Setting Crossover Frequencies

💡 Measurement Tip: Take SLM measurements at consistent positions—typically at the primary listening position or at a standardized measurement position like 1 meter from the speaker. Consistent measurement positions ensure comparisons between measurements are valid and meaningful.

Timing Alignment

Timing alignment ensures that sound from different speaker components arrives at the listener simultaneously. When drivers are at different physical distances or have different acoustic centers, delaying the closer driver or advancing the farther driver creates proper alignment.

Acoustic center is the effective point from which each speaker radiates sound. For cone drivers, this is typically slightly behind the cone due to the voice coil and motor structure. For horn-loaded drivers, the acoustic center is at the horn mouth. Different driver types have different acoustic center positions, which must be accounted for in time alignment.

Distance measurement determines initial time alignment by measuring the physical distance between each driver's acoustic center and the listener (or reference microphone). The formula delay (ms) = distance (feet) × 0.88 provides the initial delay setting, with adjustments made based on measured results.

Impulse response analysis using measurement software reveals the actual time arrival of each speaker component at the measurement position. The impulse response shows a peak at the arrival time of the direct sound from each driver, allowing precise delay adjustment to align arrivals.

Polarity verification should accompany timing alignment. Drivers should have correct polarity (moving forward together at the crossover frequency) before time alignment adjustments. Polarity inversions can cause apparent time arrival differences that look like timing problems but are actually phase problems.

Common Crossover Frequencies

Standard crossover frequencies have evolved based on speaker driver capabilities, acoustic requirements, and practical experience. These common settings provide reliable starting points for most systems.

80 Hz is the most common subwoofer crossover frequency, recommended by THX for home theater and widely used in professional audio. This frequency keeps bass content away from smaller main speakers while allowing subwoofers to blend seamlessly with speakers that have reasonable low-frequency extension.

100-120 Hz crossover frequencies are common in larger PA systems where subwoofers and main speakers need clear separation. This higher crossover frequency keeps more low-frequency content in the main speakers (which may have better pattern control in this range) while the subwoofers handle only the deepest bass.

2-3 kHz is the most common crossover between midrange drivers and high-frequency compression drivers. This range falls in a frequency region where both driver types can perform well and where human hearing is most sensitive, making seamless integration critical.

4-5 kHz crossover frequencies are used when high-frequency tweeters need protection or when midrange drivers have limited high-frequency capability. The tradeoff is potential spatial shift if the tweeter is physically separated from the midrange driver.

Subwoofer Crossover Settings

Subwoofer crossover settings require attention to integration with main speakers and the specific bass content of the program material.

Crossover slope determines how sharply the subwoofer output attenuates above the crossover frequency. Steeper slopes (24 dB/octave) provide more complete isolation between subwoofer and main speakers but create more phase interaction in the crossover region. Gentler slopes (12 dB/octave) create more gradual transition but may allow localization of the subwoofer if crossover frequency is set too high.

Phase adjustment on subwoofers affects how well they sum with main speakers in the crossover region. Setting subwoofer phase to match the acoustic crossover slope of the main speakers typically produces the smoothest summation. Fine-tuning phase while observing the combined response reveals the setting that minimizes cancellation.

Low-pass filter settings on subwoofers control the upper frequency limit. Some subwoofers offer fixed frequencies (common in passive systems), while others provide adjustable low-pass filters. The low-pass setting should be high enough to allow bass instruments to sound natural while low enough to prevent localization of the subwoofer.

High-pass output on some subwoofers allows connecting to main speakers via line outputs, effectively creating an active crossover in the subwoofer that feeds the main speakers without bass content. This approach places the crossover in one convenient location with consistent adjustment.

Verification and Fine-Tuning

Initial crossover settings are starting points that require verification and refinement based on actual measurements and listening tests.

Listening tests using familiar music with prominent bass content reveal how well the crossover integration works perceptually. The subwoofer should not be localizable as a separate sound source. Bass notes should sound continuous whether they come from subwoofers or main speakers.

Measurement verification using SLM or more detailed measurement systems confirms smooth frequency response through the crossover region. Any peaks or dips exceeding 3 dB should be addressed through crossover frequency, level, or phase adjustment.

Program material testing across different genres and recording styles reveals whether the crossover settings work well universally or only for specific material. Settings optimized for one type of music may not work well for others, requiring compromise or adjustable settings that can accommodate different program types.