Festival Sound System Requirements: Planning and Measurement

Festival audience areas are typically divided into coverage zones: the main floor (0-50m from stage), mid-field (50-100m), and rear-field (100m+). Each zone has different SPL targets and may require different speaker systems. The main PA covers the first 50-60 meters. Delay towers extend coverage beyond that.

Map the audience area and identify the target SPL at each zone. A common target is 105 dB LAeq at the mix position (typically 25-40m from the stage), with a 3 dB per zone reduction to the rear. Delay towers maintain level rather than increasing it, filling in the natural SPL drop with distance.

Most festival sites have noise conditions attached to their entertainment license. These typically specify maximum levels at the nearest residential boundary, measured as LAeq over 15 minutes or 1 hour. Common limits are 65-75 dB LAeq daytime and 55-65 dB LAeq nighttime.

Use SonaVyx noise monitors at 2-3 boundary positions, running continuously throughout the event. Set threshold alerts 5 dB below the limit to allow time for the FOH engineer to reduce levels. Low-frequency energy (below 100 Hz) travels the farthest and is the most common cause of boundary complaints.

Multi-stage festivals must manage sound bleed between stages. The primary strategy is stage orientation: face stages away from each other so the loudest coverage area of each stage points away from adjacent stages. Cardioid subwoofer arrays (end-fire or gradient configurations) reduce rear radiation by 10-20 dB compared to omnidirectional sub arrays.

Scheduling helps: alternate high-energy and acoustic acts on adjacent stages so that a loud act on Stage A coincides with a quiet act on Stage B. Measure SPL at the midpoint between stages to verify that bleed is at least 10 dB below the active stage level.

Tune each stage system independently before the festival opens. Measure the transfer function at FOH and at 2-3 positions across the audience area. Set delay speakers to align with the main system at each delay tower position. Verify subwoofer integration at FOH and at the transition zone between main and delay coverage.

During the event, use SonaVyx SPL monitoring at FOH and at boundary positions. Track LAeq over 15-minute periods and compare against targets. If boundary levels approach limits, reduce bass level first (the most effective single adjustment for reducing propagation distance) before reducing overall level.