Acoustic Glossary


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

VDV : Vibration Dose Value

Vector is a quantity having both magnitude and direction, for example acceleration, force and velocity.

As opposed to scalar quantities like density, mass and speed which have magnitude but no direction.

Vectors can only be added, subtracted or multiplied using mathematical procedures that take account of the co-ordinates. A vector is defined as an element of a vector space.

Vector space 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 metres per second, (m/s).

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.

See also : Particle Velocity and Volume Velocity

Velocity Level also known as Vibratory Velocity Level : Lv = 20 lg(v/vo) dB re 1 nm/s

The 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
a 40 dB = a factor of 100
a 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.

Should not be confused with sound particle velocity, which is the velocity of the individual particles. To add to the confusion the unit v is often included.

Vibration mechanical oscillations occur about an equilibrium point. The oscillations 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.

See also the table of dB Reference Levels and Vibration Dose

Vibration Acceleration Level : La

Vibration at Work Regulations The Control of Vibration at Work Regulations 2005 (the Vibration Regulations), came into force on 6 July 2005 and aim to protect workers from risks to health from vibration.

The Regulations introduce the Action and Limit Values for hand arm and whole body vibration.

For others details see the Government and/or HSE websites.

See also : Acceleration Equivalent Value : AeqHand Arm Vibration Syndrome : HAVSWhole Body Vibration : WBVCertified Vibration at Work Instrumentation

Vibration Dose Value : VDV

Vibration Parameters

Vibration Reference Levels

Vibration Regulations see Vibration at Work Regulations above

Vibration Velocity Level : Lv

Vibration Weighting Networks

Vibration White Finger : VWF

Vibratory Acceleration Level

Viscous Damping IEC Definition,

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 under 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 dB (1 V RMS) : voltage relative to 1 volt, regardless of impedance.

Lv = 20 lg (V/Vo) dBV
The Reference Voltage : Vo = 1 volt ≡ 0 dB

Volume : V the amount of space that an object or substance occupies, the SI unit is the cubic metre : 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 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 IEC Definition,

integral, over a vibration surface, of the product of the component of particle velocity normal to the surface and the differential surface area

VWF : Vibration White Finger : under Hand Arm Vibration


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