KLH Model Nine (1959–1979)

Name: KLH Model Nine
Brand: KLH

A floor-to-ceiling window into sound, so transparent it disappears—until the bass hits and you remember it’s not magic, it’s engineering.

Overview

Standing nearly six feet tall but barely thicker than a hardcover book, the KLH Model Nine doesn’t enter a room—it redefines it. These aren’t speakers you place on stands; they’re architectural elements you position like sentinels, flanking your listening chair with the quiet authority of modernist design. When you walk into a space where a pair of Nines are properly set up, the first thing you notice isn’t their size, but the silence between them—until they play, and suddenly the air itself seems to come alive with detail so fine it feels like you’re eavesdropping on the recording session. This is the promise of full-range electrostatics, and in 1959, the Model Nine was the first to deliver it without compromise.

Born from the mind of Arthur Janszen, a pioneer in high-frequency electrostatic design, the Model Nine was KLH’s flagship statement at a time when most companies were still wrestling with cone distortion and box coloration. Janszen had already made waves with his Z-130 tweeter array, but the Nine was different—it wasn’t a hybrid or an add-on. It was a complete, full-range electrostatic panel, the first of its kind to cover the entire audible spectrum without relying on a conventional dynamic woofer. That’s not just rare for the era—it’s remarkable even by today’s standards. Each panel houses ten vertically stacked electrostatic "woofers" and a single 4-inch square electrostatic tweeter at the top, all driven by a single transformer-based network that elegantly handles the handoff around 800 Hz. There’s no traditional crossover in the modern sense, just a passive, inductive divide that keeps things clean and coherent.

The result is a speaker that doesn’t “project” sound so much as it “releases” it—dipole radiation at its most natural, with a wide, airy dispersion that avoids the forward glare of box speakers. The highs are famously smooth, extending well beyond 20 kHz without a hint of grain, while the bass reaches down to 40 Hz with startling authority for a design with no enclosure. That bass isn’t boomy or loose; it’s taut, articulate, and shockingly dynamic when fed with the right amplifier. And because the panels are so thin and wide, they create a soundstage that seems to float in space, with imaging precision that still impresses decades later.

But let’s be clear: the Model Nine isn’t for everyone. It demands space—both physical and electrical. These are power-hungry speakers with a nominal 16-ohm load that dips even higher at resonance, meaning they need amplifiers with robust output transformers and solid current delivery. They also require outboard power supplies (one per panel) to generate the high voltage needed to charge the stators. And while their looks are undeniably striking, their size and open-back design mean they need to be placed well away from walls, often several feet, to breathe properly. You don’t just buy a pair of Nines—you commit to them.

Specifications

Manufacturer	KLH
Production Years	1959–1979
Original Price	$2,000 per pair (1959)
Type	Full-range electrostatic loudspeaker
Frequency Response	40 Hz – 30 kHz
Nominal Impedance	16 ohms
Maximum Impedance	30 ohms
Amplifier Power Requirement	50–75 watts per channel minimum
Dimensions (H × W × D)	70" × 23.5" × 2.875"
Weight	Approx. 40 lbs per panel
Driver Complement	10 electrostatic woofers, 1 electrostatic tweeter (4" × 4")
Crossover	Transformer-coupled, ~800 Hz
Power Supply	External high-voltage supply required (one per speaker)
Grille Material	Bouclé fabric
Frame Material	Hardwood (walnut or mahogany finish)
Recommended Room Size	Medium to large (minimum 12' × 15')
Dispersion	Dipole (front and rear radiation)
Years Since Discontinuation	45+ years

Key Features

The Transformer-Coupled “Crossover-Less” Design

While technically a two-way system, the Model Nine avoids traditional capacitors and inductors in its crossover. Instead, it uses a custom transformer with multiple windings on a shared core to split the signal between the woofer panels and the tweeter. This isn’t just a clever trick—it’s a fundamental part of the speaker’s coherence. Because the transformer couples the signals magnetically rather than electrically, it minimizes phase distortion and preserves transient detail. The handoff at 800 Hz is so seamless that many listeners report hearing a single, unified source rather than two distinct drivers. That’s rare even in modern high-end speakers, and in the 1960s, it was revolutionary.

