4/7/2024 0 Comments 20a decibel scale![]() "Noise" (unwanted sound) became a public issue. The advent of "talkies" - film sound - was a big stimulus to sound meter patents of the time, but there was still no standard method of sound measurement. The first electrical sound meter was reported by George W Pierce in Proceedings of the American Academy of Arts and Sciences, v 43 (1907-8) A couple of decades later the switch from horse-drawn vehicles to automobiles in cities led to large changes in the background noise climate. "B" Weighting is now little-used, but C-Weighting has achieved prominence in evaluating annoying community noises such as low frequency sound emitted by artillery fire and outdoor rock concerts. "B" and "C" Weightings reflect this trend. When sound is very loud - 100 dB or more, the perception of loudness is more consistent across the audible frequency band. Unfortunately, human perception of loudness vis-à-vis frequency changes with loudness. Section 8.2 shows a table of these weightings. By using an electronic filter of attenuation equal to that apparently offered by the human ear for sound each frequency (the 40-phon response curve), the sound level meter will now report a numerical value proportional to the human perception of the strength of that sound independent of frequency. In EE parlance, the "3 dB" rollover frequencies are approximately 500 Hz on the low end and 8 kHz on the high end. The eardrum- stapes-circular window system behaves like a mechanical transformer with a finite pass band. Yet our ear perceives low frequency sound to be of less loudness that higher frequency sound. The following is from the FAQ of Campanella AcousticsĪ sound level meter that measures the sound pressure level with a "flat" response will indicate the strength of low frequency sound with the same emphasis as higher frequency sounds. What is difference between dB SPL and dB(A) SPL?
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