What might be the prevailing noise at a concert? (in the terms of wind).

We had a discussion recently with a client about our role at open-air concerts and how and our role when it comes to monitoring concert noise. We told her how it was our job to ensure that noise levels from the concert are kept to within a designated noise limit at the nearest noise sensitive property by means monitoring the noise levels and consulting with the touring sound engineer during the show. She jokingly said the following in response:

“ Well, obviously you weren’t doing your job properly! I live near Terenure and I could clearly hear Ed Sheeran playing in Phoenix Park last year. That’s miles away, on the north-side! The music would have needed to be blasting out of the speakers in order to reach my back garden, are people deaf? How come I can hear the sound from a concert when I’m on the other side of the city?”

Explanation:

No doubt, we believed her. These types of remarks are common; many people in south Dublin will hear the din of Longitude festival held at Marley Park every year, whilst residences on the north-side might catch a few songs from a Croke Park gig. What seems to strike people is the sheer distance between the venue and their home, and how sound can travel so far and be so clear, such that the person can make out every work sung by the artist. There are many variables that will influence how far sound will travel through air, here I will try to explain the basic science behind this phenomenon.

Sound propagation, the process by which sound travels from point A to point B, can be subject to interference that can either enhance the sound or detract from it. This interference can come from barriers between the two points, or interference/mixing with other sounds. However, the one we are interested in here (under unobstructed free-field conditions) is how meteorological conditions affect how this sound travels.

WIND’S EFFECT ON NOISE TRAVELLING:

Wind causes sound waves to bend (refraction) in the direction of the prevailing wind . Wind closer to the ground moves slower than wind at high altitudes. The difference in velocity creates a wind gradient, causing a sound traveling downwind to bend downwards, sort of like a golf-ball in flight. The prevailing wind will essentially carry sound waves further than they would have travelled without the wind; the significance of this effect depends upon the wind speed. Conversely, is the sound source is traveling against the wind, the sound will bend upwards with reduced propagation/ See the example of the car below.

Explanation: