Cross-over Pole : So, What defines this term ?

[Earl K]

Hi There

This seems like an opportune time to ask the following questions.
They've puzzled me for a while now.

(i) Just what defines a "pole" in circuit terminology ?
- ie ; Simply & strictly , what electrical conditions must be met for the term to apply ?

(ii) A Zoebel ( a Conjugate RC ) "looks" like it could be a pole in a lowpass circuit / but we all accept that its' never counted or included as such. Why ?


(iii) ( A Conjugate RL )
- Same question . So, what would turn this conjugte RL back into a pole within a HiPass circuit ? ( from the electrical classification point of view)

Thanks for any answers and insights <> EarlK :)

[4313B]

Start here I guess, it's probably as good as any -

http://www.maxim-ic.com/appnotes.cfm/appnote_number/733

http://www.maxim-ic.com/appnotes.cfm/appnote_number/1795

If you have the means to run impedance curves you can see first hand what conjugates/zobels/notches do.

[Earl K]

Thanks for the links !

I'll review them tomorrow ,

- now back to the Masters :D

:cheers:

[Earl K]

Hi There

- I looked through the posted links. I didn't discover what I'm after.
- I'll rephrase the question to see if that jogs anyones memory . Here goes ;

- At which point in circuit design, does an impedance equalizer ( RL or RC ) lose that descriptive designation and instead receive that of an even numbered pole within a typical parallel type crossover ?


<> EarlK

[whgeiger]

Earl,
Answers imbedded {..} in your text below.
For additional information see Rod Elliott’s article [1], particularly Section 3 - Speaker Effects on Filter Response.
Regards,
WHG

)snip(

This seems like an opportune time to ask the following questions.
They've puzzled me for a while now.

(i) Just what defines a "pole" in circuit terminology ?
- ie ; Simply & strictly , what electrical conditions must be met for the term to apply ?

Poles (and Zeros too!)
{Be it a capacitance or an inductance, an energy storage element is required to realize a pole in a passive filter section. In mathematical terms, a pole is a root in the denominator (or a ‘zero’ if a root in the numerator) of the transfer function that characterizes performance of a filter section. The sections addressed below are used to stabilize the frequency dependence exhibited by the driver voice coil impedance. If this dependence is ‘seen’ by the crossover network, filter performance may be significantly degraded. In this role, the purpose of these sections is to maintain crossover filter ‘status quo’ rather than change response slope. A brief functional description of individual circuit topography is provided below.}

(ii) A Zoebel ( a Conjugate RC ) "looks" like it could be a pole in a lowpass circuit / but we all accept that its' never counted or included as such. Why ?

{Lossy High Frequency Inductance Compensation
Given [C1] – [R1] across the loudspeaker voice coil, at low frequencies [C1] appears as an open circuit thus isolating [R1] from current flow. At higher frequencies (where voice coil [Le] and [Re’] are rising), [C1] becomes a dead short thus placing [R1] in parallel with the voice coil and bypassing some current flow around it. The higher impedance, (due to rising [Le] and [Re’]) otherwise seen by the crossover, is reduced due to the presence of the parallel resistor.}

(iii) ( A Conjugate RL )
- Same question . So, what would turn this conjugte RL back into a pole within a HiPass circuit ? ( from the electrical classification point of view)

{Low Frequency Resonance Compensation
Given [L2]-[R2] across the loudspeaker voice coil, at ‘high’ frequencies [L1] is an open circuit thus isolating [R1] from current flow. At lower frequencies (where driver resonance [fs] is approached), [L2] becomes a dead short, and current flows in [R2] thus reducing the impedance seen by the crossover.}

{(iv) For the case not addressed, [C3]-[L3]-[R3] across the voice-coil, only when [L3] and [C3] are dead shorts (or resonate) is [R3] brought into the circuit.}
)snip(
Reference [1]:
Title: The Design of High Quality Passive Crossover Networks
Author: Rod Elliott
URL: http://sound.westhost.com/lr-passive.htm

[4313B]

Thanks WHG! :)

[Earl K]

Yes WHG,

Thanks > that's a great site .

<. :cheers:

[4313B]

I've bought several of his kits over the years.

Still have to finish putting them together. :p