Audio and AC frequency

[veenife]

Hi,

I`m doing at the moment an essay about how impedance affects the frequency response of dynamic microphones...
like, if a preamp has high or low input impedances it will change the way the microphone captures the audio frequencies....

I`m going through all the basics of electronics.... and something I can`t understand yet is the relation between an AC circuit frequency and audio frequency...


for example:
it`s known that the amount of reactance of a capacitor varies due to the size of its circuits frequency....

and i think:
then when a sound wave reaches a mic, its then transformed into equivalent electrical frequency ...

so then the capacitor will be filtering some frequencies depending on the audio frequency size(equivalent electrical frequency) .... or??

as you can see im totaly confused...

BASICLY, i want to understand how reactance/impedance affects audio frequencies.....

any help will be welcome... suggestions for books and etc...

 

[Audioguru]

A series capacitor from the mic to the preamp is a highpass filter. It cuts low frequencies. The formula is simple. A series capacitor is also a highpass filter inside amplifiers.

A dynamic mic has a low frequency resonance at 100Hz-200Hz and a high frequency resonance at about 5kHz. If the input impedance of the preamp is high then the resonances produce a certain colored sound. If the input impedance of the preamp is the same as the mic or lower then it damps the resonances and the mic sounds like it has a flatter frequency response.

 

[veenife]

alright... thats very good info.... i never heard before from the low and high resonance frequencies... thats an important point i was missing....
tx!!!

is any book where i can get to know more in details this thema???

but what about the frequency from an AC circuit and audio frequency, whats the correaltion between both???

 

[Audioguru]

i never heard before from the low and high resonance frequencies.

Why don't you look at the frequency response curve of a dynamic mic?

this thema???

What is "thema"?

but what about the frequency from an AC circuit and audio frequency, whats the correaltion between both???

An AC circuit moves electrons back and forth.
An audio frequency moves electrons or air molecules back and forth.
A series capacitor feeding a resistance to ground is a highpass filter.
A series resistor feeding a capacitance to ground is a lowpass filter.

 

[veenife]

ok,

the point of my question is more like.... sound waves come in the air hit the microphones membrane... then the coil moves, creates changes on the electric field thats happening inside the moving coil system...

then the sound frequency will have an equivalent electrical frequency in the circuit, which will be distorted/filtered inside the electronic circuit before been reproduced again by the speakers....

capacitors will have a bigger reactance if the circuit`s frequency is low... inductor have a bigger reactance if the circuit`s frequency is high....

so does "audio frequency" can be distorted/filtered inside a circuit just because of the circuit`s voltage, current frequency amount????

do i make any sense?

 

[Audioguru]

The reactance of a capacitor or an inductor is its AC resistance at a certain frequency.
The crossover network in a hi-fi speaker uses capacitors and inductors as filters so that only high frequencies go to the tweeter and only low frequencies go to the woofer. Instead of using LC filters in the speaker amplifiers can have RC filters inside.