Criterion Level Constant sound level that, if applied for 8 hours, would accumulate the allowable dose of 100%
Decibel (dB) A dimensionless unit equal to 10 times the logarithm to the base 10 of the ratio of two values. In occupational noise measurement, decibels are usually measured in terms of sound pressure, and referenced to 20µPa. Decibels defined in terms of sound pressure level (SPL) represent 10 times the log to the base 10 of the ratio of the square of the sound pressure in Pa to the square of the reference sound pressure of 20 µPa:
SPL = 10 log (pressure^2/reference pressure^2)
This is equivalent to:
SPL = 20 log (pressure/reference pressure)
Equal Energy Hypothesis A hypothesis stating that equal amounts of sound energy will produce equal amounts of hearing damage, irrespective of the distribution of the sound over time
Exchange Rate (ER) Number of dB required to halve or double the allowable exposure duration. For instance, using a 3 dB exchange rate, an individual could be exposed for 8 hours at a constant sound level of 85 dB, or 4 hours at a constant sound level of 88 dB
Frequency Weighting Method of applying frequency-specific weights to any noise measurement. Three weighting networks are available: A, B, and C. A-weighting closely imitates the spectral response of the human ear to sound frequencies, deemphasizing lower and higher frequencies (0-1000 and 5000-16000 Hz)h and emphasizing mid-range frequencies (1000-5000 Hz)
Impact/Impulse Noise Defined by OSHA as a sound with a rise time of not more than 35 ms to peak intensity and a duration of not more than 500 msec to the time when the level is 20 dB below the peak. Impulses recurring at intervals of less than 0.5 s are considered continuous noise Impulse noise has been described as "a noise transient that arises as the result of a sudden release of energy," while impact noise has been described as "a noise transient that arises as the result of the impact between two objects (Hamernik et al, 1991)." Impact noise may be viewed as reverberant, while impulse noise may be considered nonreverberant
LEQ The average sound level measured during a given period based on a 3 dB exchange rate and defined as the equivalent average exposure level
LOSHA The average sound level measured during a given period based on a 5 dB exchange rate
Maximum Level Maximum weighted sound pressure, in dB, with application of response time constant
Noise Unwanted sound
Peak Level Maximum instantaneous unweighted sound pressure, in dB
Response Time Time constant, or exponential averaging time, applied continuously to sound pressure measurement. Two response times are available: SLOW (1.0 s time constant) and FAST (0.125 s time constant)
Threshold The sound pressure level above which sound pressure measurements are integrated into a noise exposure dose, and below which measurements are recorded as ‘zero’ readings
Time Weighted Average (TWA) The sound level in dB accumulated for any time period but with an average level computed over an 8 hour time period
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