This sound meter or sonometer was found in a Popular Electronics from the 80's. The circuit can be easily implemented today, and the microphone is made of electret or ceramic.
The circuit shown has the advantage over the reductions with resistors to have a much higher...
Originally this circuit is from an English magazine, but I found it in Argentina's Radio Chassis...
This circuit, from an old publication from the 70s, uses neon lamps as indicators and can work on...