My Sound Level Indicator circuit uses an LM3915 that has 10 LEDs with a range of 30dB (3dB each LED). Its input is from a microphone. Ordinary sounds in my home exceed a range of 30dB so my circuit detects when the maximum level is reached then adds another 20dB of range for very loud sounds. 20db is 10 times the signal voltage.
Normally the sensitivity is very high so that the lowest level LED fluctuates when I am breathing, or when the refrigerator or furnace is quietly running but then 30dB more is not very loud and I do not want the loudest level LED lighting continuously with ordinary sounds like conversation or from the stereo or TV. With the total of 50dB of range then very loud sounds cause the upper level LEDs to fluctuate.
Normally the sensitivity is very high so that the lowest level LED fluctuates when I am breathing, or when the refrigerator or furnace is quietly running but then 30dB more is not very loud and I do not want the loudest level LED lighting continuously with ordinary sounds like conversation or from the stereo or TV. With the total of 50dB of range then very loud sounds cause the upper level LEDs to fluctuate.
