Formula to calculate speaker impedance

[Perry Babin]

I'm looking for the formula that will allow me to plot the impedance curve of a speaker including the peak at resonance.

Thanks in advance
Perry Babin

 

[roddyama]

Hi Perry,

This link will tell you how to measure the speaker impedance.
http://www.epanorama.net/documents/audio/speaker_parameters.html

 

[Perry Babin]

Hi Rodd,

Thanks for replying. What I'm looking for is the formula that will give the impedance vs frequency curve when the T/S parameters are plugged into it. I've never seen it anywhere but I'd assume that it would use suspension compliance, moving mass, voice coil resistance, voice coil inductance and frequency. I want to build a Flash demo with it but I can't find the formula.

Thanks again
PB

 

[Ron E]

Motional Impedance is the characteristic polynomial divided by the characteristic polynomial with Qm substituted for Qt.

Now you just need the transfer function and to patch in the VC inductance portion

 

[Perry Babin]

I'm sorry to say that I didn't understand anything in the first paragraph. Can you explain in a little more detail?

I remember polynomials like X^2+5x+2 from algebra but I don't know how that applies to this.

I know that I'm asking a lot but I haven't found any other forum with people as knowledgable as those here.

Thanks again
PB

 

[roddyama]

Perry,

Small derives this equation in early 70's paper on Direct Radiating Loudspeakers. You can get a copy of these papers through Audioxpress here:
http://www.audioxpress.com/bksprods/bookindexl3.htm
You'll want to look at "Loudspeakers Vol. 1".
Although Small does a great job of extracting and presenting the concepts from the math, the math itself is not trivial. It's relatively advanced stuff.