Line Array Tuning: A Practical Measurement Guide

A line array works by coupling the output of multiple vertically stacked elements to form a coherent wavefront. When the element spacing is less than the wavelength, the array produces a cylindrical wave that drops only 3 dB per doubling of distance (versus 6 dB for a point source). This cylindrical behavior enables a line array to project sound over longer distances with more even coverage than a conventional speaker.

The coupling is frequency-dependent. At low frequencies where wavelengths are long relative to the array length, the array behaves as a point source. At mid and high frequencies, the array narrows its vertical coverage and achieves cylindrical behavior. The transition frequency depends on the array length and element spacing.

Every major line array manufacturer provides prediction software (d&b ArrayCalc, L-Acoustics Soundvision, JBL Performance Manager, etc.) that models the array's coverage based on venue geometry. Input the venue dimensions, audience areas, and array hang point. The software calculates optimal splay angles, delay shading, and EQ per zone.

Prediction software provides the starting point, not the final answer. Real-world conditions (temperature gradients, humidity, audience fill, venue surfaces) differ from the model. Measurement verifies and refines the prediction.

After flying the array with the predicted settings, measure at three critical positions: front of audience (closest row), center of audience (approximately halfway), and rear of audience (farthest row). At each position, capture a transfer function measurement using SonaVyx with pink noise as the source signal.

Compare the three measurements overlaid. The frequency response above 200 Hz should be within plus or minus 3 dB across all positions. If the front row is significantly brighter than the rear, the bottom splay angles may be too tight (directing high-frequency energy over the front rows). If the rear position has excessive high-frequency rolloff, the upper zone may need a high-frequency shelf boost to compensate for air absorption.

Check coherence at each position. Low coherence (below 0.7) indicates that the measurement is contaminated by noise or reflections, and EQ adjustments at those frequencies will not produce predictable results. Focus EQ corrections on frequency ranges with high coherence.

Apply EQ corrections per zone using the array processor. Start with the upper zone, which covers the farthest audience positions. Apply a high-frequency shelf boost of 1-3 dB per zone to compensate for air absorption and distance. Apply low-mid cuts if room reflections are adding energy in the 200-500 Hz range.

For sub integration, measure the combined response of the subwoofer array and the line array through the crossover region (typically 60-120 Hz). Adjust sub delay until the combined response shows smooth summation without a dip or peak at crossover. Check phase alignment using the SonaVyx phase display: the sub and array should be within 90 degrees of each other at the crossover frequency.

After all adjustments, re-measure at the three primary positions plus two additional side positions to verify lateral coverage. Store all traces in SonaVyx for documentation. Export the before and after measurements as FRD files for inclusion in the system tuning report.

Document the final settings: splay angles per box, delay shading values, EQ per zone, sub delay, and crossover frequency. This documentation enables faster setup at the next event in the same venue and provides a reference for troubleshooting.