As spring and summer approaches we’re expecting warmer, longer days and with plenty of time to soak up some Vitamin D. But, the changing weather affects sound in terms of its sound output and traveling distance. There are different pressures, temperatures and moisture levels in the air around us that all contribute to how sounds travel (in terms of their direction and speed), and how loudly they are transmitted.
On most of KAMA Industries’ specification sheets, the sound distance that has been mentioned is calculated in still-air conditions. When it comes to the actual distance it travels, the variations can be significant when factors like wind, humidity and temperature are taken into account.
Did You Know?
- Sound can’t travel through a vacuum.
- The loudest natural sound ever produced was by the Krakatoa volcano in 1883.
- Sound travels about four times faster through water than through air.
- Sound travels at about 1234 km/hour.
- The loudest animal on earth is a sperm whale (making sounds of around 230 dB).
The Effect of Temperature on Sound
In simple terms, sounds move slower in cool air and faster in warm air. This means that slower-moving sound can be carried over longer distances. This is because air molecules tend to move around more in warmer conditions.
The atmosphere is made up of different layers of air, which are at different temperatures. So, as sounds move through the different temperatures, they will refract (or bend) because they are changing speed. In the summer daytime in South Africa, it is usually warm to hot closer to the earth’s surface. This bends the light upwards and away from the earth, which means away from our ears too. But, if the earth’s surface is at a lower temperature than the air a little higher up, the sound will be bent back towards the earth and us. So, sounds tend to be louder and carry further when the earth is cooler.
During the afternoon thunderstorms so typical of the Lowveld, the earth is very hot. So, even if the storm is only a little distance away from you, you’re not likely to hear much until you’re right in the thick of it. At night, though, thunder and lightning can be heard from far away, because of the cooler air refracting the sound back to earth.
The weather affects sound in another way. Temperature has a significant effect on the speed at which sound travels. For example; when the outside temperature is at 45° C, sound will travel at about 358 meters per second. In 21° C, that drops to about 343.6 meters per second. At -1° C, sound will only be travelling at about 330.4 meters per second.
The Effect of Humidity on Sound
Humidity refers to the amount of water vapour in the air. It is important to know that water vapour is lighter than air (air is made up of nitrogen and oxygen molecules, which are heavier than the vapour molecules). Also, air absorbs energy from the sound travelling through it, which weakens the sound. Dry air absorbs more sound than moist air. So, sound travelling through dry air will be weakened, while sound travelling through moist air (or in a higher humidity) will carry a little further.
The Effect of Wind on Sound
To put it simply, wind bends sound waves. So, more than speeding it up or slowing it down, dulling or amplifying it; the effect that the wind has on sound is one of distortion. In areas that get a lot of wind, the sounds produced by a siren can be dulled or even completely indistinct.
The wind that is closer to the earth’s surface moves slower than the wind that happens at higher altitudes. This causes sound waves to bend downwards, towards the slower wind. So, alarms and sirens that are upwind of people will be heard; but one that is downwind will be indistinct. The stronger the wind, the more dramatic the effect. This is just another way that weather affects sound.
What Does This Mean for You?
Deciding on the type, volume and placement of your audible warning system depends quite heavily on the prevailing weather conditions. If your factory, mine, warehouse, or other work area is located at high altitudes that experience a lot of wind, in valleys where the cold air settles, in particularly sweltering places, or those with high humidity; these factors will all play a role in how well your outdoor warning system conveys its important message.
In extreme conditions, it may even be necessary to add a visual system (flashing lights or a beacon) that will complement the audible system. Then, even when the sound is dulled or distorted, employees are able to benefit from the visual system.
How can KAMA Industries Help?
We understand how weather affects warning systems, and we supply audible and visual warning devices made for all conditions. For advice and a workable solution to your sound problem, contact us today on +27 11 472 3980 or e-mail us on info@kama.co.za.
