Rolls SX21 Tiny Two-Way Active Crossover, 24 dB/Octave

Rolls SX21: A Tiny Two-Way Crossover for Bi-Amping

The Rolls SX21 is a compact two-way active crossover that splits a full-range signal into separate low and high bands for bi-amping, all in a chassis measuring 4.25 by 3.625 by 1.5 inches. A crossover divides the audio by frequency so that lows go to one amplifier and speaker and highs go to another, which is the foundation of a bi-amped system. The SX21 uses a steep 24 dB per octave slope and an adjustable crossover point from 50 Hz to 2.5 kHz, with independent level controls for each output. It connects on 1/4-inch unbalanced jacks and runs from an included external supply for low-noise operation. For small PA rigs, stage monitors, or install systems that need clean frequency division in a tiny box, the SX21 is purpose-built.

24 dB/Octave Division with an Adjustable Crossover Point

The SX21 divides the signal at 24 dB per octave with a crossover frequency adjustable from 50 Hz to 2.5 kHz. Crossover slope describes how sharply the filter separates the two bands, and 24 dB per octave is a steep slope that keeps low frequencies out of the high driver and vice versa with little overlap. A steep slope protects a compression driver or tweeter from damaging low-frequency energy and keeps the woofer from muddying the highs. The adjustable frequency lets you set the split point to match the drivers or speakers in your system, whether that is a subwoofer-and-mains setup or a two-way monitor. For a technician bi-amping a specific pair of speakers, that steep, tunable crossover point is what makes the system's two halves work together cleanly.

Independent Low and High Output Level Controls

The SX21 provides independent output level controls for its low and high bands, so you can balance the two amplifiers feeding your speakers. Because different drivers have different sensitivities, a woofer and a horn rarely play at the same loudness for a given input, and separate level controls let you match them. Setting the high and low outputs independently means you can dial in a flat, balanced response rather than being stuck with whatever the raw driver levels produce. That control lives right on the crossover, ahead of the amplifiers, so the adjustment is clean and repeatable. For anyone tuning a bi-amped rig by ear, independent band levels are the controls that get the balance right.

1/4-Inch I/O and a Low-Noise External Supply

The SX21 uses 1/4-inch unbalanced connections for its input, low output, and high output, presents a 10k ohm input impedance with a 1k ohm output impedance, offers +10 dBV of headroom, and runs from an included Rolls PS27 supply rated at 12 to 16 VDC, 150 mA. The 1/4-inch jacks match the connections on most compact mixers and power amplifiers, so the crossover drops into a small rig directly. Its input and output impedances are set to bridge a source and drive amplifiers without level loss. Running the crossover from an external supply keeps the power transformer's hum away from the audio circuitry, which is why the box stays quiet. For a compact bi-amp setup, that connector and power arrangement is straightforward to integrate.

For Bi-Amping Monitors, PA, and Install Systems

The SX21 is built for bi-amping small PA systems and stage monitors, splitting subwoofer and main frequencies in compact rigs, DJ and mobile sound setups, and install audio frequency division. As a mono two-way crossover, it handles one signal path, so a stereo system would use two, but for a mono monitor wedge or a mono sub feed it is exactly right. Its tiny chassis and included supply make it easy to tuck into a rack drawer or amp rack. The steep 24 dB slope gives it cleaner driver protection than gentler consumer crossovers. For anyone building a focused bi-amped rig where space is tight, the SX21 delivers professional frequency division in a very small box.