# Acoustic Glossary

## V : Sound and Vibration Terms, Definitions, Units, Measurements ...

VDV • Vibration Dose Value

Vector Quantities have both magnitude and direction, for example displacement, velocity and acceleration are vector quantities. As opposed to scalar quantities like length, area, volume, pressure and power, which have magnitude but no direction.

Vectors can only be added, subtracted or multiplied using mathematical procedures that take account of the co-ordinates.

Vector spaces are applied throughout mathematics, science and engineering. They are the linear-algebraic notion to deal with systems of linear equations; offer a framework for Fourier expansion or provide an environment that can be used for solution techniques for partial differential equations.

Velocity (v) the rate of change of position and is a vector quantity as both speed and direction are required to define it, the SI units are m/s (metres per second).
v = u + at   where v = velocity, u = start velocity, a = acceleration in m/s2 and t = time.
In the field of vibration acceleration a, velocity v, displacement and angular frequency ω = 2·π·f , are related.
Velocity v = a/ω
Displacement s = v/ω
It follows that 10 m/s2 = 0.01 m/s = 10 μm at 159 Hz.

This works for all frequencies, we just chose 159 Hz to keep the numbers simple. We also have a vibration nomogram for downloading.

Velocity Level (Lv) also known as vibratory velocity level = 20 lg(v/vo) dB re 1 nm/s
Velocity reference level : vo = 1 nm/s ≡ 0 dB (defined in ISO 1683) *

An increase or decrease in velocity of 20 dB = a factor of 10
40 dB = a factor of 100
60 dB = a factor of 1000, etc.

* ISO 1683 also states 'in connection with structure-borne sound, a reference value of 50 nm/s is also in use. In this event, the vibratory velocity level takes values close to the associated sound pressure and sound intensity levels'

See also • angular velocity. • particle velocity, used in acoustic wave theory • peak particle velocitystandard reference levels table • volume velocity and the IEC definition of level

Velocity of Sound is usually taken to mean the speed of sound. Not be confused with sound particle velocity, which is the velocity of the individual particles of the medium the sound wave is passing through. To add to the confusion the unit v is often included.

Vibration is the movement of particles in an elastic medium about an equilibrium position. The movement may be periodic such as the motion of a pendulum or random.

Vibration is commonly expressed in terms of acceleration, velocity, displacement and frequency which are related.

Vibration Acceleration Level

Vibration at Work Regulations, came into force in July 2005 to protect workers from risks to their health from vibration, based on hand arm and whole body vibration exposure action and limiting values.

Vibration Dose Value

Vibration Exposure Action Value
Vibration Exposure Limit Value

Vibration Parameters
Acceleration
Velocity
Displacement

Vibration Reference Levels

Vibration Regulations, see Vibration at Work Regulations

Vibration Velocity under velocity

Vibration Weighting Networks

Vibration White Finger

Vibratory Acceleration Level
Vibratory Velocity Level

Viscous Damping Definition IEC 801-24-22, damping that occurs when a particle in an oscillating system is resisted by a force that has a magnitude proportional to the magnitude of the velocity of the particle and direction opposite to the direction of the particle

Voice Simulator Definition IEC 801-28-07, complex sound, usually emitted by an artificial mouth whose spectrum corresponds to that of the average human voice. Also known as an artificial voice

Volt (V), the derived SI unit of electric potential; the potential difference between two points on a conductor carrying a current of 1 ampere, when the power dissipated between these points is 1 watt

Voltage Level (LV) is the voltage expressed in decibels, relative to 1 volt rms, regardless of impedance.
LV = 20 lg (V/Vo) dBV

The reference voltage : Vo = 1 volt ≡ 0 dB

Volume (V), a scalar quantity is the amount of space that an object or substance occupies, the SI unit is the metre-cubed (m3).

Volumetric Flow Rate (Q) is the volume of fluid which passes through a given surface per unit time.
Q = v·A, where v = velocity, A = area/surface and the SI units are m3/s.

Volumetric flow rate is also known as the volume flow rate, rate of fluid flow and volume velocity

Volumetric Flux (q) is the volumetric flow rate across a unit area. SI units : m3·s-1·m-2

Volumetric Power Density, volume based power density - watt/m3

Volume Velocity Definition IEC 801-21-31, integral, over a vibration surface, of the product of the component of particle velocity normal to the surface and the differential surface area. Also known as sound volume velocity, volumetric flow rate and volume flow rate 