Sound Propagation Delay
Definition
Sound Propagation Delay
Sound propagation delay is the time required for an acoustic wave to travel from a source to a receiver through air. At 20°C, sound travels at approximately 343 m/s (1,125 ft/s), resulting in about 2.9 ms of delay per meter. Temperature, humidity, and altitude affect propagation speed. SonaVyx accounts for propagation delay in speaker alignment calculations and delay line settings.
Delay = distance / speed of sound; Speed ≈ 331.3 + (0.606 × T°C) m/s
How It Is Measured
Propagation delay is calculated from the distance between source and receiver using the speed of sound at the ambient temperature. SonaVyx measures the actual propagation delay by capturing the impulse response, which shows the arrival time of the direct sound. Comparing the measured arrival time to the calculated delay based on distance confirms the effective speed of sound in the measurement environment.
Practical Example
An outdoor festival main PA is 40 meters from a delay tower. At 30°C, the speed of sound is 349.5 m/s, giving a propagation delay of 114.4 ms. At soundcheck at 15°C, the speed drops to 340 m/s, and the delay becomes 117.6 ms. The 3.2 ms shift requires adjusting the delay tower timing to maintain alignment. SonaVyx automatically detects the arrival time difference and recommends the correction.
Temperature Effects
The speed of sound increases by approximately 0.6 m/s per degree Celsius. For a 40-meter throw, a 15°C temperature change (morning to afternoon) shifts the propagation time by about 3 ms — enough to cause audible comb filtering at the overlap with delay speakers. For precision-aligned systems, SonaVyx recommends re-measuring alignment when temperature changes more than 5°C from the initial calibration conditions.
Humidity and Altitude
Humid air is slightly less dense than dry air (water molecules are lighter than nitrogen and oxygen), so sound travels slightly faster in humid conditions — approximately 0.1% faster at 100% humidity compared to dry air. The effect is small enough to be ignored for most practical applications. Altitude reduces air density, increasing sound speed slightly, but the effect is dominated by the temperature decrease at higher altitudes.
Wind and Refraction
Wind adds or subtracts from the effective sound speed depending on direction. A 5 m/s headwind delays sound by approximately 1.5% (1.7 ms over 40 meters). Temperature gradients cause sound to refract — warmer air near the ground bends sound upward (temperature lapse), while temperature inversions bend sound downward, potentially increasing noise impact at distance. These effects are significant for outdoor events.
Try It Now
Measure propagation delay — free impulse response analysis