What can affect Sound Outdoors

How does Temperature, Humidity, and Wind affect Sound Outdoors?

Temperature – Yes, temperatures can affect sound outdoors. Sound can “slow down” as the air gets colder and “Speed up” when temperatures are hot. This is related to the difference in “density” between cold and hot air. Since cold air is denser than hot air – the sound will slow down in colder air and speed up as the air gets hotter. Although temperature affects sound waves, it is not as distinct as the effect that wind has on sound waves.

Humidity – Basically, sound waves will travel faster in high humidity. Why? Because humid air is not as dense as dry air. That said, the humidity effect on sound waves will only affect frequencies 2kHz and above.   

Wind –Different things can occur when the sound goes in the same direction as the wind, if the sound is going against the wind, or when the sound is caught in cross-winds. Wind can give the impression that sound is coming from different directions than it’s really coming from. During a strong cross-wind, if the listener faces a speaker, it could give the illusion that the sound is coming from the left or right. This is called “refraction” (which describes the “bending” of sound waves).

Although Temperature, Humidity, and Wind can potentially affect sound waves outdoors – The effect will be small and barely noticeable to the average listener. The biggest “threat” to live sound outdoors would actually be the factors of the “Environment” and “Surroundings” of the location of the sound system. 

 “Environment and Surroundings” – Basic Information

• Is the sound bouncing off the buildings?
• Is something covering or obstructing the front of the speaker? Such as a sign, drapes, a large light fixture, a prop, or even a flag or banner?
• Are there any reflective surfaces? Such as Glass, Plexiglass, Concrete, Wood, Metal walls, Steel structures, etc?
• Are there any “absorbent” materials in the environment? Such as Drapes, Acoustic Foam, Styrofoam?

These are things that an audio technician needs to be aware of when setting up a PA system outdoors. Finding a suitable location for a PA system is easy enough if you understand the Environment and Surrounding Area you are planning to install the system in.

Rain / Wind Storms

When setting up PA systems outdoors, you must have a rain plan. This means not waiting until it rains to figure out you could’ve used a few more Tarps to cover the equipment. PA equipment can cost a lot of money to replace, so why take any chances? For power, you should be using AC Extension Cables with GFCIs (Ground Fault Circuit Interrupters), and if possible, purchase speaker covers (or make your own using thick plastic). Our team ran out of speaker covers and made their own – cut out the plastic, formed it over the speaker, used duct tape (or Gaff tape) to hold the plastic in place, folded the plastic covers up, and stored them nearby. For Wind Storms, ensure all the equipment is “tied down” so it can’t blow over. Be prepared for rain and strong winds, and keep the equipment protected.