[ProAudio] Microphones question
bobkatz at digido.com
Mon Jun 14 07:45:33 PDT 2021
David: It might also be useful for manufacturers to specify an optimum
load impedance. I heard (anecdotally) that some condensor microphones
perform better with a 10k load instead of a 1500 or 2k load.
On 6/12/21 1:28 AM, David Josephson via ProAudio wrote:
> There is a wide variety of microphone electrical topologies, each with
> distinctly different impedance characteristics, even within the
> “balanced” microphone world. There is an effort underway in AESSC led
> by Anthony Kuzub of CBC to get a little more clarity but I think you
> know about that.
> You asked about the “real” i.e. commonly found, impedance levels. The
> most common topology these days is the so-called “impedance balanced”
> circuit where the microphone feeds audio to either pin 2 or pin 3,
> depending on whether a polarity inversion is required. It is almost
> always through an electrolytic cap and a series resistor of 20 to 50
> ohms. The other audio output pin has the same R and C, but to signal
> return. Phantom power is usually drawn from both signal leads. With
> ideal cables, the CMRR of the preamp produces the same interference
> rejection as if the signal were symmetrical. As it is only the
> impedance is symmetrical. Also relatively common is a pair of pnp
> emitter followers directly connected to pins 2 and 3, with the
> collectors returned to ground through a network held above ground by a
> few volts, to provide a bit of voltage for the input stage of the mic.
> These also typically have a few ohms of resistance, either resistors
> or RFI-suppression chokes in series with each output leg, typical
> impedance is on the order of 40 to 100 ohms. Transformer output mics
> are less common as electret condenser mics have become the defacto
> standard; they are cheaper to make than dynamic elements.
> We have been over this ground dozens of times with the microphone
> manufacturers. The best consensus we can reach is to recommend that
> the manufacturer specify the minimum load impedance, which is
> typically around 1500 ohms.
> David Josephson
>> On Jun 11, 2021, at 7:49 PM, Dan Lavry via ProAudio
>> <proaudio at bach.pgm.com <mailto:proaudio at bach.pgm.com>> wrote:
>> Hi Bill,
>> I am not trying to change the standard. Certainly not before I have
>> the understanding of what is going on. Of course in an ideal world,
>> each mic would come with an impedance information. In a somewhat less
>> ideal world, each mic would come with, at least, the best resistor
>> value. But here we are stuck to the "typical" old dynamic mic.
>> I know that most people don't understand technical details, and it
>> will confuse customers. But I am not talking to customers here, or
>> level playing field. I asked the opinion of mic experts. I want to
>> know what real impedance levels are. That is really all I want to
>> know. So far, I learned about the 150 Ohm relation to the old
>> dynamic. There must be more information, I thought I would start here.
>> Thanks for all the comments
>> Dan Lavry
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