Sometimes we design and make circuits which function correctly in pieces but when the circuits are connected together, they do not give the expected result. For example, design a low frequency oscillator such as a Wien bridge oscillator and a common collector amplifier. Check their functioning separately and then connect the output of the oscillator to the input of the amplifier. If the design of the amplifier is not meticulous, most probably the output will not be as expected. This may be due to ignorance of a simple but a very important concept called impedance matching. So what is impedance matching?  To understand this let us take a classic example where impedance matching is used, sound amplification using a microphone and a loudspeaker.