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<p>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.</p>
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</p>
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<p>Bob</p>
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<div class="moz-cite-prefix">On 6/12/21 1:28 AM, David Josephson via
ProAudio wrote:<br>
</div>
<blockquote type="cite"
cite="mid:6C34F502-EE8E-4B21-8748-F0E601A39F0D@josephson.com">
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Dan,
<div class=""><br class="">
</div>
<div class="">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. </div>
<div class=""><br class="">
</div>
<div class="">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.</div>
<div class=""><br class="">
</div>
<div class="">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. </div>
<div class=""><br class="">
</div>
<div class="">David Josephson<br class="">
<div><br class="">
<blockquote type="cite" class="">
<div class="">On Jun 11, 2021, at 7:49 PM, Dan Lavry via
ProAudio <<a href="mailto:proaudio@bach.pgm.com"
class="" moz-do-not-send="true">proaudio@bach.pgm.com</a>>
wrote:</div>
<br class="Apple-interchange-newline">
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charset=UTF-8" class="">
<div class="">
<p class="">Hi Bill, <br class="">
</p>
<p class="">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.</p>
<p class="">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.</p>
<p class="">Thanks for all the comments</p>
<p class="">Dan Lavry<br class="">
</p>
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