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Just ran some numbers through Mathematica

Posted by Mart on May 6, 1999 at 01:47:30:
I toke my Morel MDT40 T/S parameters:
Re = 5.45ohm
Le = 0.05mH
fs = 700hz
f1 = 500hz
f2 = 1kHz
Zmin = 6.0ohm
Zmax = 9.9ohm
 +---Cs---+
 |  |
0---+---Rs---+---Re---Le---0
 |  |
 +---Ls---+
where:
Rs = Zmax - Re = 4.45ohm
Cs = 1/(Re*2*Pi*f2) = 29.2uF
Ls = Re/(2*Pi*f1) = 1.735mH
I wired a notch filter but virtually nothing happened, which could be expected due to the small size of the impedence spike & the couple octaves distance away from the XO point. I then wired a Zobel of:
0---Cz---Rz---0
where:
Rz = Zmin = 6.0ohm
Cz = Le/Rz/Re = 1.529uF
And, low & behold, a 2dB boost occurred between 5-10kHz, up & disappeared by installing a Zobel. Mind you, an 8kHz reasonant interplay between the XO cap & the voice-coil inductance was overted by the Zobel. In fact, the response curve resembles a unit Q 2nd-order XO roll-off knee.