B&K 2250 Light, User Manual, Page: 192 / 208

2250 Light – User Manual 182
SIL, PSIL, SIL3: SIL (Speech Interference Level) is the arithmetic average of the 500 Hz,
1 kHz, 2 kHz and 4 kHz octave band levels.
PSIL (Preferred Speech Interference Level) is the arithmetic average of the
500 Hz, 1 kHz and 2 kHz octave band levels.
Used for evaluating the interference of noise upon speech communication.
SIL3 (Speech Interference Level based on highest 3 octaves) is the arithmetic
average of the 1 kHz, 2 kHz and 4 kHz octave band levels.
Note: Though SIL, PSIL and SIL3 are defined for octave band levels they
are also calculated for 1/3-octave band levels by summing the power values
in the three bands within each octave before doing the averaging.
Sound: Any pressure variation that the human ear can detect. Just like dominoes, a
wave motion is set off when an element sets the nearest particle of air into
motion. This motion gradually spreads to adjacent air particles further away
from the source. Depending on the medium, sound extends and affects a
greater area (propagates) at different speeds. In air, sound propagates at a
speed of approximately 340 m/s. In liquids and solids, the propagation velocity
is greater – 1500 m/s in water and 5000 m/s in steel.
Sound level or sound
pressure level: The level in decibels of the pressure variation of a sound. See also decibel .
Std.Dev. The Std.Dev. is calculated as the Standard Deviation of the noise samples
used for statistics. This is either L
AF
or L
AS
sampled every 10 ms or L
Aeq
sampled every second.
T
Cpeak
: The time when the peak sound level occurred. ‘C’ denotes that the
C-frequency weighting is used.
Threshold Level: Any sound levels below the threshold level do not contribute to the Dose
measurement data. For example, if you set the threshold level to 80, any
sound levels below 80 dB are not taking into consideration by the instrument,
when it calculates doses and time weighted averages.
Used for calculation of Dose, ProjDose, TWA, TWA
v
DoseSQ, ProjDoseSQ.
TWA: The Time Weighted Average is the average A-weighted sound level for a
nominal 8-hour working day with Time Weighting S and Exchange Rate 5.
TWA is calculated from the measured LavS5 (taking Threshold Level into
account) and a Reference time of 8 h. Mainly used in the USA for assessing
the noise exposure for a worker during a working day.
TWA
v
: The Time Weighted Average for a user-defined reference period. TWA
v
is
calculated from the measured LavS5 (taking Threshold Level into account)
and the Reference Time. Used, for example, for calculating a Weekly Time
Averaged Level by setting the Reference Time to 40 h.
Z-weighting: ‘Zero’- frequency weighting is without any frequency weighting, that is,
equivalent to Linear, LIN or FLAT.