can you suggest a transducer to pick up a signal .

hi thank you for readin this message.
can you tell me which transducer is to be used to pick up a signal from
any electronic circut .i am designing a noise measuring device .
ranging from 4Khz to 10Khz.
having a preamplifier ,filter,precision rectifier,averager/scaler,and display
can you suggest me something in this i have only block diagram no circiut diagram is still available
.
thanks for reading this

It really depends on the type of environment u want to use the tranducer into. If the noise fluctuations are significant maybe a simple inductive transducer would do. Also what is the basic functioning of the existing ckt?