These three standards are grouped together as they all deal with sound level meters. International standards for sound level meters are accepted by all countries worldwide. They are important because all measurement standards refer to sound level meter standards to define the instrumentation required. In most countries, Type 1 equipment isrequired for environmental noise measurements. • IEC 60651 − Sound level meters (1979, 1993): Defines sound level meters in four degrees of precision (Types 0, 1, 2 and 3). Specifies characteristics including directionality, frequency and time weighting, and sensitivity to various environments. Establishes tests to verify compliance with the characteristics specified. IEC 60804 −Integrating-averaging sound level meters (1985, 1989, 1993): Additional standard to IEC 651 that describes this type of instrument (i.e., those that measure Leq). IEC 61672 − Sound level meters: A new, draft IEC sound level meter standard that will replace IEC 60651 and IEC 60804. Major changes: Tougher specifications, Type 3 disappears. It should mean improved test and quality control of instrumentation andimproved accuracy.
Actual Level New Class 2 Old Type 3 Old Type 2 New Class 1 Old Type 1 000073
Schematic representation of the improvement in accuracy with the new sound level meter standard. The arrows represent the relative measurement error
60 International Standards
A wide range of parameters are used to assess community reaction to environmental noise. The highly variableresponse of individuals to environmental noise and the many characteristics (level, frequency content, impulsiveness, intermittency, etc.) of different types of noise sources has led to many attempts to provide single-number ratings of the effect of that noise. The following list summarises most of the parameters in common usage. “A” frequency weighting: The method of frequency weighting theelectrical signal within a noise-measuring instrument is to simulate the way the human ear responds to a range of acoustic frequencies. It is based on the 40 dB equal loudness curve. The symbols for the noise parameters often include the letter “A” (e.g., LAeq) to indicate that frequency weighting has been included in the measurement.
Noise Parameters and Terminology
Lp (dB) 0 -20 A-40 -60 10 20 50 100 200 500 1k 2k 5k 10k 20k Frequency (Hz) 000074
Fast, Slow and Impulse time weightings: Standardised response times were originally built into noise measuring instruments to provide visual indication of fluctuating noise levels. Environmental assessment standards usually specify which time weighting (F, S or I) to use.
dB Impulse Fast Slow
Time 000075/1Environmental Noise Parameters and Terminology 61
LAeq,T: A widely used noise parameter that calculates a constant level of noise with the same energy content as the varying acoustic noise signal being measured. The letter “A” denotes that the A-weighting has been included and “eq” indicates that an equivalent level has been calculated. Hence, LAeq is the Aweighted-equivalent continuous noise level.Lp Leq
LAE: Sound Exposure Level (SEL): A parameter closely related to LAeq for assessment of events (aircraft, trains, etc.) that have similar characteristics but are of different duration. The LAE value contains the same amount of acoustic energy over a “normalised” one second period as the actual noise event under consideration.
SPL dB (A) LAE(SEL)
L eq 1s
Time 000123/162 Environmental Noise Parameters and Terminology
LAFMax, LASMax or LAIMax: Maximum A-weighted noise level measured with Fast (F), Slow (S) or Impulse (I) time weighting. They are the highest level of environmental noise occurring during the measurement time. They are often used in conjunction with another noise parameter (e.g., LAeq) to ensure a single noise event does not exceed a...