need help with frequency sensitive microphones

hey guys... i am trying to make the serb move on sound frequncies.. however i am facing some problem with the microphones.. some how the serb is not responding as it shud to even the extreme of frequencies.. n the readings are bit random.. can someone please suggest a solution or tell me which microphones should be used which would be sensitive enough...
also.. the readings on the serial monitors are numbers varyin between 300 to 900..can someone help me with some factors or co-efficients to convert these numbers in to tangible frequency readings if that is possible?
thanks... urgent replies please!!!!!!!!!

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