Infinity RS-9: The Forgotten Electrostatic Pioneer

Name: Infinity RS-9
Brand: Infinity

In the late 1970s, as high-end audio was undergoing a renaissance of innovation, Infinity Systems—already renowned for its groundbreaking EM speaker series and co-axial driver designs—ventured into uncharted territory with the RS-9, a full-range electrostatic hybrid loudspeaker. Though overshadowed by more famous contemporaries like the AR-3 or Quad ESL-57, and later eclipsed by the company’s own IRS series, the Infinity RS-9 stands as a bold, ambitious experiment in sonic transparency and engineering audacity. Rare, complex, and ahead of its time, the RS-9 represents a fascinating chapter in Infinity’s evolution and the broader story of electrostatic loudspeaker development.

Historical Context: Infinity at the Edge of Innovation

By the late 1970s, Infinity had established itself as a leader in driver technology, particularly with its Electro-Magnetic (EM) series, which used neodymium magnets and advanced dome tweeters to achieve exceptional clarity. But founder Arnold Nudell and design partner Cary Christie were never content with convention. Inspired by the purity of electrostatic speakers—favored by purists for their low distortion and point-source-like dispersion—they sought to overcome the inherent limitations of electrostatics: limited bass response, low sensitivity, and narrow dispersion.

The result was the RS-9, introduced in 1979 as a hybrid system combining a large electrostatic panel for midrange and treble with a powered bass section using conventional dynamic drivers. This approach foreshadowed the design philosophy of the legendary IRS (Infinity Reference Standard) series, which would debut a few years later and become one of the most iconic speaker systems in audiophile history.

Unlike the IRS, however, the RS-9 never achieved widespread commercial success. It was expensive, complex, and required careful setup and amplification. Only a small number were produced, making the RS-9 a true rarity today—one that flies under the radar even among seasoned vintage audio collectors.

Technical Specifications

Specification	Detail
Type	Electrostatic hybrid with powered bass
Frequency Response	35 Hz – 20 kHz (±3 dB)
Sensitivity	86 dB (2.83V/1m)
Impedance	Nominal 4Ω (varies with frequency)
Crossover	Active crossover at 500 Hz
High/Mid Driver	Large-area push-pull electrostatic panel
Bass Driver	Dual 10" long-throw woofers (ported)
Amplification	External 200W bass amp included
Inputs	Line-level and speaker-level inputs
Dimensions (H×W×D)	78" × 24" × 20" (per speaker)
Weight	~120 lbs (54 kg) per cabinet
Finish	Black textured vinyl or walnut veneer

The RS-9’s design is striking: a tall, narrow cabinet housing a vertical electrostatic panel flanked by bass ports and woofers at the base. The electrostatic section operates on a constant-charge principle, requiring a high-voltage bias supply (built into the cabinet) and careful insulation. The bass section is actively driven by a dedicated 200-watt amplifier module mounted within the speaker enclosure—a rarity for the era—and crossed over at 500 Hz via an external active crossover unit.

This hybrid topology allowed the RS-9 to deliver the speed, clarity, and imaging precision of electrostatics while avoiding the anemic bass response that plagued many pure electrostatic designs. The result was a speaker capable of both delicacy and authority—a true full-range system for its time.

Sound Characteristics and Performance

The sonic signature of the Infinity RS-9 is nothing short of captivating. When properly set up and driven by high-quality electronics, it delivers a transparent, low-distortion midrange that renders vocals and acoustic instruments with startling realism. The electrostatic panel’s near-massless diaphragm responds instantly to transients, resulting in a lively, articulate presentation with exceptional detail retrieval.

Imaging is precise and stable, with a wide, deep soundstage that seems to dissolve the speakers from the room. The vertical dispersion of the panel contributes to a natural, lifelike tonal balance, especially in the critical vocal range.

The powered bass section, while not as deep or tight as modern subwoofers, provides surprisingly robust low-end for a speaker of its era. The integration between the electrostatic panel and the dynamic woofers is generally seamless, though some listeners report a slight discontinuity in tonal character—common in early hybrid designs.

One caveat: the RS-9 demands high-current, high-damping-factor amplification for the electrostatic section, as its impedance dips sharply in the bass and midrange. Tube amps, while musically engaging, often struggle with control. Solid-state amplifiers with at least 100 watts per channel are recommended.

Notable Features and Innovations

The RS-9 was packed with forward-thinking engineering:

Integrated Bass Amplifier: One of the first consumer speakers to include an internal powered subwoofer section, predating modern active speakers by over a decade.
Push-Pull Electrostatic Design: Reduced distortion and increased output capability compared to single-ended electrostatics.
Active Crossover Network: Allowed precise control over driver integration and reduced intermodulation distortion.
Modular Construction: The crossover and power supply were designed for serviceability—a rarity in high-end audio of the time.

These features made the RS-9 not just a speaker, but a complete electroacoustic system, reflecting Infinity’s systems-oriented approach to loudspeaker design.

Common Issues and Maintenance

Owning an RS-9 today is a labor of love. These speakers are notoriously fragile and require careful maintenance:

Electrostatic Panel Degradation: Over time, the mylar diaphragm can develop tears or lose tension, leading to arcing or distortion. Humidity and dust accelerate this.
High-Voltage Power Supply Failure: The bias supply (typically 2–3 kV) can fail due to capacitor aging or arcing. Repairs require expertise in high-voltage electronics.
Bass Amplifier Reliability: The internal 200W amp uses older discrete components and is prone to overheating or transistor failure.
Crossover Capacitors: Electrolytic capacitors in the active crossover often need replacement after 40+ years.

Restoration is possible but costly. Specialists in vintage electrostatics—such as those who work on Sound Lab or Acoustat speakers—may be able to refurbish the panels. Replacement parts are scarce, but some DIY enthusiasts have reverse-engineered the crossover and power supply.

Current Market Value and Collectibility

The Infinity RS-9 is a sleeper collectible. While not as celebrated as the IRS V or the EM3, it holds significant historical value as a direct precursor to Infinity’s flagship line. In working condition, a pair can fetch $1,500–$3,000, depending on cosmetics and functionality. Non-working units sell for as little as $500, reflecting the high cost of restoration.

Collectors prize the RS-9 for its rarity, innovation, and connection to Arnold Nudell’s legacy. It’s a speaker that appeals to engineers and tinkerers as much as to audiophiles. For those seeking a true vintage high-end experience, the RS-9 offers a unique blend of electrostatic magic and dynamic punch.

Conclusion: A Hidden Gem of Electrostatic History

The Infinity RS-9 may not have achieved the fame of its successors, but it remains a remarkable achievement in loudspeaker design. It embodies the fearless experimentation that defined Infinity in the late 1970s—a time when the boundaries of high-fidelity were being redrawn.

For the vintage audio enthusiast, the RS-9 is more than just a speaker: it’s a piece of engineering history, a bridge between the purity of electrostatics and the practicality of dynamic bass. It’s not for the faint of heart—nor the unskilled hand—but for those willing to restore and cherish it, the RS-9 offers a listening experience that is ethereal, engaging, and utterly unforgettable.

If you stumble upon a pair in good condition, consider it not just a purchase, but a rescue mission—and a chance to own one of the rarest, most innovative hybrids of the golden age of hi-fi.