Phil Allison wrote:

"John Stewart"
Phil Allison wrote:


About a year & half ago I built a Loud Speaker Simulator very much like
that shown in Phil's article. For the input L I have a 90 microhenry
aircore
choke followed by a 7.5R, 10 watt resistor. The low freqency resonance
is formed
by a Mallory 220 microfarad NP motor starting cap in parallel with a
Hammond
159ZC choke ( 60 mh, 0.7R).


** Such a low value for the input L means you are effectively simulating
a
speaker that has a copper cap ( inductance damper) on the pole piece -
ie
as is commonly used for wide range or twin cone speakers.

The bass resonance is at 44 Hz but the peak current before saturation is
only 2 amps for the 159ZC, so power input is a bit limited.



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.

........ Phil

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. At the time I built this thing
it was part of another project for which I was working against a time limit.
Checking back I can see the error is both in my schematic & in the text of the
subject article. Luckily, the speaker simulator was only a very small part of a
much larger work.

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

Cheers, John Stewart