**R** : Sound Reduction Index - Laboratory Measurements

**R'** : Apparent Sound Reduction Index - Field Measurements

To convert radians to Degrees multiply the radians by 180/π : see also Angles

**Radian per second : rad/s** see angular velocity

Used for measurements in reflective room and chambers as opposed to the Free-field Microphones, used for measurements in more open spaces. The presence of the microphone should not to effect the measurement.

Because of their importance in acoustics we have a full page on Measurement Microphones

See also :
Free-field Microphones •
Pressure Microphones

**Pseudo Random Noise** electronically generated noise which may appear to lack any pattern, but does consist of pulses that repeat themselves periodically. The period is determined by the generator span and the number of generator lines.

Related Terms:
Broadband Noise •
Narrowband Noise •
Pink Noise •
White Noise

See also :
Constant Bandwidth •
Constant Percentage Bandwidths •
Octave Bands •
FFT- Fast Fourier Transform

Rapid Speech Transmission Index : RASTI

**RASTI** : Rapid Speech Transmission Index

Caution: Rayls may be in MKS and or CGS units, which are not the same.

**RC** : Room Criteria

See also : Acoustic Impedance

Reactive Intensity

Reactive Sound Field

Reactivity Index

**Reference Frequencies** under Preferred Frequencies

**Reference Levels** : expressed in SI units

Reference Particle Velocity : vo = 5 x 10^{-8} m/s ≡ 0 dB

Reference Sound Energy : Wo = 10^{-12} J ≡ 0 dB

Reference Sound Energy Density : wo = 1 pJ/m^{3} = 10^{-12} J/m^{3} ≡ 0 dB

Reference Sound Exposure : Eo = (20 μPa)^{2} s ≡ 0 dB

Reference Sound Intensity : Io = 1 pW/m^{2} = 10^{-12} W/m^{2} ≡ 0 dB

Reference Sound Power : Po = 1 pW = 10^{-12} W ≡ 0 dB

Reference Sound Pressure : po = 20 x 10^{-6} Pa ≡ 0 dB in air

Reference Sound Pressure : po = 1 x 10^{-6} Pa ≡ 0 dB in liquids and solids

Reference Vibratory Acceleration : ao = 1 μm/s^{2} ≡ 0 dB

Reference Vibratory Displacement : ξo = 1pm ≡ 0 dB

Reference Vibratory Force : Fo = 10^{-6} N ≡ 0 dB

Reference Vibratory Velocity : vo = 1 nm/s ≡ 0 dB

Reference Voltage : vo = 1 Volt ≡ 0 dB

Reflected Wave

Refraction
Refraction Loss

See also : Background Noise

See also : Acoustic Impedance

● Note : the quantity that is the measure of response should be indicated; for example, velocity resonance.

● Note : in case of possible confusion, the type of resonance must be indicated; for example, velocity resonance frequency.

Reverberant Field

Reverberant Sound Field

Reverberation is a significant parameter in Acoustics - so we have more details

See also : Early Decay Time • Schroeder • Backward Curve Integration

**RMS / Quadratic Mean** is the square root of the arithmetic mean of the squares of the numbers in a series

In acoustics the RMS value is also known as the Effective value.

The abbreviation RMS was formerly denoted as r.m.s. or rms, but these notations are now deprecated

See also : Ensemble Averaging• Exponential Averaging • Linear Averaging • Spatial Averaging • Spectrum Averaging • Time Domain Averaging

Room Absorption

Room Absorption Coefficient

The B&K 2250 Sound Analyser, measures RC values.

Root Mean Quad : RMQ

Root Mean Square : RMS

**rpm : **revolutions per minute

**RT** : Reverberation Time

**RT60** : Reverberation Time

**RTA** : Real Time Analyser

**Rw** : Weighted Sound Reduction Index

**R'w** : Weighted Apparent Sound Reduction Index