SPL (Sound Pressure Level)

General

– Variations of Ambient Pressure caused by a Sound Wave

– 20 Micro Pascals

– Logarithmic Measure of the Changes in Pressure Relative to a Reference Level

– Threshold of Human Hearing, means a SPL Meters “Ear” (Input Threshold of Microphone) is similar to our Ears Reaction on Real World Sound Waves / Noise

– Human Hearing Ranges in General from 0dB to 120dB

– Consider that Human Hearing is Not Linear in Pitch, Higher Frequencies are Perceived Louder than Lower Frequencies

– Consider that Human Hearing is Not Linear in Loudness as well, Perceived Equal Changes in Level require Doubling or Halving the Pressure 

– and Perceived Loudness depends on Duration, so Longer Tones Sound Louder than Shorter Tones

– There is a “Equal Chart Contour” for Perceived Loudness by Fletcher and Munson

– to Measure Sound Pressure there are “Filters” built In to Compensate what our Ears Tend to Do, these are A,B,C Weighting

A = Background and Noise Measurement (Equivalent to Linear Hearing at 40dBspl)

C = Sound System Calibration (Equivalent to Linear Hearing at 100dBspl)

Weighting Contour A,B,C (SPL)