## What is Sound and Interesting Facts About Sound

In physics, sound is a wave of pressure. It occurs in a medium, which can be a solid, liquid or gas. Sound cannot travel through a vacuum, such as in space. The wave of pressure reaches our ears and causes the ear drum to vibrate, which then goes through a complex process to ultimately be perceived as audible sound.

There are several characteristics of sound waves that can be measured and help define the sound. A sound wave can be visualized as a repeating sinusoidal wave (see below), and can be described by these properties – frequency and wavelength, amplitude, and speed.

• Frequency is the number of cycles in 1 second, and is measured in Hertz (Hz)
• Wavelength is the distance over which 1 cycle occurs, and for audible sound is  between 17 m and 17 mm long
• Amplitude is the measure of its change over a single period, and normally a measure of sound loudness
• Speed is the distance traveled per unit time

The speed of sound in air can be found using the equation:  a = Sqrt (γ•R•T)

where for air:
γ = ratio of specific heats = 1.4,
R = gas constant = 286 m²/s²/K
T = absolute temperature in °K (273.15 + °C)

At room temperature, 22°C (71.6°F), the speed of sound is 343.8 m/s (760 mph)

• Sounds generally travels faster in solids and liquids than in gases.
• You can estimate the distance from a lightning strike by counting the seconds that pass between seeing the lightning flash and hearing the thunder.  Take this duration an divide by 5 to get the distance away, in miles.
• Humans normally hear sound frequencies between 20 Hz and 20,000 Hz.
• Sound waves above 20,000 Hz are known as ultrasound, and sound waves below 20 Hz are known as infrasound.
• Sound travel through water close to 4 times faster then through air.
• The sound of a cracking whip occurs because the speed of the tip has exceeded the speed of sound.

Sound that is too loud can be a problem. The Occupational Safety and Health Administration (OSHA) has set limits on the noise exposure that an employee can be subjected. Exceeding these values can cause permanent damage to your ears and cause noise induced hearing loss. So, knowing and reducing the sound levels within a manufacturing operation is important.

EXAIR has many products that can help reduce the sound levels in your processes.  With products such Air Knives, Air Wipes, Air Amplifiers, Air Nozzles and Jets, and Safety Air Guns, strong, quiet and efficient blowoff, drying, and cooling can be performed.

If you have questions about sound and keeping your sound levels in check or any of the 15 different EXAIR Intelligent Compressed Air® Product lines, feel free to contact EXAIR and myself or any of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer
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