DIY Impedance Control; Condenser Mic

Those devices put a resistor between pin 2 and pin 3, raising the load to the microphone. Since a dynamic mic is like a dinamo, it has some electro-mechanical effects, braking the moving diaphragm. Then you obtain some differences in sound, i.e. a reduced sensitivity to handling noise and an attenuation of low frequencies, because the microphone has an inductive output.