The KLH Model Four is a 3-way acoustic-suspension floorstander that condenses decades of Henry Kloss engineering philosophy into a slim, real-wood cabinet. For the experienced listener, it represents something increasingly rare: a modern speaker that refuses the easy path of a ported box and instead commits fully to sealed-enclosure discipline. This is a design built for accuracy first, with bass that stays composed at volume and a top end you can tailor to your room. In the sections below we will take the Model Four apart driver by driver, examine its crossover and cabinet engineering, decode its specifications, and place it precisely within the current KLH lineup.
Core Design Philosophy
What is acoustic suspension, and why does KLH use it?
Acoustic suspension is a sealed-box design in which the trapped air inside the cabinet acts as a spring that controls the woofer's motion, and KLH uses it because it delivers exceptionally tight, low-distortion bass. In a sealed enclosure there is no port, so the air behind the cone becomes a restoring force that works with the driver's own suspension. The practical result is bass that is more accurate and better controlled than a comparable vented design, and that stays clean even when you push it hard. You also get deeper extension from a smaller cabinet than a ported box could manage at the same size.
The trade-off is sensitivity. Because the air spring resists cone motion, an acoustic-suspension speaker gives up a little efficiency compared to a ported alternative, which means it rewards a capable amplifier. This is not a flaw so much as a design choice, and it is central to why the Model Four sounds the way it does. KLH helped popularize this approach in the late 1950s, and it remains the defining trait of the brand's sound.
Why does the sealed box matter for how the Model Four sounds at high volume?
The sealed box matters at high volume because the air-spring loading keeps the woofer under mechanical control right up to its excursion limits, preventing the loose, overhung bass that vented boxes can exhibit near their tuning frequency. A ported enclosure unloads the cone below its port tuning, which can allow uncontrolled excursion and distortion. The Model Four's sealed alignment avoids that failure mode entirely. The bass simply rolls off gently and predictably, so what you hear stays tight and pitch-accurate as levels climb toward the speaker's 108 dB maximum SPL.
The Drivers
What is the woofer made of, and how is it built?
The woofer is an 8 inch pulp-paper cone with a reverse-roll rubber suspension. Treated paper pulp is a light, well-damped material that KLH voices for a natural, uncolored tone, and it is a deliberate choice over stiffer synthetic cones that can add their own coloration. Paper's self-damping means fewer stored-energy resonances in the passband, which contributes to the natural midbass character. The reverse-roll rubber surround is oriented specifically to control cone motion with precision and lower distortion, which pairs perfectly with the acoustic-suspension loading behind it.
What does the 4 inch midrange contribute?
The 4 inch midrange handles the critical band where voices and instruments live, and it is built from the same treated pulp-paper cone with a reverse-roll rubber suspension as the woofer. Using matched cone material across the woofer and midrange gives the Model Four tonal continuity through the crossover region, so there is no jarring shift in character as the music moves from the lower registers up into the presence band. A dedicated midrange driver in a 3-way design also relieves the woofer of duty above the lower crossover point, letting the 8 inch cone focus solely on bass while the 4 inch cone reproduces the midrange with lower distortion and better dispersion.
What kind of tweeter does the Model Four use?
The Model Four uses a 1 inch aluminum dome tweeter. The metal dome is light and rigid, a combination that pushes the dome's breakup modes well above the audible band and yields extended, detailed treble. An anodized aluminum dome resists the flexing that would color the highs, so transients arrive cleanly and high-frequency detail stays intact. Paired with the tunable Acoustic Balance Control, this tweeter gives the Model Four a top end that is both revealing and adjustable to taste.
Tuning, Crossover, and Connections
What does the Acoustic Balance Control do?
The Acoustic Balance Control is a 3-position switch on the speaker that raises or lowers the high-frequency level in small steps, letting you tune the brightness to your room and your taste. This is a KLH signature carried over from the original Model Five, and it is genuinely useful in practice. A room with hard floors, glass, and bare walls can sound bright and fatiguing, while a heavily furnished room with thick carpet and curtains can sound dull. The Acoustic Balance Control lets you compensate for either condition at the speaker itself rather than relying on tone controls or EQ upstream.
Where does the Model Four split the frequencies, and why does that matter?
The Model Four crosses over at 380 Hz and 2,500 Hz, dividing the workload between the woofer, midrange, and tweeter. The crossover is the internal filter network that routes each part of the signal to the driver best suited to reproduce it. The lower crossover at 380 Hz hands off from the 8 inch woofer to the 4 inch midrange near the bottom of the vocal range, keeping the woofer out of the midrange where its size would limit dispersion. The upper crossover at 2,500 Hz passes the top octaves to the aluminum dome tweeter. These points are chosen so each driver operates within its comfort zone, which minimizes distortion and keeps the tonal handoff seamless.
What connections does the Model Four offer?
The Model Four uses 5-way gold-plated binding posts. Five-way posts accept banana plugs, spade lugs, pins, and bare wire, so they work with essentially any cable termination you already own. The gold plating resists corrosion at the contact surface, which preserves a clean, low-resistance connection over the long term. This is a single-wire configuration matched to the speaker's internal crossover.
Cabinet and Physical Design
How is the cabinet built, and what are its dimensions?
