Microphone electronic parts + impedance

Discussion in 'General Electronics Chat' started by veenife, Mar 11, 2014.

  1. veenife

    Thread Starter Member

    Jan 16, 2014
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    ive been looking how dynamic microphones are build and stuff.... till now i couldnt really find anything describing what electronic parts a microphone has...

    .. one thing that im more interested is about the output impedance of the microphone....
    so as impedance will come from inductors, capacitors and resistors.... where in a dynamic microphone are this parts build and what exactly are they serving to?
     
  2. #12

    Expert

    Nov 30, 2010
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    Why do you think a microphone has capacitors and resistors?

    A dynamic mic has a coil that is driven by a magnet.
     
  3. veenife

    Thread Starter Member

    Jan 16, 2014
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    yeah that part i get (coil magnet)... but it aint just it, right???
    i've heard that they do have a transformer....
    but what else (electronic parts ) is build inside the mic then???

    i cant grasp where the mic's impedance is coming from if no capacitor or inductors are build in it......
    ????

    or maybe ... is it coming just from the coil itself??? which yeah, it is a sort of inductor.... hm....
     
  4. #12

    Expert

    Nov 30, 2010
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    Some of them have a transformer. Some of them have a jfet amplifier inside. Most of them don't have capacitors or resistors. What's your theory...that microphones are all zero ohm impedance until some more parts are added?

    Name one. This conversation can't make sense if we're trying to classify all forms of microphone at the same time.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the coil in the microphone is the inductance. you will find that a lot of "audio" mpedances are more of a range than an actual impedane. the dynamic mics with transformers usually have them to step up the impedance to that of a crystal mic.
    dynamic mics are usually called 600 ohm impedance, crystal or ceramic are usually around 10,000 or higher. amplified mics are what ever the manufacturer says they are.
     
  6. veenife

    Thread Starter Member

    Jan 16, 2014
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    yeah its already a relief to know that the impedance comes from the mics coil.... dont know how i didnt realize that before....

    but why the need of a transformar to step the impedance up?

    ive learned that the lower the mic impedance is, the better it will be to avoid trasmition loss... so why is that?

    ... most pro mic will have their output impedance with values around 200 ohms....or??? but like 600 and 10 000 thats way too much....



    but going back to the coil impedance subject ...i assume then that a dynamic microphone impedance will be mostly inductive.... as inductive reactance is proportional to frequency... (the higher the freq. the higher the inductive reactance) ... does it mean that a dynamic microphone frequency response will be attenuated on high frquencies???
     
    Last edited: Mar 11, 2014
  7. #12

    Expert

    Nov 30, 2010
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    Why the choice of a transformer to step up impedance? To step up voltage.
    The lower the impedance the less noise it will pick up in the wires. It's not about transmission loss. It's about signal to noise ratio. A good signal to noise ratio at a low impedance is the ideal situation for an amplifier to work with.

    Attenuation at high frequencies? Depends on how you make the coil and how you attach the load to the coil. Microphones are intentionally designed to have full bandwidth, or not. Depends on which response characteristics you need. Micing a cymbal is a very different job from micing a person.

    The high impedance theory uses high voltage to get a good signal to noise ratio. The low impedance theory uses the immunity to picking up radiated noise to get a good signal to noise ratio.
     
  8. veenife

    Thread Starter Member

    Jan 16, 2014
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    okay, but i guess output impedances of 600 ohms or higher arent really desired on the audio industry for a while anymore, right?... i mean back then when the matching impedance standard was the deal, but these days if you check any mic specification you can see that most of them dont go over 300 ohms.... and most amps try to have their input ipemdance as big as possible...

    and the transfomrer....as an example... shure 57... the mic does have a transformer and its output impedance is anyways 150 ohms.... does it mean that the real impedance from the 57 is even smaller then that and the transformer is bringing it up to be 150 ohms?

    and again about the coil... inductance changes its value depending on the number of turns that the coil has and the coils diameter....

    so for example a kick mic....a kick mic is usually much bigger than a vocal mic... i assume that is so because making the diameter from the coil big, inductance will be higher...and so letting the mic being more sensitive at low frequencies.... is that right??
     
  9. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    No, most of the impedance comes from the actual resistance of the wire in the pickup coil, just like in speakers where an 8 ohm speaker measures usually around 5-6 ohms with ohmmeter.

    Kick microphones are big, because the diaphragm needs to be big to get better low frequency response. Again just like in speakers - larger speakers are better at reproducing lower frequencies, but worser at high frequencies because of the mass of the larger diaphragm.
     
  10. veenife

    Thread Starter Member

    Jan 16, 2014
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    alright, nice! ...
    so the number of turns in the coil of a microphone must be very small if impedance will come from the resistance of the coils wire.... right?

    i know that guitar pickups have thousands of turns....

    how many turns a mic coil will have then more or less???
    i assume it must be very little if its impedance comes from the wires resitance....
    doenst the inductance from the coil play any roll on the impedance value???
     
    Last edited: Mar 11, 2014
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    The number of turns in a typical dynamic mic is I´d guess somewhere around 50-200 but the wire needs to be very very thin to keep the total mass really small, so even a few turns can produce quite high resistance.
    The weight of the diaphragm and coil has some inertia to it, so the higher weight it has the leser the fast sound waves can move it, so the high frequency response is going down with added weight.

    Guitar pickups are right on the other side, where they have somwhere around 100 kiloohm resistance, but they have awful lot of wire wound to generate enough voltage to get it above the noise induced into the long cable runs.
     
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