"John Stewart"
Phil Allison

The rise of impedance caused by the 90 microhenry choke starts at about
4KHz & is well up at 10 KHz, similar to a real speaker.

** As usual, you are totally wrong.

Your circuit only rises to 9.4 ohms at 10 kHz while typical woofers have
inductance figures of 0.5 to 2.5 mH - depending on coil size. The
impedance
at 10 kHz is 20 to 30 ohms, unless a copper shorting ring or pole cap is
fitted.

Then the figures are like your circuit.


I think I screwed up in my response, so I will take the easy way out. The
number
is missing a zero & should be 900 microhenries.


** I suspected as much.


As usual, Phil checks everyone's work with a magnifying glass & then
comments
(sort of)!


** Speaker impedance v. frequency behaviour is a topic I have been very
well acquainted with for 30 years - so errors like your stick out like dogs
balls.

In the mid 1970s, I was designing and building SS guitar and PA amps using
single and twin cone speakers. One way a speaker voice coil might become
damaged was if the SS amp broke into supersonic oscillation. The particular
speaker maker I was dealing with here in Sydney believed this to be a common
cause of burnt voice coils on speakers sent back for warranty claims. The
manager tried to deny warranty to me on this basis.

A few simple measurements showed that due to inherent series inductance, it
was totally impossible to overheat the voice coil of the 12 inch driver I
was using any audible frequency with the SS amplifier concerned. The
impedance at 20 kHz rose (from 8) to 24 ohms, the current therefore reduced
to 1/3 and the power dissipation to 1/9 th.

That is true unless the speaker was one of their twin cone types, with a
copper cap on the pole piece, holding the impedance down a high frequencies.




........... Phil