The cabinet is a sealed slim floorstander measuring 32.2 x 13 x 10.9 inches with its riser base, or 26 inches tall without the riser. Because acoustic suspension depends on a completely airtight enclosure, cabinet integrity is not optional; any leak would compromise the air spring that controls the woofer. The sealed construction is what allows the trapped air to function as a precise restoring force. The slim footprint keeps the Model Four visually unobtrusive while still housing an 8 inch woofer, which is a direct benefit of the sealed alignment's efficient use of internal volume.
What does the slant-riser base do?
The slant-riser base is an included angled plinth that tilts the speaker back slightly to time-align the drivers at ear height while adding stability. Tilting the baffle back adjusts the relative arrival times of the sound from the woofer, midrange, and tweeter so that they reach a seated listener more coherently. The added footprint also lowers the effective center of gravity and widens the base, making the slim tower more stable on carpet or hard floors.
What finishes and grille options are available?
The Model Four comes in three finish combinations: English Walnut with a Stonewash grille, Black Ash with a Grey grille, and White Oak with a Black grille. Each pairs a real-wood or textured cabinet with a coordinated magnetic knit grille. The grille attaches magnetically, so there are no visible mounting holes on the baffle when it is removed, and it can be taken off cleanly for critical listening or left on for a finished look.
Reading the Specifications
What does a sensitivity of 88 dB mean in practice?
A sensitivity of 88 dB (measured at 2.83 V and 1 m) means the speaker produces 88 decibels of output one meter away when fed a standard reference input, and this tells you how loud it plays for a given amount of power. For an acoustic-suspension design this is a healthy figure, since sealed boxes tend to run a touch lower in efficiency than ported ones. In practice, 88 dB is moderate, so the Model Four appreciates an amplifier with real power in reserve to reach its 108 dB maximum SPL cleanly and to keep dynamic peaks effortless. This is the acoustic-suspension trade-off in action: you give up a little sensitivity in exchange for tighter, more accurate bass.
What does the 6 ohm nominal impedance (3.5 ohm minimum) tell you about amplifier matching?
The 6 ohm nominal impedance with a 3.5 ohm minimum tells you the electrical load the speaker presents to the amplifier, and it means you want an amplifier comfortable driving loads that dip below 4 ohms. Nominal impedance is an average figure; the 3.5 ohm minimum is the more demanding number, since that is where the amplifier is asked to deliver the most current. An amplifier with a stable power supply that increases output as impedance drops will handle the Model Four with ease. Combined with the 88 dB sensitivity, the message is consistent: this speaker rewards a robust, current-capable amplifier rather than a modest one.
What does the frequency response of 46 Hz to 20 kHz tell you?
The frequency response of 46 Hz to 20 kHz (plus or minus 3 dB) tells you the range the speaker reproduces within a tight tolerance, with the lower number indicating how deep the bass extends. Reaching down to 46 Hz from a sealed slim tower is a strong result and covers the vast majority of musical fundamentals, including electric bass and most kick drum weight. Just as important is the plus or minus 3 dB tolerance, which signals a genuinely flat response across the band rather than a peaky, hyped tuning. The gentle sealed-box roll-off below 46 Hz also tends to integrate well with room gain, often reinforcing the deepest notes rather than fighting them.
What do the power handling numbers mean for real use?
The power handling of 150 watts continuous and 600 watts peak means the Model Four can absorb substantial sustained power and handle brief musical transients well beyond that. The continuous figure describes what the drivers and crossover can dissipate over time, while the peak figure covers the short bursts that music actually contains. For real use, this headroom means you can pair the Model Four with a genuinely powerful amplifier without concern, which is exactly what its moderate sensitivity and demanding impedance minimum call for.
Room Placement and System Matching
How should you position the Model Four in a room?
You should position the Model Four with the slant-riser base engaged so the drivers time-align toward your listening height, then use the Acoustic Balance Control to fine-tune the top end to your room. Because it is a sealed design with a gentle low-end roll-off, the Model Four is more forgiving of near-wall placement than a ported speaker, which can boom when its port is close to a boundary. Placing it moderately close to the front wall can even add welcome low-frequency reinforcement. Start with a modest toe-in toward the listening position, then set the Acoustic Balance Control to taste: lower it in a live, reflective room, raise it in a heavily damped one.
Where the Model Four Sits in KLH's Lineup
How does the Model Four fit within the current KLH range?
The Model Four sits as a slim 3-way floorstander within a KLH range that also includes the Model Three, the Model Five, and the Model Seven, all built on the same acoustic-suspension foundation. KLH, founded in 1957 by Henry Kloss, is one of the storied American loudspeaker names, and modern KLH Audio revives these sealed-box designs with contemporary drivers and cabinets. The Acoustic Balance Control the Model Four carries traces directly back to the original Model Five, while the larger Model Seven takes the sealed philosophy further with its woofer housed in a dedicated sealed sub-enclosure that isolates it from the midrange. The Model Four's appeal is that it delivers that lineage in a genuinely slim tower, offering full 3-way performance and real acoustic-suspension bass in a form that fits real rooms.
Why does this heritage matter for how the Model Four performs and lasts?
This heritage matters because the acoustic-suspension engineering is precisely why the Model Four sounds and measures the way it does, and it is a proven approach with more than six decades behind it. The sealed-box discipline, the well-damped paper cones, the tunable top end, and the airtight cabinet all descend from a design tradition built around accuracy and longevity. That confidence is reflected in the 10 year warranty, an unusually long term that speaks to how the speaker is engineered to last. For the experienced listener who values tight, honest bass and a top end they can dial in, the Model Four is a thoroughly modern expression of a classic and enduring idea.