using an electret microphone to trigger an LED
The circuit works by biasing Q1 so that it keeps Q2 and Q3 cut off. When the microphone generates a negative pulse, the current through Q1 is reduced, its collector voltage rises, and Q2 and Q3 conduct current through the LEDs.

The simplest way to increase sensitivity is to increase the value of R2 until Q1 is just barely keeping Q2 and Q3 off. However, there will be limits on how well this works over a range of temperatures and battery voltages.



A better circuit would use something like a 555, which has a reasonably precise comparator on its input, and provides a well-defined output pulse each time it is triggered:







simulate this circuit &ndash; Schematic created using CircuitLab