09 ATTACHMENTS - Laserfiche WebLink

Pam Hardy Apri19, 2008 Page 3 TABLE 1 Definitions of Acoustical Terms Used in this Report Term Definitions Decibel, dB A unit describing the amplitude of sound, equal to 20 times the logarithm to the base 10 of the ratio of the pressure of the sound measured to the reference pressure. The reference pressure for air is 20. Sound Pressure Level Sound pressure is the sound force per unit area, usually expressed in micro Pascals (micro Newtons per square meter), where 1 Pascal is the pressure resulting from a force of 1 Newton exerted over an area of 1 square meter. The sound pressure level is expressed in decibels as 20 times the logarithm to the base 10 of the ratio between the pressures exerted by the sound to a reference sound pressure (e.g., 20 micro Pascals). Sound pressure level is the quantity that is directly measured by a sound level meter. Frequency, Hz The number of complete pressure fluctuations per second above and below atmospheric pressure. Normal human hearing is between 20 Hz and 20,000 Hz. Infrasonic sound are below 20 Hz and Ultrasonic sounds are above 20,000 Hz. A-Weighted Sound Level, The sound pressure level in decibels as measured on a sound level meter dBA using the A-weighting filter network. The A-weighting filter de-emphasizes the very low and very high frequency components of the sound in a manner similar to the frequency response of the human ear and correlates well with subjective reactions to noise. Equivalent Noise Level, The average A-weighted noise level during the measurement period. The L~ hourly L~ used for this report is denoted as dBA L~m~. Community Noise The average A-weighted noise level during a 24-hour day, obtained after Equivalent Level, CNEL addition of 5 decibels in the evening from 7:00 pm to 10:00 pm and after addition of 10 decibels to sound levels in the night between 10:00 pm and 7:00 am. Day/Night Noise Level, The average A-weighted noise level during a 24-hour day, obtained after La° addition of 10 decibels to levels measured in the night between 10:00 pm and 7:00 am. Loy, L,o, Lam, L~ The A-weighted noise levels that are exceeded 1 %, 10%, 50%, and 90% of the time during the measurement period. Ambient Noise Level The composite of noise from all sources near and far. The normal or existing level of environmental noise at a given location. Intrusive That noise which intrudes over and above the existing ambient noise at a given location. The relative intrusiveness of a sound depends upon its amplitude, duration, frequency, and time of occurrence and tonal or informational content as well as the prevailing ambient noise level.