Dipole Radiation and Room Integration

The Model Nine radiates sound from both the front and back of the panel, creating a dipole pattern that interacts heavily with the room. This isn’t a speaker you can shove into a corner or treat like a conventional box. It needs space—especially behind it—to allow the rear wave to develop. When set up correctly, this dipole behavior eliminates cabinet resonances and reduces early reflections, resulting in a more natural, open sound. But get it wrong, and you’ll lose bass impact or create nulls at the listening position. Owners report that toe-in, distance from walls, and even carpet thickness can dramatically affect performance. It’s not fussy—it’s precise.

High-Voltage Outboard Power Supplies

Each speaker requires its own external power supply, which generates the 5,000+ volts needed to charge the stators and polarize the diaphragm. These supplies are not optional—they’re integral to operation. While this adds complexity, it also isolates the high-voltage circuitry from the audio signal path, reducing noise and interference. The supplies themselves are relatively simple, housing selenium rectifiers (in originals), step-up transformers, and filtering components. Over time, these can fail—especially the selenium diodes, which degrade and can emit a rotten-egg smell when they go. Modern refurbishments typically replace them with silicon diodes, a critical upgrade for reliability.

Historical Context

The late 1950s were a golden age for electrostatic experimentation. Companies like Quad were pushing the boundaries with designs like the ESL-57, but they were limited to midrange and treble, relying on dynamic woofers for bass. The KLH Model Nine changed that. As the first full-range electrostatic speaker to achieve commercial production, it represented a leap in both ambition and execution. Arthur Janszen, who had already proven his mastery of high-frequency electrostatics, joined KLH after the company acquired his lab, and the Nine became his magnum opus. It wasn’t just a speaker—it was a statement that high fidelity could be both scientifically rigorous and aesthetically bold.

At a time when most hi-fi gear was shrinking into bookshelf cabinets, KLH went vertical. The Nine stood in stark contrast to the acoustic-suspension speakers Henry Kloss had made famous at Acoustic Research. Where the AR-3 was compact and self-contained, the Nine was expansive and architectural. It competed not just with other speakers, but with the idea of what a speaker should be. Priced at $2,000 per pair in 1959—roughly $20,000 today—it was never meant to be mass-market. Instead, it targeted serious audiophiles and design-conscious buyers who wanted both sonic transparency and visual impact. Only about 5,000 pairs were ever made, a number that reflects both its complexity and its niche appeal.

The Nine’s legacy extends far beyond its production run. It’s been called one of the 12 most significant speakers of all time, and its influence can be seen in later electrostatics from Sound Lab, MartinLogan, and even modern reissues from KLH itself. When David Kelley relaunched the brand in the 2010s, one of his first moves was to reintroduce the Model Nine—not as a nostalgia piece, but as a faithful recreation for a new generation of listeners.

Collectibility & Value

Today, a pair of original KLH Model Nines in working condition is a rare find—and a serious investment. Prices vary widely based on condition, completeness, and whether the electronics have been refurbished. Unrestored pairs with original power supplies and minor cosmetic wear typically sell between $2,500 and $4,000. Fully restored units, especially those serviced by specialists like JansZen Audio, can command $8,000 to $10,000 or more. Given that a brand-new reissue from KLH retails for $12,499 per speaker, the vintage market holds strong.

The biggest concern for buyers is age-related failure. After 40 to 60 years, several components are prone to degradation. Selenium diodes in the power supplies are the most common point of failure—they can short, open, or leak toxic residue. Carbon composition resistors in the transformer network drift in value over time, affecting frequency balance. The original PVDC diaphragm material stiffens with age, reducing bass output and lowering the low-frequency limit from 40 Hz to as high as 90–100 Hz in neglected units. Bakelite terminal boards develop leakage paths, and the original vinyl wiring loses insulation integrity.

A proper restoration isn’t a simple refoam job—it’s a full-system overhaul. Reputable shops like JansZen Audio offer multi-tier refurbishments that include replacing diodes, resistors, and wiring; cleaning and re-membraning the panels; and upgrading terminal blocks. Some even apply protective acoustically transparent films to prevent future contamination from dust and smoke. These services are expensive—$7,000 to $10,000—but they restore the speaker to (or beyond) its original performance.

For buyers, the advice is clear: never purchase a pair without verifying functionality. Ask for sound tests, check for arcing or buzzing, and inspect the power supplies for corrosion or odor. If the seller can’t demonstrate that they work, assume they don’t. And if you’re not ready to invest in a full restoration, consider whether the visual appeal is worth the cost—because these are not “plug and play” speakers. They’re heirlooms, projects, and statements—all at once.