Gracey & Associates
Noise and Vibration
Glossary - R
GLOSSARY INDEX:
A B C
D E F
G H I
J K L
M N O
P Q R
S T U
V W X
Y Z
Radian : rad : a derived SI unit of angle measurement. One radian is the angle at the centre of a circle that cuts off an arc of length equal to the radius. Since the circumference equals 2 π times the radius, then one radian equals 360°/(2 π) or 180°/π, approximately 57.3°
To convert radians to degrees multiply the radians by 180/π
Radian per second : rad/s : angular velocity
Random Noise : random noise is a signal whose instantaneous value varies randomly with time. In the context of assessing hearing damage, any audible sound should be regarded as noise. Pink noise is random noise whose spectrum falls at 3 dB per octave: it is useful for use with sound analyzers with constant percentage bandwidths - see also white noise.
Random Vibration : a vibration whose instantaneous amplitude is not specified at any instant of time.
Rapid Speech Transmission Index : RASTI : is an objective way of measuring speech intelligibility. It is measured by placing a loudspeaker, which transmits sound from the location of the person speaking, and a microphone where the listeners are situated - see also speech transmission index.
RASTI : Rapid Speech Transmission Index.
Rayl : is the SI derived unit of acoustic impedance. 1 MKS rayl = 1 pascal-second per metre, Pa·s/m - 1 newton-second per cubic metre, N·s/m³ - named after Lord Rayleigh.
Raynaud's Syndrome : Hand-arm Vibration Syndrome
Reactive Intensity : the part of the sound field that does not contribute to the net flow of energy - see sound intensity.
Reactive Sound Field : a sound field in which the particle velocity is 90° out of phase with the pressure, a standing wave is an example of this type of field.
Real Time Analyzer : RTA : a device which uses a number of narrow bandwidth filters connected to a display to give a visual indication of the amplitude in each frequency band simultaneously or at the same time.
Real Time Frequency Analysis : measurement of octave or third octave band noise where all the filters are measured simultaneously, ensures no loss of data.
Real World +4 dB : in the real world there are factors that can reduce the effectiveness of hearing protectors: imperfect fitting and the condition of the protectors are two examples. To allow for this the HSE recommends the addition of 4 dB to the calculated level at the ear.
Rectangular Time Window : a time window that has a zero value outside the specified time record and unity within the record length. In the FFT analyzer, the rectangular window is actually no window at all. It is also called rectangular weighting, or uniform weighting, and is used when the signal to be analysed is a transient rather than a continuous signal - see also Hanning Window.
Reference Sound Pressure : a reference pressure of 20 μPa = 20 micro pascals. This reference pressure was chosen conventionally to correspond to the quietest sound at 1000 Hz that the human ear can detect.
Reference Time : is used for calculation of Sound Exposure Level and Time Weighed Average with a reference time other than 8 hours.
Refraction : the bending of a sound wave from its original path, either because it is passing from one medium to another with different velocities or by changes in the physical properties of the medium, for example, a temperature or wind gradient in the air.
Residual Intensity : LI,R : the sound intensity level measured when the same signal is fed to both channels of a sound intensity measuring system and is due to phase mismatch between channels.
Residual Noise : this is ambient noise without the specific noise. It is the noise remaining at a point under certain conditions when the noise from the specific noise is suppressed.
Residual p-I Index : the residual pressure-intensity Index describes the phase mismatch between the two channels used for sound intensity measurements. It is equal to the mean pressure minus the intensity with the probe in a sound field where the pressure is uniform over the volume containing the microphones - for example, using Sound Intensity Calibrator B&K type 4297.
Resonance : resonance is the tendency of a mechanical or electrical system to vibrate or oscillate at a certain frequency when excited by an external source, and to keep oscillating after the source is removed. If something tends to have resonance it is said to be resonant.
Resonant Frequency : the frequency at which resonance occurs.
Reverberant Field: the region in a room where the reflected sound dominates, as opposed to the region close to the noise source where the direct sound dominates. The same as diffuse field - see also far field : near field
Reverberation: sound that persists in an enclosed space, as a result of repeated reflection or scattering, after the sound source has stopped.
Reverberation Chamber : a specially constructed test room in which all the surfaces are hard and reflective so that none of the noise produced will be lost by absorption, often used for the measurement of sound power levels of noisy machines.
Reverberation Time : RT60 or T60 - the time it takes for the sound pressure level to fall by 60 dB after the sound has been turned off. Measuring reverberation times enables the calculation of the total sound absorption. The reverberation time varies according to the frequency.
RMS : Root-Mean-Square : of a time-varying quantity is obtained by squaring the amplitude at each instant, obtaining the average of the squared values over the interval of interest, and then taking the square root of this average. For a sine wave, if you multiply the RMS value by the square root of 2 (1.414), you get the peak value of the wave. The RMS value, also called the effective value of the sound pressure, is the best measure of ordinary continuous sound, but the peak value is necessary for assessment of impulsive noises. Also, used to describe the mathematical process of determining the average value of a complex signal.
RMS averaging : averaging technique used to average the energy, or power, of a signal. RMS averaging reduces signal fluctuations but not the noise floor. RMS averaging for dual-channel measurements is defined in such a way to preserve important phase information.
Room Absorption : sum of Sabin absorption due to objects and surfaces in a room, and due to dissipation of energy in the medium within the room.
Room Absorption Coefficient : ratio of Sabine absorption of a surface to the area of the surface.
Root-Mean-Square : RMS
rpm : revolutions per minute. :
RT : Reverberation Time.
RTA : Real Time Analyzer.
RT60 : : Reverberation Time.
R : Sound Reduction Index : the measured quantity which characterises the sound insulating properties of a material or building element in a stated frequency band - laboratory measurement.
R' : Sound Reduction Index : the measured quantity which characterises the sound insulating properties of a material or building element in a stated frequency band - field measurement.
Rw : Weighted Sound Reduction Index : a single-number quantity which characterises the airborne sound insulation of a material or building element over a range of frequencies - based on the laboratory measurement of R.
R'w : Weighted Sound Reduction Index : a single-number quantity which characterises the airborne sound insulation of a material or building element over a range of frequencies - based on the field measurement of R'.
GLOSSARY INDEX:
A B C
D E F
G H I
J K L
M N O
P Q R
S T U
V W X
Y Z
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