Infinity RS-II: The Bookshelf Speaker That Defied Physics

In the mid-1970s, most bookshelf speakers struggled to produce anything below 80 Hz without distortion or boominess. Infinity's answer was the Infinity RS-II, released in 1976. It was a small two-way bookshelf speaker that hit well above its size, thanks to a passive radiator and good driver materials. It isn't as widely remembered as Infinity's larger floor-standing models. It was a pioneer in compact bass extension, and listeners who valued accuracy and depth in a small package favored it.

A Product of Innovation

Infinity was founded in 1968 by Arnie Nudell and Cary Christie. By the time the RS-II arrived, the company already had a reputation for pushing speaker design, with servo-controlled subwoofers and time-aligned crossovers. The RS-II was modest to look at, but it got the same engineering rigor. It was designed as a compact monitor for near-field listening or as a secondary speaker in multi-room systems. 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 than the flagship IRS models. It borrowed design ideas from its more expensive siblings, particularly the advanced materials and the 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 delivered a balanced, extended sound for its era. Its most striking attribute was deep, tight bass - down to 45 Hz - which was unusual for a speaker under 15 inches tall. The key was a large, tuned passive radiator on the rear panel. It let the sealed cabinet produce bass without the port noise or chuffing common in bass-reflex designs.

The 6.5-inch polypropylene woofer gave clean midbass with low distortion. The 1-inch soft dome tweeter gave smooth, non-fatiguing highs. Some contemporary speakers emphasized brightness to sound "detailed." The RS-II leaned toward a natural, neutral tonal balance instead, which suited acoustic music, jazz, and vocal recordings.

The crossover isn't as sophisticated as Infinity's later time-aligned designs, but it was well executed for its class. It sits at 2.5 kHz, which keeps 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 does better away from walls, even though the radiator fires from the rear. The reason given is that the passive radiator's tuning is sensitive to boundary interactions. With quality amplification (25-50 watts minimum), the RS-II could play loud and clean and handle complex passages with composure.

Notable Features and Innovations

The passive radiator design was the RS-II's standout innovation. Most small speakers then used ported enclosures. Infinity's passive radiator offered several advantages: no port turbulence, better transient response, and more consistent bass across volume levels. The radiator's mass could be tuned precisely, which allowed deeper bass from a smaller cabinet.

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

The cabinet wasn't overly massive, but it was well braced internally. Higher-end units had real wood veneers, though many were wrapped in high-quality vinyl. Build quality put engineering ahead of flashy looks.

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 may dry out and crack over time, potentially 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 its appearance. Bi-wiring is not supported. 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). 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, and fully restored units command higher prices.

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

It isn't a "blue chip" collectible, but the RS-II is increasingly recognized as an overlooked gem. It delivered high-end bass performance in a modest footprint, years before digital signal processing and powered designs made that common.

Conclusion and Legacy

The Infinity RS-II may not have the star power of Infinity's flagship systems. It combined a passive radiator with quality drivers and a well-tuned crossover. The result was a compact speaker with deep, articulate bass and clear, natural mids and highs, which few competitors could match at the time.

For vintage audio buyers who want a compact speaker with real bass and honest tonality, the RS-II is a solid choice. It rewards careful setup and quality amplification.

A well-preserved pair is worth picking up. With a little care, the Infinity RS-II can still hold its own next to digital audio and smart speakers.

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