Definitions, Terms, Units and Parameters

W

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W : under Watt

Waterfall

: a 3-D plot displaying the amplitude of spectral components as a function of both time and frequency. The frequency spectrum is displayed as a curve for each specified time instant. Several such curves, for different time instants, are displayed simultaneously.

Watt : W

: the unit of power.

The rate at which work is done, or (equivalently) the rate at which energy is expended. 1 watt is the power which in one second gives rise to energy of 1 joule.

1 watt = 1 J/s = 1 N·m/s : base unit m² kg s^-3

1 watt is equivalent to 1.341 x 10^-3 horsepower

A watt is also the power dissipated by a current of 1 ampere flowing across a potential difference of 1 volt.

Watt per square meter : W/m²

: a common metric unit of heat, flux, density, irradiance, base unit: kg s^-3

Watt second : W·s

: a common metric unit of work or energy, representing the energy delivered at a rate of 1 watt for a period of 1 second.

1 watt second = 1 J = 1 N·m

Waveform

: the waveform is the shape of a time domain signal as seen on an oscilloscope screen. It is a visual representation or graph of the instantaneous value of the signal plotted against time. Inspection of the waveform can sometimes reveal information about the signal that the spectrum of the signal does not show. For instance a sharp spike or impulse and a randomly varying continuous signal can have spectra that look almost identical, while their waveforms are completely different. In machine vibration, spikes are usually caused by mechanical impacting, while random noise can be caused by the advanced stages of bearing degradation

Wavelength : Λ

: for a sound wave is 345 m/s (speed of sound) divided by the frequency - the unit is metres. Wavelength is also defined as the distance between repeating units of a sound wave. 20 Hz = 17 m and 20 kHz = 17 mm.

The frequency f, wavelength λ and wave velocity v are related by the formulae λ = v/f

Wave Velocity

: the velocity of a wave is equal to the product of its wavelength and frequency.

Weber : Wb

: is the SI unit of magnetic flux, volt-seconds, causing the electromotive force of one volt in a circuit of one turn when generated or removed in 1 second.

Weekly Personal Noise Exposure : LEP,w

: a measure of the total noise received by an employee during a working week.

Similar to the Daily Personal Noise Exposure but calculated for a 40-hour week (five 8-hour days) instead of an 8-hour day.

Weighted Sound Pressure Level

is the Frequency Weighted and exponential Time Weighted - Sound Pressure Level.

Weighted Sound Reduction Index : RW
Weighted Standardized Impact Sound Pressure Level : LnT,w
Weighted Standardized Impact Sound Pressure Level : L'nT,w
Weighted Standardized Level Difference : DnT,w

Weighting Networks

: an electronic filter in a sound level meter or a vibration meter that correlates the objective meter measurement to the human response.

For example the frequency response of the human ear, in which case the A-weighting network is most commonly used with regard to noise control issues, regulations and environmental standards.

Similarly hand arm and whole body measurements are frequency dependent. There are a range of human vibration networks or filters because measurements are made in 3-axis and the weightings for whole body measurements, seated, standing or lying down are different from the hand arm filters see the list below.

Weighting Network : Bb

: for measuring whole body vibration in fixed-guide transport systems in seated or recumbent positions.

Weighting Network : Bc

: for measuring horizontal whole body vibration in the X direction, perpendicular to the spinal column, at the seat back.

Weighting Network : Bd

: for measuring horizontal whole body vibration in the X and Y directions, at right angles to the spinal column, in seated, standing or recumbent positions.

Weighting Network : Be

: for measuring rotational whole body vibration in 3-axis.

Weighting Network : Bg

: for evaluation of whole body vibration in the Z direction, with regard to hand control and visibility.

Weighting Network : Bh

: for measuring hand arm vibration in the X / Y / Z axis.

Weighting Network : Bj

: for measuring vibration acting on the head of a recumbent person in the vertical direction, perpendicular to the lying surface.

Weighting Network : Bk

: for measuring whole body vibrations in the direction of the spinal column in seated and standing positions, for measurements in the vertical direction, perpendicular to the lying surface in recumbent position and for measurements in the X / Y / Z axis acting on the feet in seated position.

Weighting Network : Bm

: for measuring whole body vibrations in buildings in the X / Y / Z axis.

Weighting Window

: Fast Fourier Transform theory tells us that time and frequency are simply two alternative ways of observing a signal. By changing the nature of a signal in the time domain, we implicitly change the nature of the spectrum in the frequency domain. This is exactly what we do when we apply a weighting function or time window.

White Finger

: disorder of the hands caused by using hand-held tools, such as chain saws and jack hammers. Results in reduction of the hand's ability to feel or to regulate its temperature. May also result in numbness and excessive sensitivity to low temperatures. Called Raynaud's disease.

White Noise

: sound containing all audible frequencies with equal intensity - see also pink noise.

Other Noise Terms.

Whole Body Vibration

: our bodies are exposed to vibration at work from many machines, such as construction machinery (bulldozers, tow motors, forklifts and cranes), heavy equipment (grinders, jack hammers), and power hand tools. Vibration has been proven to result in disorders of both the hand and arm, the neck, and the back.

See also The Control of Vibration at Work Regulations and Vibration Dose Value - VDV .

Whole-body vibration is defined by HSE as mechanical vibration which is transmitted into the body, when seated or standing, through the supporting surface, during a work activity. See also the daily exposure levels

Whole Body Weightings

Wideband Noise

also called broadband noise, whose energy is distributed over a wide section of the audible range as opposed to narrow band noise. White noise has equal power per unit bandwidth over a specified frequency range. Pink noise has equal power in constant percentage bandwidths (for example, octave bands) over a specified frequency range.

Other Noise Terms.

Windowing

: a technique used to reduce spectral leakage by multiplying the time-domain waveform by a window function. The process of windowing reduces the amplitudes of discontinuities at the edges of a waveform, thereby reducing spectral leakage.

Windscreens

: the 'foam' windscreens extensively used with sound level meters present some interesting problems. They reduce the wind noise by perhaps 15 dB or more on a good day, so in windy conditions how do you know you are measuring the noise source or the wind or a combination of the two? **

Some guidance is given in ISO 1996 (community noise survey noise standard) which recommends you measure downwind at wind speeds of between 1 and 5 m/s. This can result in wind 'generated' noise levels of around 30dB (A) with the windscreen on.

** a practical solution is to listen to the AC output of the sound level meter using earphones, or the audio recording feature included in some sound level meters like the B&K 2250

Work

: = force x distance = energy and is defined as the amount of energy transferred by a force. Like energy it is a scalar quantity with SI unit of both work and energy is the joule.

WBV : Whole Body Vibration

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