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.
See also • sound power
See also • PCM and ADPCM.
See also • sound waves definition etc.,
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.
See also • Leq - equivalent continuous sound level.
So weight and mass are related, but not the same thing. An object with a mass of 1 kg would weigh about 9.8 newtons on earth, but 6 times less on the moon, due to gravity. In space an object still has mass but is weightless.In everyday use the term weight nearly always means mass. In science weight is the force due to gravity and the units are newtons.
Similarly hand-arm and whole-body vibration 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.
However levels measurements using sound analysers with 1/1 or 1/3 octave (constant percentage bandwidth) filters will increase by 3dB for each increasing frequency step. Pink noise on the other hand will produce constant levels across the spectrum.
Other noise descriptors • ambient noise • background noise • broadband noise • gaussian noise • narrowband noise • periodic • pink noise • pseudo random noise • random noise • residual noise • specific noise • wideband noise
Whole-body Vibration exposure assessment
The assessment of the level of exposure to vibration is based on the calculation of daily exposure A(8) expressed as equivalent continuous acceleration over an eight-hour period, calculated as the highest (rms) value, or the highest vibration dose value (VDV) of the frequency-weighted accelerations, determined on three orthogonal axes (1,4awx, 1,4awy, awz for a seated or standing worker) in accordance with Chapters 5, 6 and 7, Annex A and Annex B to ISO Standard 2631-1 (1997).
Other noise descriptors • ambient noise • background noise • broadband noise • gaussian noise • narrowband noise • periodic • pink noise • pseudo random noise • random noise • residual noise • specific noise • white noise
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