Crossover Settings for PA Systems: Frequency Division Fundamentals

Crossover settings divide the audio spectrum between different speakers in a PA system, directing appropriate frequencies to speakers designed to reproduce them. Proper crossover configuration ensures each speaker operates within its capabilities while maintaining seamless frequency coverage.

Understanding Crossovers

Crossovers split the frequency spectrum using filters. A low-pass filter sends low frequencies to subwoofers; a high-pass filter sends higher frequencies to main speakers.

The crossover frequency defines where the split occurs. Both speakers contribute at this frequency; above and below, one speaker dominates.

The crossover slope determines how quickly each speaker’s response rolls off. Steeper slopes provide sharper separation; gentler slopes provide more overlap.

Main-to-Subwoofer Crossover

The crossover between main speakers and subwoofers typically falls between 80 and 120 Hz. This range suits most systems, though specific speakers may prefer different settings.

Setting the crossover too high sends midrange content to subwoofers, causing localization problems and reduced clarity.

Setting the crossover too low leaves a gap where neither mains nor subs contribute strongly, creating a hole in the bass response.

Slope Options

Slope is measured in dB per octave. Common slopes include 12 dB/octave (second-order), 18 dB/octave (third-order), and 24 dB/octave (fourth-order).

Steeper slopes provide sharper separation between drivers. This can protect speakers from frequencies they handle poorly.

Gentler slopes create more overlap at the crossover frequency. This can sound smoother but may cause phase issues or power handling problems.

High-Pass Filters on Mains

High-pass filters on main speakers remove low frequencies the mains cannot reproduce efficiently. This protects woofers and allows cleaner midrange.

Setting the high-pass at or slightly above the crossover point to subwoofers creates seamless handoff.

Even without subwoofers, high-pass filtering mains improves performance by eliminating frequencies they cannot reproduce well anyway.

Low-Pass Filters on Subwoofers

Low-pass filters on subwoofers remove midrange content they would reproduce poorly. Subwoofer drivers are not designed for mid-frequency reproduction.

Setting the low-pass at or slightly below the crossover point creates smooth transition to mains.

Some systems use steeper slopes on subwoofer low-pass than on main high-pass, providing additional protection against unwanted content reaching subs.

Powered Speaker Considerations

Powered speakers with built-in DSP often include preset crossover modes. Engaging “sub mode” or similar typically activates appropriate high-pass filtering.

When using powered speakers with matched subwoofers, use manufacturer-recommended crossover settings. These have been optimized for the specific speaker combination.

Manual adjustment may improve on presets for specific applications, but presets provide good starting points.

System Processor Crossovers

Outboard system processors (Lake, BSS, dbx DriveRack) provide precise crossover control. These sit between mixer and amplifiers in bi-amped or tri-amped systems.

Digital crossovers offer exact frequency selection, adjustable slopes, and phase control at the crossover point.

Analog crossovers in older systems provide similar function with less flexibility and precision.

Bi-Amping and Tri-Amping

Bi-amped systems use separate amplifiers for low and high frequencies in a two-way speaker. The crossover divides signal before amplification.

Tri-amped systems add a third frequency band—typically low, mid, and high. Each band has dedicated amplification.

Multi-amping provides more control and power headroom but requires more equipment and careful setup.

Phase at Crossover

Crossover filters introduce phase shift. At the crossover frequency, both speakers contribute with different phase relationships.

Proper crossover design accounts for phase alignment at the crossover point. Linkwitz-Riley crossovers provide aligned phase at crossover.

Misaligned phase at crossover creates a dip or peak in response. Polarity reversal on one speaker may help; delay adjustment may also be needed.

Choosing Crossover Frequency

Consult speaker specifications for recommended crossover frequencies. Manufacturers know their products’ capabilities.

General guidelines: 80-100 Hz for main-to-sub crossover in most music PA systems; higher for smaller mains, lower for larger.

Listen to the crossover region while adjusting. The smoothest, fullest sound indicates appropriate setting.

Verifying Crossover Settings

Measure frequency response across the crossover region. A smooth transition without peaks or dips indicates proper setup.

Walk the venue listening for consistent bass response. Poor crossover settings may sound different in different positions.

Pink noise testing reveals crossover anomalies. The crossover region should sound consistent with adjacent frequencies.

Common Problems

Gap at crossover: Not enough overlap between speakers. Lower the high-pass on mains or raise the low-pass on subs.

Peak at crossover: Too much overlap causing summation. Spread the crossover frequencies apart or adjust levels.

Hollow or thin sound: Phase issues at crossover. Try polarity reversal on one speaker or adjust delay for alignment.