Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Tman]

why do we use low impedance mics in reinforcement? the real reason?

[John Roberts {JR}]

Tman wrote on Fri, 22 April 2005 17:28

why do we use low impedance mics in reinforcement? the real reason?

"Real reason" ?? Do you expect a funny answer just because you post a newbie technical question in a product review section?  

There are a few advantages to low impedance (AKA low Z) mics in sound reinforcement. First, the lower source impedance of the microphone will generate less self-noise due to random heat induced electron motion. This thermal noise in resistances is also called "Johnson Noise".

Secondly, a high frequency roll-off (LPF) will be created by the interaction of the microphone's source impedance and accumulated cable capacitance. Keeping the microphones impedance low helps mitigate the capacitance of heavily shielded cable. Bad in the "ole days" movie sets sometimes used special even lower impedance microphones to deal with very long cable runs.

Thirdly, having the source impedance low wrt the preamp's input impedance will reduce signal losses, and damp some other noise sources associated with the preamp.

JR

[Mac Kerr]

Come on JR...why are they really low impedance?

Mac

[John Roberts {JR}]

They're not really low impedance... moving coil phono cartridges were on the order of 10-20 ohms... that's really low.

JR