Thanks Ray,

   After piecing the facts this is what I gather.
The inductor in the buzzer has some capacitance.

http://www.faqs.org/docs/electric/AC/AC_6.html

The last diagram. It explains:
Fresp = 1/(2*pi * ((L*C)^1/2));

There is no capacitor within the circuit. The
capacitance comes from the inductor itself. 

Still does not explain the resistor very well with
that formulae. 

http://www.play-hookey.com/ac_theory/ac_rlc_series.html
Now this explains the resistor part.
Section:
Resonance and the Effect of R


Finally we have this nice formulae:
http://qbx6.ltu.edu/s_schneider/physlets/main/rlc_resonance.shtml


The last link was a bit ahead of my understanding.
Once again maximum power theory but with a twist of 
(Resonance) in Series RLC Circuits.


If I have misunderstood any concept please correct me.

Big thanks Ray,
John







--- Ray Newman <list@microdesigns.biz> wrote:

> John,
> You have to match the natural resonance of the
> buzzer.
> Putting a resistor is series allows it to try and
> resonate.
> If you ac couple and adjust frequency, you will find
> it gets louder as
> you approach the resonance frequency.
> Ray
> 
> 
> On Sun, 1 Apr 2007 21:30:34 -0700 (PDT), John Chung
> wrote:
> > I have been trying to understand the theory of why
> my
> > buzzer is not working as it is suppose to be*at
> least
> > to my understanding*.
> >
> > I managed to salvage a buzzer from a PC. It looks
> some
> > thing like this.
> >
> >
http://www.rdiusa.com/products/Audio/DMT-12%20Srs.html
> >
> > On the component it does not state the
> manufacturer so
> > I was left to identify the type of buzzer.
> Magnetic or
> > piezo. I applied the buzzer leads across the PIC
> i/o
> > pins PORTA 0 and ground. I checked the current
> > consumption during Q and it was draining about
> 32mA.
> > That was when I concluded that it was a magnetic
> > buzzer like the link above due to the coil.
> >
> >
> > I measured the resistance of the buzzer which was
> 15
> > ohms. Now I pulse my i/o pin and there was no
> audible
> > sound. When I place a resistor in series with the
> > buzzer I can  hear an audible sound from the
> buzzer.
> > Now comes the question. Why do I need a resistor
> in
> > series? It is due to the time constant of the coil
> > that I need to reduce it?  t = L/R? Currently it
> does
> > not make sense here.
> >
> > Can anyone help me understand the theory behind
> this?
> >
> > Thanks,
> > John
> 
> 
> 
> > -- 
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> 



 
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