Help Topics - W

Wave

A disturbance that travels through a medium such as air by virtue of the elastic properties of that medium.

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Wavelength

When considering periodic waves (such as the passage of sound in air) it is the distance between similar points on any two successive wave fronts.

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Wavelength of sound

The wavelength of a sound is inversely proportional to the frequency of that sound such that the lower the frequency, the longer the wavelength of that sound will be. The wavelength and the frequency of a noise are related by the speed of sound in air. For sound waves in air the typical wavelength of a 1 kHz tone is 34.4 cm (about 13.5 in). A low pitch sound such as the frequency of the electrical transmission system at 60 Hz the equivalent wavelength is 225 ft (5.73 m). All figures are based on standard temperature and pressure. For light the wavelengths are usually expressed in nanometers (nm or 10^-9m).

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WBGT

WBGT(indoor) = 0.7 tnw + 0.3 tg

WBGT (outdoor) = 0.7 tnw + 0.2 tg + 0.1 ta

The wet bulb globe temperature index is a means of specifying a measurable quantity to assess the risk of an operator suffering from heat stroke or other symptoms when working in hot areas. It is an empirical index based upon the relationship between the three different temperatures recorded by thermometers that measure the temperatures of the dry air, the globe and the natural wet bulb in the area where people are working. Corrections are applied depending upon the clothing and work rates to arrive at a safe WBGT temperature for indoors and outdoors.

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Weighting

An internationally prescribed frequency filter shape provided in sound measuring devices such as sound level meters to try and characterize the overall effect of certain sounds on a typical listener.

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Wet bulb thermometer

The temperature reported by a thermometer that has a wetted wick around it to measure the naturally aspirated temperature for WBGT measurements.

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White noise

Sound or noise whose energy is uniformly distributed over a wide range of frequencies such that there is constant energy per Hertz. When measured with an octave or third octave band filter set the spectrum of a white noise source will be seen to drop off at 3 dB per octave as the frequency increases.

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Wind chill

The additional cooling effect of wind that makes the temperature feel lower than that actually measured by a thermometer in still air. The temperature is still the same as in still air but it just feels colder because the body's heat is lost more quickly.

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Windscreen

A foam ball fitted over the microphone of a sound level meter to reduce the effects of wind induced noise on the readings being carried out. Windscreens are often manufactured from open cell design foams to allow free passage to the sounds of interest without unduly affecting the frequency response of the system beyond acceptable limits. Foam windscreens should always be used when performing outdoor measurements but will not be effective if allowed to become waterlogged or when used in high wind speeds in excess about 30 f/s (or 10 m/s, ~ 20 mph).

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