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--. —� arithmetically, and the results then expressed in decibels. The restriction on averaging pertains only to processing of the fundamental pressure squared variable. Statistical processing of sampled derived measurements, such as an ensemble of Leq.T values, is not similarly restricted. The formula used for this task was as follows: Leq.T = 10 log [ 1T OT IOLp(t)/10 dt] = 10 log [Tl OT [ p(t)poJ2dt] To further explain the above formula consider the defining function where Lp (t) is sound pressure levels as a function of time, T is the observation or averaging time, p(t) is sound pressure as a function of time and po is the reference pressure of twenty (20) micropascals ( Pa). Adoption of the equivalent sound level terniinology was likely motivated to forestall erroneous use of the arithmetic averaging. Nevertheless, the term average sound level is also in wide use and is functionally identical. In an actual circumstance where sound levels could be variable, the equivalent sound level equals a constant sound level that appropriately integrated over the averaging time would result in the same energy as integrating the corresponding variable sound level over the same time. In contrast, for sound levels stated for discrete time increments, the overall equivalent level can be obtained by the following combining relationship. The levels for each discrete time period may be constants or may themselves be equivalent levels. Thus the combined equivalent level is (A-weighted levels used in the following example): N LAeq.T = 1 U log [ 1 T ti 10 LAi/10] I =1 The ultimate result of this type of testing is to obtain sound readings that can be used to establish exposure levels. This exposure level of sound dose can also be stated in joules. Regulatory agencies normalize the allowed limit by stating it as percentage dose, where a dose of 100°/o corresponds to an exposure at the criterion level (Lc) for a duration equal to the criterion time (Tc), which is normally specified as eight (8) hours. However, at stated earlier, in this case the target dose will be the immediate, short terni, 100% peak level achieved at any given point dunng the sampling episode. Therefore, the noise level results are all stated in decibels. As such a decibel (dB) is a unit for measuring the intensity of sound. The decibel is a dimension less quantity, based on the logarithm of the ration of two power-like quantities. Considering the human hearing range is theoretically from zero (0) dB (theoretical threshold of audibility) to one hundred and thirty (130) dB, the average pain threshold, a comparison can be shown. Sound power (W) of a source is the total acoustic output that it produces in watts (w). For most practical situations the sound power of a source is constant regardless of its location in different enviro�unents. The amplitude of the sound pressure disturbance can be related to the displacement amplitude of the vibrating sound source. Pressure is expressed as force per unit area. The preferred unit of pressure is known as the pascal (Pa) or one newton per square meter (N/m2).