Infinity RS-5B: The Compact Innovator with Big Bass

The Infinity RS-5B is a compact bookshelf speaker from the late 1970s, when hi-fi was moving from console stereos to component systems. It is less documented than its larger siblings, the RS-1B and the IRS series. Its selling point was extended bass and high efficiency in a small enclosure, and it got there with a passive radiator.

A Brief Historical Context

Introduced in 1977, the RS-5B was part of Infinity's RS (Reference Standard) series, a line meant to bring high-performance speaker technology to more affordable, space-conscious setups. Most compact speakers of the time struggled with bass. Infinity applied ideas from its larger, more expensive designs to a bookshelf model. The RS-5B followed the RS-1B and shared its design approach, most notably passive radiator technology instead of a traditional ported or sealed enclosure.

Infinity was founded in 1968 by Arnie Nudell and Cary Christie. Its early work included servo-controlled subwoofers and large multi-driver arrays. The RS-5B is modest in scale, but it gives deep bass extension without a powered subwoofer, which was rare in compact speakers of the era.

Technical Specifications

Specification	Detail
Model	RS-5B
Manufacturer	Infinity Systems, Inc.
Year Introduced	1977
Type	2-way, passive radiator bookshelf speaker
Driver Complement	1 x 5.25" woofer, 1 x 1" dome tweeter
Passive Radiator	1 x 5.25" (bass radiator, tuned for low end)
Frequency Response	55 Hz – 20 kHz (±3 dB)
Sensitivity	89 dB (1W/1m)
Nominal Impedance	8 ohms (compatible with most vintage amps)
Recommended Power	15 – 100 watts
Crossover Frequency	~3.5 kHz
Enclosure Type	Reflex (passive radiator)
Dimensions (HxWxD)	13.5" x 8" x 9.5" (34.3 x 20.3 x 24.1 cm)
Weight	~18 lbs (8.2 kg) per speaker
Finish Options	Walnut vinyl veneer, black ash (common)

Sound Characteristics and Performance

The Infinity RS-5B sounds balanced and dynamic for its size. Its most notable trait is the extended bass response, which reaches down to 55 Hz - a good figure for a bookshelf model without a port or powered sub. The large 5.25" passive radiator on the front baffle does the work. It acts like a port, but without "chuffing" noise or port turbulence.

The 5.25" polypropylene cone woofer handles midbass and lower midrange, and the 1" soft dome tweeter handles the highs. The crossover hands off between the drivers for a coherent, natural soundstage.

In practice, the RS-5B does well with acoustic jazz, vocal recordings, and classic rock. Its efficiency is 89 dB, so it pairs well with lower-powered tube amplifiers and vintage solid-state receivers from the 1970s and 80s. It won't fill a large room. Bedrooms, offices and secondary listening rooms suit it better. With a quality preamp and amp, it reveals a good amount of detail and spatial imaging.

Notable Features and Innovations

The passive radiator was one of the RS-5B's most forward-thinking features. A ported speaker can suffer from air noise at high volumes. A passive radiator instead moves in response to the internal air pressure created by the active woofer. That allows deeper bass tuning in a smaller cabinet. The technique is now common in modern Bluetooth speakers and subwoofers, but it was rare in 1970s bookshelf designs.

Another strength is the 8-ohm impedance, which suits a wide range of vintage and modern amplifiers. Many compact speakers of the era dropped to 4 ohms, which limited amplifier choices. The RS-5B's stable load works fine with older gear.

The cabinet is not as massive as Infinity's flagship models, but it is solid for its class. It uses medium-density fiberboard (MDF) with internal bracing to reduce resonance. The passive radiator fires from the front, so the speaker doesn't need space from the wall the way rear-ported designs do.

Common Issues and Maintenance

Like all vintage speakers, the RS-5B needs some maintenance. The most common problem is aging of the woofer surround, typically foam. Over time foam dries out, cracks and disintegrates, leading to distorted bass or complete failure. Foam replacement kits are widely available and fairly easy to install with basic tools and glue.

The tweeter dome is generally durable, but an overdriven speaker or one exposed to moisture may have tears or distortion. Original tweeters can be hard to source, though some modern equivalents offer compatible performance.

Crossover components, particularly electrolytic capacitors, may degrade over decades. If the sound turns thin or harsh, a crossover inspection or recapping by a qualified technician can restore clarity and balance.

Clean dust and grime off the cabinet with a soft, slightly damp cloth. Avoid harsh chemicals, especially on the vinyl veneer, which can crack or peel if improperly treated.

Current Market Value and Collectibility

The Infinity RS-5B is not a high-profile collector's item like the IRS V or the EMPIRE series, but it has a loyal following among vintage audio enthusiasts. In good working condition, a pair typically sells for $150 - $300, depending on finish, originality, and whether the foam surrounds have been replaced.

Fully restored pairs with new foam and recapped crossovers may bring slightly higher prices, especially with original grilles and documentation. It isn't a "blue chip" vintage speaker, but it offers excellent value for money and is an accessible entry point into the Infinity lineup.

Its compact size and walnut finish also make it a popular choice for vintage-themed setups or secondary systems where space is limited.

Conclusion and Legacy

The RS-5B shares the engineering philosophy of its larger siblings: maximize performance within physical constraints. Infinity applied passive radiator technology to a compact bookshelf format and got deep, articulate bass and clear, detailed highs.

Today, the RS-5B stands as a testament to late-1970s American speaker innovation. It’s a speaker that rewards careful restoration and thoughtful pairing with vintage electronics. For the audiophile who values both sound quality and historical significance in a modest footprint, the Infinity RS-5B remains a quietly impressive choice.

A well-preserved pair has a walnut veneer and a bigger sound than its size suggests.

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