover dip” or phase anomalies that often plague hybrid designs. The result is a speaker that aims for both accuracy and emotional engagement.

Sound Characteristics and Performance

The electrostatic panel gives the Infinity BETA-ES250 a level of clarity and airiness in the midrange and treble that few dynamic drivers can match. Vocals come through with startling realism, including individual breaths, subtle inflections, and harmonic textures. Violins, acoustic guitars, and cymbals have lifelike presence and spatial precision.

The 12-inch woofer is not as fast as the electrostatic panel, but it is well integrated and gives deep, articulate bass down to 35 Hz. The transmission-line design keeps the bass taut and controlled, without the boominess that sometimes plagues ported enclosures. The overall balance is neutral to slightly warm, so the ES250 suits classical recordings, jazz trios, and rock.

The soundstage is one of the most praised things about the BETA-ES250. The electrostatic panel produces a wide, three-dimensional image with excellent depth and instrument separation. Listeners often report that the speakers have "disappeared," leaving only the music suspended in space.

Like all electrostatic designs, the ES250 has a directional dispersion pattern. The sweet spot is relatively narrow, so placement and listener position need care. Sensitivity is respectable at 89 dB, but the electrostatic panel wants clean, stable amplification, especially in the upper frequencies where voltage swings can be high.

Notable Features and Innovations

The BETA-ES250 was more than another speaker in Infinity's lineup. It showed real technological ambition. Its most notable features:

• Hybrid Electrostatic Design: At a time when full electrostatic speakers (like the Quad ESL-57 or KLH Model Nine) were admired but limited by bass performance, Infinity’s hybrid approach offered a practical compromise. The ES250 delivered electrostatic clarity without sacrificing low-end authority.

• Transmission-Line Bass Cabinet: The woofer is housed in a long, folded transmission line that acts as an acoustic labyrinth, absorbing rear-wave energy and reinforcing bass output. This design reduces distortion and enhances low-frequency extension.

• Modular Construction: The electrostatic panel and woofer section are built as separate modules within the same cabinet, allowing for easier servicing and alignment.

• High-Voltage Power Supply: Each speaker contains an internal power supply that generates the high voltage (typically 2–3 kV) required to charge the electrostatic diaphragm. This eliminates the need for external power units, a convenience compared to some electrostatic competitors.

• Aesthetic Elegance: With its tall, narrow profile and fine wood veneer finishes, the ES250 was as much a piece of furniture as it was audio equipment. The perforated metal stator grille adds a futuristic touch, hinting at the advanced technology within.

Common Issues and Maintenance

As with any vintage electrostatic speaker, the BETA-ES250 needs attentive care. Over time, several issues may come up:

• Diaphragm Degradation: The ultra-thin Mylar diaphragm in the electrostatic panel can become brittle or develop static cling, leading to distortion or “crackling” sounds. Re-lacing or re-paneling by a specialist may be necessary.

• Stator Corrosion: If exposed to high humidity, the metal stators can corrode, causing arcing or reduced output. Keeping the speakers in a dry environment is essential.

• Power Supply Failure: The internal high-voltage supply uses aging capacitors and transformers that may fail after decades. A recapping by a qualified technician is often recommended for long-term reliability.

• Woofer Surround Deterioration: The foam or rubber surrounds on the 12-inch woofer may dry out and disintegrate. Replacement surrounds or full reconing are common restoration steps.

Owners are advised to keep the speakers away from walls, since humidity buildup can raise the risk of arcing. Regular dusting with a soft brush or anti-static cloth helps maintain performance.

Current Market Value and Collectibility

The Infinity BETA-ES250 is a rare find today. It never matched the commercial success of Infinity's more mainstream Beta speakers, and production numbers were relatively low. Working pairs in good condition can command $800 and $1,500, depending on cosmetic condition, functionality, and whether they've been restored.

Collectors of vintage hybrid speakers, particularly those interested in how electrostatic technology developed, value the ES250 for its engineering and its sound. It is not as well known as the Quad ESLs or the Acoustat models, but it is an interesting chapter in American speaker design.

Its hybrid nature also makes it more practical than full electrostatics for modern use, especially in larger rooms or with dynamic music genres.

Conclusion and Legacy

The BETA-ES250 comes from an era when manufacturers were willing to try radical technologies in pursuit of sonic perfection. Infinity blended electrostatic clarity with dynamic bass and aimed for both refinement and realism.

It is overshadowed by more famous models, but the BETA-ES250 is a sophisticated, forward-thinking design. It offers the speed and transparency of electrostatics, grounded by the warmth and power of a well-engineered woofer.

The BETA-ES250 sits between two approaches to speaker design, electrostatic and dynamic. For those willing to restore it, it remains a choice for high-fidelity listening with a touch of vintage elegance.

Similar items on eBay

No exact Infinity BETA-ES250 listings are live right now — these searches show current Infinity and similar vintage audio gear on eBay:

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

Related Models

• Infinity 2000.3
• Infinity 2000-II (1975)
• Infinity 2500
• Infinity EMIT-R
• Infinity ES-200 (1978)
• Braun AUDIO-1 (1965)
• Braun AUDIO-250 (1965)
• Magnavox Component Systems (1972)
• Acoustic Research AR (1967-1976)
• Acoustic Research 11