Infinity RS-II: The Bookshelf Speaker That Defied Physics

Name: Infinity RS-II
Brand: Infinity

In the mid-1970s, when most bookshelf speakers struggled to produce anything below 80 Hz without distortion or boominess, Infinity introduced a compact speaker that seemed to break the laws of acoustics: the Infinity RS-II. Released in 1976, this unassuming two-way bookshelf speaker packed a sonic punch far beyond its size, thanks to a clever use of passive radiator technology and high-quality driver materials. Though not as widely remembered as some of Infinity’s larger floor-standing models, the RS-II holds a special place in vintage audio history as a pioneer in compact bass extension and a favorite among discerning listeners who valued accuracy and depth in a small package.

A Product of Innovation

Infinity (founded in 1968 by Arnie Nudell and Cary Christie) had already built a reputation for pushing the boundaries of speaker design by the time the RS-II arrived. Known for their servo-controlled subwoofers and time-aligned crossovers, the company brought serious engineering rigor to consumer audio. The RS-II, while modest in appearance, was no exception. It was designed as a compact monitor for near-field listening or as a secondary speaker in multi-room systems, but its performance belied its size.

The RS-II was part of Infinity’s “RS” (Reference Series) line, which aimed to deliver high fidelity at a more accessible price point than their flagship IRS models. Yet, it borrowed design philosophies from its more expensive siblings—particularly in its use of advanced materials and bass-loading techniques.

Technical Specifications

Specification	Detail
Type	2-way passive radiator bookshelf
Drivers	1" soft dome tweeter, 6.5" polypropylene woofer
Passive Radiator	One 6.5" passive radiator (rear-firing)
Frequency Response	45 Hz – 20 kHz (±3 dB)
Crossover Frequency	2.5 kHz
Sensitivity	87 dB (2.83V/1m)
Nominal Impedance	8 ohms
Recommended Amp Power	20–100 watts
Enclosure Type	Sealed with passive radiator
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 vinyl, rosewood vinyl

Sound Characteristics and Performance

The Infinity RS-II was engineered to deliver a remarkably balanced and extended sound for its era. Its most striking attribute was deep, tight bass—down to 45 Hz—unusual for a speaker under 15 inches tall. This was achieved through the use of a large, tuned passive radiator mounted on the rear panel, which allowed the sealed cabinet to produce bass frequencies without the port noise or chuffing common in bass-reflex designs.

The 6.5-inch polypropylene woofer provided a clean midbass response with low distortion, while the 1-inch soft dome tweeter offered smooth, non-fatiguing highs. Unlike some contemporary speakers that emphasized brightness to sound “detailed,” the RS-II leaned toward a more natural, neutral tonal balance. This made it particularly well-suited for acoustic music, jazz, and vocal recordings.

The crossover, though not as sophisticated as Infinity’s later time-aligned designs, was well executed for its class. Placed at 2.5 kHz, it kept the tweeter out of the upper midrange, reducing coloration and improving vocal clarity. Imaging was precise for a compact speaker, with a stable soundstage and good depth when properly positioned.

Many owners report that the RS-II benefits from being placed away from walls—despite its rear-firing radiator—due to the sensitivity of the passive radiator’s tuning to boundary interactions. With quality amplification (25–50 watts minimum), the RS-II could play loud and clean, handling complex passages with composure.

Notable Features and Innovations

The passive radiator design was the RS-II’s standout innovation. At a time when most small speakers used ported enclosures, Infinity’s choice of a passive radiator offered several advantages: no port turbulence, better transient response, and more consistent bass performance across volume levels. The radiator’s mass could be tuned precisely, allowing deeper bass extension from a smaller cabinet.

Another forward-thinking feature was the use of polypropylene for the woofer cone—a material that was still relatively new in consumer speakers in the 1970s. Polypropylene offered excellent damping, low resonance, and resistance to environmental changes, contributing to long-term reliability and consistent performance.

The cabinet, while not overly massive, was well-braced internally and finished with real wood veneers on higher-end units (though many were wrapped in high-quality vinyl). The overall build quality reflected Infinity’s commitment to engineering integrity over flashy aesthetics.

Common Issues and Maintenance

Like all vintage speakers, the Infinity RS-II can suffer from age-related wear. The most common issues include:

Tweeter degradation: The soft dome tweeters, while durable, can develop tears or lose damping fluid over decades, leading to harshness or distortion at high frequencies. Replacement with modern equivalents (such as Peerless or Vifa units) is possible with crossover adjustments.
Passive radiator fatigue: The rubber surround on the passive radiator can dry out and crack, causing flapping or reduced bass output. Re-foaming or surround replacement kits are available from specialty restoration shops.
Crossover component aging: Electrolytic capacitors in the crossover may dry out, altering frequency response. Replacing these with modern film capacitors can restore original performance and improve reliability.
Grille attachment: The original cloth grilles were held by plastic pegs that often break. Replacement grilles or magnetic retrofit kits are now available from vintage audio suppliers.

Regular inspection and gentle cleaning of the cabinet finish will help preserve the speaker’s appearance. For optimal performance, bi-wiring is not supported, but using high-quality speaker cable with solid connections is recommended.

Current Market Value and Collectibility

The Infinity RS-II is not as widely collected as some of Infinity’s more famous models (like the IRS V or the EMPIE), but it has a loyal following among vintage audio enthusiasts who appreciate its engineering and compact performance. In good condition, a pair typically sells for $250–$400 on the secondary market, with fully restored units commanding higher prices.

Factors that increase value include original grilles, unmodified crossovers, and rare wood finishes (such as real walnut). Speakers that have been professionally re-foamed and tested are more desirable than those needing restoration.

While not a “blue chip” collectible, the RS-II is increasingly recognized as an overlooked gem—a speaker that delivered high-end bass performance in a modest footprint, years before such feats became common with digital signal processing and powered designs.

Conclusion and Legacy

The Infinity RS-II may not have the star power of Infinity’s flagship systems, but it represents a quiet triumph of engineering ingenuity. By combining a passive radiator with quality drivers and a well-tuned crossover, Infinity created a compact speaker that could deliver deep, articulate bass and clear, natural mids and highs—something few competitors could match at the time.

Today, the RS-II stands as a testament to the idea that good sound doesn’t require big boxes. For vintage audio lovers seeking a compact speaker with real bass and honest tonality, the RS-II remains a compelling choice. It’s a speaker that rewards careful setup and quality amplification, offering a listening experience that feels surprisingly modern—even by today’s standards.

If you stumble upon a well-preserved pair, consider giving them a second life. With a little care, the Infinity RS-II can still hold its own in a world of digital audio and smart speakers—proving that true innovation never goes out of style.