Infinity RS-9: The Forgotten Electrostatic Pioneer

In the late 1970s, Infinity Systems already had its EM speaker series and co-axial driver designs behind it. Then it built the RS-9, a full-range electrostatic hybrid loudspeaker. The AR-3 and Quad ESL-57 are better known, and the company's own IRS series later eclipsed it. The Infinity RS-9 was still a bold, ambitious experiment in transparency. It is rare and complex, and it came before its time.

Historical Context: Infinity at the Edge of Innovation

By the late 1970s, Infinity was a leader in driver technology, particularly with its Electro-Magnetic (EM) series. Those used neodymium magnets and advanced dome tweeters to get exceptional clarity. Founder Arnold Nudell and design partner Cary Christie were never content with convention. Purists favor electrostatic speakers for their low distortion and point-source-like dispersion. Nudell and Christie wanted that, and they wanted to overcome the limits of electrostatics: limited bass response, low sensitivity, and narrow dispersion.

The answer was the RS-9, introduced in 1979 as a hybrid system. A large electrostatic panel handles midrange and treble, and a powered bass section uses conventional dynamic drivers. This approach foreshadowed the design of the IRS (Infinity Reference Standard) series, which debuted a few years later and became one of the most famous speaker systems in audiophile history.

Unlike the IRS, the RS-9 never sold widely. It was expensive and complex, and it needed careful setup and amplification. Only a small number were produced, so it is a real rarity today. It 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

When properly set up and driven by high-quality electronics, the Infinity RS-9 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. The result is 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 is not as deep or tight as a modern subwoofer, but it gives surprisingly strong low end for a speaker of its era. The electrostatic panel and the dynamic woofers generally blend well. Some listeners report a slight discontinuity in tonal character, which is common in early hybrid designs.

One caveat: the RS-9 demands high-current, high-damping-factor amplification for the electrostatic section, because its impedance dips sharply in the bass and midrange. Tube amps are musically engaging but 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.

All of this makes the RS-9 a complete electroacoustic system and not just a speaker. It reflects Infinity's systems-oriented approach to loudspeaker design.

Common Issues and Maintenance

Owning an RS-9 today takes work. 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. It is not as celebrated as the IRS V or the EM3, but it is 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, which reflects the high cost of restoration.

Collectors prize the RS-9 for its rarity, innovation, and connection to Arnold Nudell's legacy. It appeals to engineers and tinkerers as much as to audiophiles.

Conclusion: A Hidden Gem of Electrostatic History

The Infinity RS-9 did not reach the fame of its successors, but it is a remarkable achievement in loudspeaker design. It reflects the experimentation that defined Infinity in the late 1970s.

The RS-9 is a piece of engineering history, a bridge between the purity of electrostatics and the practicality of dynamic bass. It is not for the faint of heart or the unskilled hand.

A pair in good condition is a chance to own one of the rarest hybrids of the golden age of hi-fi.

Market Value

┌──────────────────────────────────────────────────────────────────────────┐
│ INFINITY RS-9                                                   Aug 2026 │
├──────────────────────────────────────────────────────────────────────────┤
│ High      $255                                    Latest             $69 │
│ Median    $69                                     Trend           ▼ Down │
│ Low       $45                                     Volume           ~1/mo │
├──────────────────────────────────────────────────────────────────────────┤
│   $300 ┤                                                                 │
│        │                                                                 │
│        │.                                                                │
│   $171 ┤                                                                 │
│        │                                                                 │
│        │                                                                 │
│        │                  .                                             .│
│     $0 ┤                                                                 │
│        ├─────────────────────────────────────────────────────────────────│
│    vol │█                 █                                             █│
│        └─────────────────────────────────────────────────────────────────│
│         2026-02                      2026-05                      2026-07│
└──────────────────────────────────────────────────────────────────────────┘

eBay completed sales. Excludes accessories, parts, and non-working units. Hover points for details.