Sound, everything was analog and there were no digital readouts, only a needle. Second, it's a holdover from the days of analog sound level meters. First, it is a closer representation of how the human ear perceives sound. Why do we use time weighted sound levels? There are two main reasons. Think of time-weighted sound levels as a kind of running average of sound level. Source for above equation: IEC 61672-1:2013 □ 0 is the reference value of 20 µPa (considered the threshold of human hearing).□ □(□) is the frequency-weighted instantaneous sound pressure signal (where frequency weighting is A, C, or Z).Time in the past as indicated by -∞ for the lower limit of the integral to the time of observation, t □ is a dummy variable of time integration from some.□ is the exponential time constant in secondsįor either the S (slow) or F (fast) time weighting.□ is the frequency weighting, commonly A,C, or Z.Time-weighted Sound Level is defined by the following equation Imagine creating a continuous sound throughout that same period with the same total sound energy as the actual varying sound levels. In other words, the actual sound pressure levels will vary all throughout a measurement period. Where p is the sound pressure and the Measurement Duration (specific time period) is T=T 2-T 1. L eq is the level of a constant sound over a specific time period that has the same sound energy as the actual (unsteady) sound over the same period. Z-Weighting: "Zero" or no frequency weighting applied: in actuality, a passband filter from 10 Hz to 20 kHz.Since 2003, IEC 61672 standard notes use of Z-weighting. Flat weighting indicated that no filter was applied, across a stated frequency range. Flat or Linear Weighting: No longer used in current standards.This weighting is most often used for evaluation of equipment C-Weighting: Commonly used filter that adjusts the levels of a frequency spectrum in the same way the human ear does when exposed to high or impulsive levels of sound.Parameters including dBA, LAeq, LAF, LAS, etc. This weighting is most often used for evaluation of environmental sounds. A-Weighting: A weighting filter that most closely matches how humans perceive sound, especially low to moderate levels.Occupational Noise Evaluation & Industrial Hygieneįrequency weightings are commonly used frequency filters that adjust the amplitude of all parts of the frequency spectrum of the sound or vibration.Portable Noise Monitoring with Sound Recording.Multi-Purpose Environmental Sound Level Meter.