<prompt> Impedance audiometry is done using frequency probe of220 Hz555 Hz440 Hz1000 Hz  <response>: It consists of a probe which fits into the external acoustic canal and has 3 channels: To deliver a tone of 220Hz To pick up the reflected sound a microphone To bring about changes in air pressure in the canal from positive to normal and then negative Ref: Dhingra; 6th Edition; pg no 24 