Audio calculator
Speaker Delay Calculator
Sound travels roughly 343 meters per second (1,125 ft/s) at 20°C, which works out to about 2.9 milliseconds per meter or 0.9 milliseconds per foot. Enter the distance between your main PA and the delay speaker, and this calculator returns the delay time to set, corrected for air temperature.
Sound travels faster in warmer air, so outdoor delay times drift as temperature changes.
Formulas
Speed of sound
c = 331.3 + 0.606 × T- c:
- speed of sound in m/s
- T:
- air temperature in °C
Delay time
t = (d / c) × 1000- t:
- delay time in milliseconds
- d:
- distance in meters
How it works
When a delay tower or fill speaker reproduces the same program as the main PA, listeners near it hear two arrivals: one from the close speaker and one from the mains. If the close speaker is not delayed, its sound arrives first and the image pulls away from the stage, with comb filtering in the overlap zone.
Delaying the fill so its output lines up with the arrival from the mains restores a single coherent wavefront. The required delay is simply the extra distance the main PA’s sound has to travel, divided by the speed of sound.
Many engineers add 5–10 ms on top of the calculated time so the mains arrive slightly earlier at the listener. The precedence (Haas) effect then keeps the perceived image anchored on stage even though the fill is doing much of the acoustic work.
Worked example: Delay tower 30 m behind the main PA at 20°C
- 1.Speed of sound: c = 331.3 + 0.606 × 20 = 343.4 m/s.
- 2.Delay time: t = (30 / 343.4) × 1000 = 87.4 ms.
- 3.Optional precedence offset: 87.4 + 8 = 95.4 ms so the mains lead perceptually.
Set the delay tower to roughly 87 ms, or ~95 ms with a Haas offset.
Delay per unit distance at common temperatures
| Air temperature | Speed of sound | Delay per meter | Delay per foot |
|---|---|---|---|
| 0°C / 32°F | 331.3 m/s | 3.02 ms | 0.92 ms |
| 10°C / 50°F | 337.4 m/s | 2.96 ms | 0.90 ms |
| 20°C / 68°F | 343.4 m/s | 2.91 ms | 0.89 ms |
| 30°C / 86°F | 349.5 m/s | 2.86 ms | 0.87 ms |
| 40°C / 104°F | 355.5 m/s | 2.81 ms | 0.86 ms |
Field notes
- Laser distance meters read to the wrong point on an arrayed hang; measure to the array’s acoustic center, roughly the middle of the hang for a full-range array.
- For outdoor festivals, re-check delay times when the temperature swings more than ~5°C between soundcheck and showtime.
- Modern alignment tools (Smaart, M1, console delay wizards) measure arrival directly; use this calculator for the starting point and speed sanity checks.
Frequently asked questions
How many milliseconds of delay per foot?
About 0.89 ms per foot at 20°C (68°F). A common field approximation is 1 ms per foot, which overshoots by roughly 11%: fine for a quick sanity check, but calculate properly for delay towers.
How many milliseconds of delay per meter?
About 2.91 ms per meter at 20°C. At 0°C it rises to about 3.02 ms per meter because sound travels slower in cold air.
Does temperature really matter for delay times?
Yes. Between a 10°C soundcheck and a 30°C afternoon show, the speed of sound changes by about 3.5%. On a 100 m throw that is a shift of more than 10 ms, which is clearly audible as image smear near the delay line.
Should I measure the distance to the mains or to the stage?
Measure from the acoustic center of the main PA hang to the delay speaker. The mains are the reference arrival you are aligning to; the stage itself is not the source unless you are also aligning to backline spill.