See also : Control of Vibration at Work Regulations • Action and Limit Values for Hand Arm and Whole Body Vibration

The Noise at Work Directive 2003/10/EC defines the following limit and action values:

LCpeak is the maximum value of the C-weighted, instantaneous noise pressure.

See also : Daily Personal Noise Exposure, LEP,d below

See also the **IEC Definition** of Level

If the Leq is measured over 8 hours then Leq and LEP,d and LEX,8h would all be the same.

The European Directive recommends LEX,8h is adopted from 2006 onward.

See also : Leq: equivalent continuous sound level

The term often refers to the attenuation of sound in a structure owing to the internal sound-dissipating properties of the structure or to the addition of sound-dissipative materials.

The action of frictional or dissipative forces on a dynamic system causing the system to lose energy and reduce the amplitude of movement.

Removal of echoes and reverberation by the use of sound absorbing material. See also Reverberation Time

**Day Noise Indicator** Lday

**Day-evening-night Noise Indicator** Lden

**Day-night Noise Indicator** Ldn

dBA, dBB, dBC, dBD, dB Flat, dB Linear and dBZ Frequency Weighting Filters

● Note 1 : the kind of level is indicated by use of a compound term such as sound power level or sound pressure level.

● Note 2 : the value of the reference quantity remains unchanged, whether the chosen quantity is Peak, the RMS, or otherwise.

● Note 3 : the base of the logarithm is indicated by use of a unit of level associated with that base.

dB SIL : Sound Intensity Level

dB SPL, dB(SPL), dBSPL and dBSPL in common use but not officially recognised

dB SWL : Sound Power Level

L in dB = 20 · lg (V/Vo)

See also : AC Coupling.

● Note 1 : the decibel is more often used than the bel as a unit of level.

● Note 2 : the decibel can be defined as a unit of level of a power-like quantity when the base of the logarithm is the tenth root of ten. Also, the decibel is the unit of level of a field quantity when the base of the logarithm is the 20th root of ten.

**decibel scale** a linear numbering scale used to define a
logarithmic amplitude scale, thereby compressing a wide range of amplitude values to a small set of numbers.

Vibration Levels | Sound Levels | |||

Acceleration : La | Velocity : Lv | Particle Velocity : Lv | Pressure : Lp | |

dB | m/s^{2} | m/s | m/s | Pa, N/m^{2} |

0 dB | 1 x 10^{-5} | 1 x 10^{-9} | 5 x 10^{-8} | 2 x 10^{-5} |

20 dB | 1 x 10^{-4} | 1 x 10^{-8} | 5 x 10^{-7} | 2 x 10^{-4} |

40 dB | 1 x 10^{-3} | 1 x 10^{-7} | 5 x 10^{-6} | 2 x 10^{-3} |

60 dB | 1 x 10^{-2} | 1 x 10^{-6} | 5 x 10^{-5} | 2 x 10^{-2} |

80 dB | 0.1 | 1 x 10^{-5} | 5 x 10^{-4} | 0.2 |

100 dB | 1.0 | 1 x 10^{-4} | 5 x 10^{-3} | 2.0 |

Table Notes :

0 dB is the reference level for each parameter.

The parameters above use the 20 Lg formulae for example 20 Log10 (P/Po) dB for Sound Pressure Levels.

Sound | Power Level, LW | Intensity Level, LI | Energy Density Level, LE |

dB | Watts | Watts/m^{2} | Joules/m^{3} |

0 dB | 1 x 10^{-12} | 1 x 10^{-12} | 1 x 10^{-12} |

20 dB | 1 x 10^{-10} | 1 x 10^{-10} | 1 x 10^{-10} |

40 dB | 1 x 10^{-8} | 1 x 10^{-8} | 1 x 10^{-8} |

Although in common use, the degree is not part of the International System of Units (SI) the derived unit is the Radian.

See also : Angles

SI units: kilogram per cubic metre, kg/m^{3}

At sea level and at 20 °C, air has a density of approximately 1.2 kg/m

At sea level and at 0 °C, air has a density of approximately 1.3 kg/m

See also : Stationary Signals. • Transients may also be deterministic.

DFT : Discrete Fourier Transform

Diffraction

Diffraction Factor

See also : Sampling.

Place the source on the ground next to a wall so the radiation is concentrated into a 1/4 of the sphere, then Q=4.

If the source is placed on the floor in a corner, the sound energy is further concentrated into 1/8th of a sphere so Q = 8.

See also : Tonal Assessment

Displacement : ξ = v/ω = a/ω^{2}, where v =
Velocity, a =
Acceleration and ω = 2·π·f = angular frequency.

Velocity v = a/ω

Displacement s = v/ω

So it follows that 10 m/s^{2} = 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 : Angular Displacement • Particle Acceleration • Particle Displacement used in acoustic wave theory • Particle Velocity • Standard Reference Levels table

**Distance** change in position of an object in metres -

See also : Displacement above.

● Note : Distortion may result from:

a) non-linear relation between input and output;

b) non-uniform transmission at different frequencies;

c) phase shift not proportional to frequency.

● Note : Divergence Loss exists, for example, for spherical waves emitted by a point source.

Dn : Normalized Level Difference

DnT : Standardized Level Difference

DnT,w : Weighted Standardized Field Level Difference

DnT,w + Ctr : Weighted Standardized Level Difference with Spectrum Adaption Term Ctr

**DOD : Department of Defence - USA**

**Dose related subjects**

DOHR

Dose - Noise

Dose%

Dose Badge

Dose per Hour

Dose - Vibration

Dosimeter

DSP : Digital Signal Processing

Dual Input Room Acoustics Calculator : DIRAC

Dw : Weighted Level Difference

1 dyne = 1 g·cm/s^{2} = 10^{-5} kg·m/s^{2} = 10 μN