The amplified microphone is a great way to observe sound waves on an oscilloscope. The output level is much higher than the traditional crystal microphones giving a very clear trace. Two amplified microphones can be used with a storage oscilloscope or Motion QED to measure the speed of sound.Specification:Battery: 3 x AAA (not supplied)Gain: 125Frequency range: 0 - 20kHzOutput :± 2V a.c.