KLH Model 21 Speakers

The KLH Model 21 is a pair of passive bookshelf speakers introduced in 1968. KLH aimed to sell high-fidelity audio at an accessible price. Henry Kloss designed it around the acoustic suspension principle. It has a compact cabinet with a walnut veneer finish and a balanced sound. It was in production from 1968 to 1972.

Specifications

Feature	Specification
Manufacturer	KLH (Kloss Loudspeaker & Headphones)
Model	Model 21
Production Years	1968–1972
Type	Passive, 2-way bookshelf speaker
Design	Acoustic suspension
Driver Complement	1 x 5.25-inch woofer, 1 x 1-inch dome tweeter
Crossover	2nd-order network (exact frequency unknown)
Power Handling	Compatible with 10–60W amplifiers (typical use)
Impedance	Not officially documented (likely 8 ohms nominal)
Sensitivity	Not officially documented
Enclosure Finish	Walnut veneer with removable cloth grille
Dimensions (H×W×D)	13.5 × 7.5 × 7.5 inches (34.3 × 19.1 × 19.1 cm)
Weight	Approx. 14 lbs (6.4 kg) per speaker

Historical Context

KLH was founded in 1957 by Henry Kloss, Malcolm S. Low, and Josef Anton Hofmann. That's where the KLH acronym comes from. The company was known for combining scientific rigor with consumer-friendly design. The Model 21 built on earlier models like the Model 11 and Model 15, and it gave buyers a more compact option for smaller listening rooms.

Henry Kloss was a pioneer of acoustic suspension, originally developed in collaboration with Edgar Villchur at Acoustic Research. The design uses a sealed cabinet and an air spring behind the woofer. That improves low-frequency control and reduces distortion, which is especially useful in small enclosures. The Model 21 brought this technology to a broader audience in homes across America.

The Model 21 has a warm, natural sound and an attractive wood finish. Audiophiles and casual listeners alike favored it. It isn't as bass-heavy as the larger floor-standing models. It does deliver excellent midrange clarity and smooth high frequencies, which suits vocal and acoustic music.

Sound Characteristics

The Model 21 is warm and balanced, with its main strength in the midrange. The acoustic suspension design gives tight, controlled bass for its size. Deep sub-bass is limited by the compact cabinet. The dome tweeter gives smooth, non-fatiguing highs and avoids the harshness found in some contemporary designs.

These speakers work best with tube amplifiers or warm-sounding solid-state gear. They are not suited to high-volume or bass-heavy modern recordings unless you add a subwoofer. In intimate listening rooms they do well with jazz, classical, and vocal-centric genres.

Maintenance and Restoration Tips

Because of their age, most surviving KLH Model 21 speakers need some degree of restoration to perform at their best:

Foam Surround Replacement: The original foam surrounds on the woofers commonly degrade into dust after 40+ years. Replacing them with modern rubber or foam kits (available from specialty audio restoration suppliers) is essential for restoring bass response and preventing driver damage.

Crossover Capacitors: The electrolytic capacitors in the crossover network may have dried out or drifted in value. Replacing these with modern film or low-ESR electrolytic capacitors can significantly improve clarity and reliability.

Grille Fabric: The original cloth grilles often show wear or discoloration. Reproduction grilles or custom replacements using acoustically transparent fabric can restore both appearance and function.

Cabinet Care: Clean the walnut veneer with a soft, dry cloth. Avoid harsh polishes; use a mild wood cleaner if needed. Check for loose joints or veneer lifting, which can be repaired with wood glue and clamping.

Speaker Terminals: Inspect the binding posts for corrosion. Clean with contact cleaner or replace with modern terminals for better connectivity.

Collectibility and Market Value

The KLH Model 21 has moderate collectibility, rated around 6/10 among vintage audio enthusiasts. It is not as rare as the Model 1 or Model 8. It is still a respected example of KLH's design approach and Henry Kloss's engineering.

A pair of Model 21 speakers typically sells for $100 to $300 today, depending on condition, originality, and whether they've been restored. Fully restored pairs with upgraded foam and capacitors often command higher prices, especially when sold with original packaging or documentation.

Conclusion

The Model 21 is a compact, science-driven design from the late 1960s with an elegant finish. Vintage audio fans and first-time restorers both still seek it out. With proper maintenance, it can deliver decades more of listening.

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