How to Time-Align Delay Speakers at Outdoor Events

TL;DR

Delay speaker alignment is critical for intelligibility and imaging at outdoor events. Misaligned delays create comb filtering, echo, and confused localization. This guide covers measuring propagation delay, calculating delay compensation, and verifying alignment using transfer function phase and impulse response.

Why Delay Alignment Matters

Sound travels at approximately 343 m/s (1 ms per 0.343 m). A delay tower 30 meters from the main PA arrives 87 ms late. Without compensation, listeners between the main and delay hear both arrivals — creating comb filtering (periodic nulls every 1/delay Hz) and a perceived echo if the delay exceeds 30-50 ms.

Step-by-Step Procedure

Measure the physical distances. Use a laser rangefinder or tape measure to determine: (A) distance from main PA to the delay speaker alignment point, and (B) distance from the delay speaker to the same point. The alignment point is typically the first row of seats covered by the delay speaker.
Calculate the initial delay. Delay time = (Distance A - Distance B) / 343 × 1000 ms. If the main PA is 40 m away and the delay speaker is 5 m away, delay = (40 - 5) / 343 × 1000 = 102 ms. Add 5-10 ms extra to preserve the Haas effect (precedence effect ensures localization toward the main PA).
Set the calculated delay on the delay speaker's processor or DSP. This is your starting point — fine-tuning comes from measurement.
Open SonaVyx Transfer Function mode at /measure?mode=tf. Position the measurement microphone at the delay speaker alignment point.
Measure with main PA only. Mute the delay speakers. Play pink noise through the main PA and capture a transfer function trace. Store this trace (press S) as your reference.
Measure with delay speaker only. Mute the main PA. Unmute the delay speaker. Capture another trace. The delay finder in SonaVyx shows the propagation time from the impulse response.
Measure with both systems on. Unmute both. The combined transfer function should show a smooth magnitude response. Comb filtering (regular periodic dips) indicates a time alignment error. Adjust the delay in 0.5 ms increments until the comb filtering is minimized.
Verify phase alignment. In the combined measurement, check that the phase between 200 Hz and 2 kHz is smooth and does not show sudden wraps at the crossover region between main and delay coverage.
Account for temperature. Outdoor sound speed varies with temperature: c = 331.3 + 0.606 × T(°C). At 35°C, sound travels at 352.5 m/s (2.7% faster than the 20°C reference). For a 40 m path, this changes the arrival by 2.5 ms. Remeasure if temperature changes significantly during the event.

Common Mistakes

Using distance-only calculation. Wind, temperature gradients, and obstacles change the effective speed of sound. Always verify with measurement.
Forgetting the Haas offset. Setting exact time alignment causes the delay speaker to compete with the main PA for localization. Add 5-10 ms extra delay to keep the audience localized toward the stage.
Aligning at the wrong position. Align at the first row of the delay coverage zone, not the last. Listeners behind the alignment point hear the delay first (acceptable) while listeners in front hear the main first (also acceptable).
Not accounting for temperature drift. At a day-into-night event, temperature drops 10-15°C. This shifts arrival times by 5-10 ms over a 50 m path. Recheck alignment after sunset.

Tool Bridge

Open SonaVyx Transfer Function mode and use the delay finder to measure propagation times. The impulse response view shows arrival times for each speaker system.