Wind effects on the sound of bells

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The sound of bells are created by a series of constant harmonic partials. If you notice that your stationary bell seems to vary in pitch outside, but it sounds stable through the indoor monitors you may be experiencing environmental distortion. If you hear a warbling sound inside, try turning off fans.

Wind and Sound

Wind is the motion of air. Meteorologically, it is the movement of air mass from high to low pressure areas.

Wind effects are divided into two classes: velocity effects and gradient effects. Wind velocity - specifically in the form of a cross wind - can shift the direction of the sound, making it appear to come from a different location. Wind gradient effects occur when one air layer is moving at a different speed than an adjacent layer; usually one layer is above the other. Such a gradient might be encountered when the audience is shielded from the wind by a barrier (such as a group of trees or a wall). The effect of this would cause the sound to be refracted upward and downward respectively. Now, having said all of this, the actual effect of wind is usually minimal due to the speed of wind versus the speed of sound - sound being drastically faster.

Certainly, the height of the bell tower and the speed of wind would be deciding factors, but it usually take a pretty strong wind to have a significant effect. Of course, the effect will be cumulative, so the sonic changes will be proportional to how far you are from the bells or speakers. Further, the effect will usually be more pronounced at higher frequencies due to their small wavelengths - longer wavelength sounds aren't as easily effected by obstacles, wind or otherwise.

Sometimes wind can have the appearance of having a large effect on sound, but that is often due to temperature gradients that accompany wind.