Why delay speakers need delay
In large rooms and outdoor events, speakers placed partway into the audience ("delay towers", under-balcony and side fills) keep the sound loud and clear at the back. But sound from the main speakers takes time to travel – about 3 ms per meter. Without electronic delay, listeners near a fill speaker hear it first and the main system a moment later, creating a smeared double sound or a distinct echo. Delaying the fill speaker's signal lines the two up.
Delay (ms) = distance (m) ÷ speed of sound (m/s) × 1000 · speed ≈ 331.3 + 0.606 × °C
The Haas effect
When two similar sounds arrive within about 5 – 30 ms of each other, we hear one sound coming from the direction of the first arrival. By adding 5 – 15 ms beyond pure alignment, the main stage sound arrives slightly first, so the audience still "hears" the performers on stage while the delay speaker reinforces level and intelligibility.
Quick reference (20 °C)
| Distance | Delay | With +10 ms |
|---|
| 5 m (16 ft) | 14.6 ms | 24.6 ms |
| 10 m (33 ft) | 29.1 ms | 39.1 ms |
| 20 m (66 ft) | 58.3 ms | 68.3 ms |
| 30 m (98 ft) | 87.4 ms | 97.4 ms |
| 50 m (164 ft) | 145.7 ms | 155.7 ms |
Measuring the distance
The relevant distance is the difference in path length to the listeners the fill speaker serves: from the main speaker to those listeners minus from the fill speaker to the same listeners. For speakers in a line along the audience, that's roughly the distance between the main and delay positions. For front fills, measure to the first rows and align to the main PA or to the performers' voices.
Other uses
- Subwoofers and mains: align subs placed away from the tops.
- Stage backline: align the PA to loud guitar amps or drums so the sound comes together.
- Distributed ceiling systems: stagger delays along long halls and churches.
- Video screens: keep audio in sync with lip movement on large screens.
Frequently asked questions
How do you calculate speaker delay?
Divide the distance in meters by the speed of sound (about 343 m/s at 20 °C) and multiply by 1,000 for milliseconds – roughly 2.9 ms per meter or 0.9 ms per foot.
What is the Haas effect?
When two similar sounds arrive within about 5 – 30 ms, we perceive them as one sound coming from the first arrival's direction.
How much delay for a speaker 20 meters away?
About 58 ms at 20 °C, plus a 5 – 15 ms precedence offset.
Does temperature affect speaker delay?
Yes. Sound travels faster in warm air – about 0.6 m/s faster per °C.
How many feet does sound travel in a millisecond?
About 1.13 ft (0.343 m) at 20 °C.
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