Beyond the Sweet Spot: Solving the "Comb Filtering" Crisis in Home Cinema

In the architecture of a home theater, the center channel is the keystone. It carries approximately 70% of a film’s audio data, including almost all dialogue and center-stage action. Yet, it is also the component most prone to a fundamental acoustic failure known as “Comb Filtering” or “Lobing.”

For decades, the industry standard for center speakers has been the MTM design (Midrange-Tweeter-Midrange). While aesthetically symmetrical and easy to place under a TV, this horizontal arrangement defies the laws of physics. When two woofers play the same frequency simultaneously, their sound waves interact. Directly in front of the speaker (on-axis), these waves sum perfectly. However, if you move just 15 to 20 degrees to the left or right—sitting on the other end of the couch—the distance from each woofer to your ear changes. This path length difference causes the waves to arrive out of phase, cancelling each other out at specific frequencies.

The result? The “Sweet Spot” becomes a “Sweet Chair.” Everyone else hears muddy, hollow dialogue.

The Klipsch RC-64 III is not merely a louder speaker; it is an engineered rebuttal to this flaw. By utilizing a sophisticated 2.5-Way Tapered Array Crossover, it maintains the output capability of four drivers while mimicking the dispersion characteristics of a single point source. This article dissects the electro-acoustic mechanisms that allow this flagship speaker to break the curse of horizontal directionality.

The Tapered Array Solution: Engineering Out Interference

To understand the solution, we must look at the driver configuration. The RC-64 III features four 6.5” Cerametallic woofers. In a basic design, all four would play the same frequencies up to the crossover point with the tweeter. This would create a disaster of interference patterns, narrowing the listening window to a sliver.

Klipsch employs a 2.5-way network to solve this.

1. The Inner Pair: The two woofers flanking the horn cover the bass and the critical midrange frequencies, blending seamlessly with the compression driver.
2. The Outer Pair: The two outermost woofers are utilized primarily for bass reinforcement. The crossover network rolls them off at a much lower frequency than the inner pair.

Why does this matter?
By limiting the higher frequencies to only the inner drivers, the effective distance between the sound sources is reduced at those wavelengths. This prevents the destructive interference that causes frequency dips (lobing) in the vocal range. The outer drivers simply add weight and impact to explosions and deep scores without muddying the delicate phase relationship of human speech.

This “Tapered Array” technique allows the RC-64 III to offer the massive dynamic slam of a large cabinet while retaining the wide, even dispersion of a smaller, more precise monitor. Whether you sit dead center or on the wing, the spectral balance remains consistent.

Controlled Directivity: The Tractrix Horn Advantage

While the crossover manages the woofers, the high frequencies are governed by the 1.75” Titanium Compression Driver mated to a 90° x 90° Tractrix Horn.

In standard dome tweeter designs, sound radiates in a wide hemisphere. This sends significant energy towards the ceiling and floor. These “early reflections” bounce back to the listener slightly later than the direct sound, smearing intelligibility and collapsing the soundstage.

The Klipsch solution is Controlled Directivity. The Tractrix geometry acts as an acoustic lens, focusing the sound energy specifically into the listening area (90 degrees horizontal and vertical).

• Acoustic Impedance Matching: The horn acts as a transformer, matching the high pressure at the driver surface to the low pressure of the room air. This is the secret behind the speaker’s staggering 99 dB sensitivity. The driver barely needs to move to produce reference-level volumes, resulting in ultra-low distortion.
• Reduced Room Interaction: By limiting floor and ceiling reflections, the RC-64 III takes the “room” out of the equation. You hear the direct signal from the movie mix, not the echo of your drywall.

Combined with the linear travel suspension (LTS) of the titanium diaphragm, this system ensures that sibilants (the “s” and “t” sounds) are crisp and defined, never harsh. This mechanical precision creates a center channel that projects dialogue with the authority of a commercial cinema screen, anchoring the experience regardless of the chaos happening in the surround channels.