[ProAudio] Microphones question

Jim Brown jim at audiosystemsgroup.com
Fri Jun 11 20:25:10 PDT 2021

On 6/11/2021 6:47 PM, Bill Whitlock via ProAudio wrote:
> As I recall from my tests of the SM57, its impedance varied from under 
> 150 Ω at very low frequencies to over 300 Ω at resonance - and continued 
> to rise at higher frequencies.  I'll try to find the data - I did the 
> tests as research before writing Jensen AN-005 about mic splitters.

I remember seeing that data, perhaps in your chapter in the Ballou 
Handbook for Sound Engineers.

To others -- it's important to realize that the impedance of a dynamic 
mic is complex, because it's equivalent circuit is complex. Remember 
that a dynamic mic is the analog of a single driver loudspeaker. If I 
remember correctly, the nominal impedance of a mic is defined by the 
manufacturer as 1/5 of the minimum load impedance. Someone will correct 
me if my memory has failed me. For loudspeakers, it's the minimum value 
of its impedance when plotted vs frequency, and it's impedance typically 
varies by at least two orders of magnitude over its operating range.

Jim Brown

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