When the wind howls, what exactly is making the noise?
鈥� When the wind blows over, through or round an object, it can produce whispers, whistles or howls, depending on the shape of the object and the wind speed. The interaction creates turbulence in the air in the form of eddies, or vortices. As a vortex forms, there is a change in air pressure within it and this propagates a pressure wave. A series of vortices, produced at a certain frequency, will make a sound of the same frequency. As the wind speed rises, so does the rate of vortex formation and, hence, the pitch of the sound.
鈥淎eolian harps are musical instruments designed to be played by wind as it blows through their strings鈥�
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As wind blows through trees, it can produce the white noise of a waterfall because of the different frequencies formed at twigs, branches, boughs and trunks, which all have different diameters and textures.
If the wind blows past something like a wire fence, and the frequency of the vortex formation matches the resonant frequency of the wire, the wire will vibrate so that it sings, adding to the wind鈥檚 harmonies. Aeolian harps rely on this effect. They are musical instruments that produce sounds as the wind blows through their strings; they are named for Aeolus, the mythological keeper of winds.
David Muir, Edinburgh, UK
鈥� A neighbour who lived at the top of a hilly and windy estate in Yorkshire always complained about how noisy the wind was in his house. It whistled, howled and moaned around the property. While in his living room one day, I realised that the wind noise was louder when I was standing by his front window. I then noticed that someone at some time had drilled a hole through the bottom of his window frame in order to pass a TV aerial cable through. The cable had since been removed, leaving the open hole. I put my thumb over the hole and the wind noise instantly stopped. It had been acting like the mouth hole in a flute or a piccolo. We plugged the hole and that eliminated all the wind noise.
In summary, wind noise results from some small feature of a building that generates the vibrations of the air which then causes the sound.
William Poole, By email, no address supplied
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