B&K 2250 Light Manuel d'utilisateur télécharger pdf (Page 194)

Hand-held Analyzer 2250 Light – User Manual186

RC, RC Classification: The Room Criterion Mark II is primarily a diagnostic tool for HVAC noise in

spaces.

The RC curve is chosen as the value of the PSIL, rounded to the nearest

integer, in the range 25  RC  50.

The RC classification is the combination of the Sound Quality Descriptor and

the Probable Occupant Evaluation.

The sound quality descriptor can display the values (N) for neutral, where

no frequency range is dominant; (LF) for rumble, where the low-frequency

range (16 – 63 Hz) is dominant; (MF) for roar, where the mid-frequency range

(125 – 500 Hz) is dominant; and (HF) for hiss, where the high-frequency

range (1000 – 4000 Hz) is dominant. Furthermore, there are two variations

of (LF) if the spectrum in the low-frequency range is likely to introduce

vibrations: (LFVA), where there are clearly perceptible vibrations and (LFVB),

where there are moderately perceptible vibrations.

The probable occupant evaluation describes how an occupant responds to

a spectrum and can have the values Acceptable, Marginal or Objectionable.

Described in the ASHRAE Handbook – HVAC 2011 and ANSI 12.2–2008.

Room Criteria is for rating room noise

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

or L

sampled every 10 ms or L

Aeq

sampled every second.

Cpeak

: The time when the peak sound level occurred. ‘C’ denotes that the

C-frequency weighting is used.

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B&K 2250 Light Manuel d'utilisateur Page 194

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