A Filter

A Network

A-weighting

Absorption

Absorption Coefficient

Absorption Loss

see also DC Coupling.

The SI units are m/s^{2} or if using Imperial units then 'g' = 9.80665 m/s^{2} = 386.089 in/s^{2}

Displacement = v/ω

So at 159 Hz an acceleration of 10 m/s

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

If 1 N = 1 Kg·m/s^{2} it follows that m/s^{2} acceleration also equals N/kg Newtons per kilogram.

**Amax** is the maximum RMS Acceleration.

**Amp** is the maximum Peak Acceleration.

**aw** is time-averaged, frequency-weighted, single-axis vibration acceleration.

see also Angular Acceleration and Particle Acceleration, used in acoustic wave theory.

**The human response to vibration covers a wide range from a few
μm/s ^{2} to tens of metres per second squared. The dB scale is a useful way to represent the immense range using a manageable set of numbers.**

♦ Note 1: unless otherwise specified, the reference acceleration is 1 μm/s2.

♦ Note 2: unless otherwise specified, the accelerations are understood to be expressed in root-mean-square values.

An increase or decrease in acceleration of 20 dB = a factor of 10

An increase or decrease in acceleration of 40 dB = a factor of 100

An increase or decrease in acceleration of 60 dB = a factor of 1000 etc.

* see also the table of other Standard Reference Levels

To calculate the equivalent value for other periods use the formulae Aeq8 = a √T/8 where T = hours

Aeq4 and Aeq16 are also used in some vibration exposure applications.

see also :

Hand Arm Vibration

Vibration at Work Regulations

Vibration Dose Value

Whole Body Vibration

Za = p/Q : the SI Units are Pa·s/m^{5} (MKS units: acoustic ohms)

Zo = ρc : the SI units are N·s/m^{3}.

where R is the resistive part, and X is the reactive part of the impedance The resistive part represents the various loss mechanisms an acoustic wave experiences such as random thermal motion.

For the case of propagation through a duct, wall vibrations and viscous forces at the air/wall interface (boundary layer) can also have a significant effect, especially at high frequencies for the latter. For resistive effects, energy is removed from the wave and converted into other forms. This energy is said to be 'lost from the system'.

z = p/v : the SI units are Pa·s/m^{3} or rayls in MKS units.

The Real part of the acoustic impedance is termed **Acoustic Resistance**.

The Imaginary part of the acoustic impedance is termed **Acoustic Reactance**.

see Acoustic Impedance above.

more details under Sound Pressure

Active Intensity

Active Sound Field

**Admittance** under Acoustic Admittance

**ADPCM** : Adaptive Pulse Code Modulation

**Aeq : **Acceleration Equivalent Value - Aeq4, Aeq8, Aeq16

Age Related Threshold Shift : ARTS

**AI** : Articulation Index

**Airborne Sound Insulation Index : Ia''** former name for - Weighted Apparent Sound Reduction Index : R'w

**Because of their importance we have prepared more details Measurement Microphones**

Anti-aliasing filter

Nyquist Frequency

Background Noise

Residual Noise

Specific Noise

For a Damping Ratio = 0 (no damping) the amplification factor is infinite, for = 1 (critically damped) there is no amplification.

Angle of Incidence

Angle of Reflection

Units | Values | |||||||
---|---|---|---|---|---|---|---|---|

Degrees | 0° | 30° | 45° | 60° | 90° | 180° | 270° | 360° |

Radians | 0 | π/6 | π4 | π/3 | π/2 | π | 3 π/2 | 2π |

Grads | 0^{g } | 100^{g}/3 | 50^{g} | 200^{g}/3 | 100^{g} | 200^{g} | 300^{g} | 400^{g} |

Units : Radians per second squared, rads/s^{2}

θ = s/r = length of arc divided by the radius in Radians

To convert a Frequency in hertz to an angular frequency multiply by 2·π

For an oscillation with Period T, the angular frequency ω = 2·π / T

Units : newton metre seconds (N·m·s)

Units : radians per second, rads/s

see also Nyquist Frequency.

♦ Note : the appropriate modifier should be used to signify the other types; e.g. Particle Velocity Antinode or Sound Pressure Antinode

Apparent Sound Insulation Index : R'

Weighted Apparent Sound Reduction Index : R'w

The derived SI unit is the square metre, symbol : m^{2} : 1 m^{2} = 1 m by 1 m or 2 m by 0.5 m, etc.

25 mm by 25 mm = 0.025 m by 0.025 m = 0.000625 m^{2}

see also Cross Section Area

Articulation Index : AI

Articulation Intelligibility

**ARTS : **Age Related Threshold Shift

see also Sound Absorption

♦ Note : the unit is the Neper per metre.

a) acoustic oscillation of such character as to be capable of exciting a sensation of hearing

b) sensation of hearing excited by an acoustic oscillation or vibration

see also Critical Bands and Threshold of Hearing.

Average Sound Level

Average Speech Power

Ensemble Averaging

Exponential Averaging

Linear Averaging

RMS Averaging

Spatial Averaging

Spectrum Averaging

Time Domain Averaging

Time Weightings