
Second-order Elliptic Equalizer First Build
Crosstalk Curves for 75, 150, 300 Hz
Left-only input.
Top trace is left out.
Bottom traces are the right channel output with the EEQ switched from 75 to 150 and 300 Hz.

Second-order Elliptic Equalizer Crosstalk Curves for 75, 150, 300 Hz
Comparison of 6 dB vs. 12 dB Per Octave Lateral Versus Vertical Response
Left-only input. EEQ set at 300 Hz.
Top trace is lateral (mono) response.
Bottom traces are the vertical output with the EEQ plotted at 6 and 12 dB per octave.

Second-order Elliptic Equalizer Lateral vs Vertical at 300 Hz with 6 or 12 dB per octave slope
Comparison of 6 dB vs. 12 dB Per Octave Crosstalk Response
Left-only input. EE set at 300 Hz.
Top trace is left out.
Bottom traces are the right channel crosstalk with the EEQ plotted at 6 dB and 12 dB per octave

Second-order Elliptic Equalizer Crosstalk Comparison at 300 Hz with 6 or 12 dB per octave slope
I'll be posting some sound files soon.
Conclusions
1) The steeper highpass slope of the EEQ's second-order vertical response permits, for the same amount of filtering, a lower EEQ frequency to be used.
2) The steeper low pass response of the second-order crosstalk curve improves midrange separation and imaging.
3) Factors 1 and 2 in conjunction lower the crosstalk significantly to maintain midrange stereo imaging.
4) The summed output is mono compatible.
Applications
The applications for the EEQ include vinyl cutting, "bass focus" to improve low-end on headphones, earbuds and small speakers, subwoofer steering and vinyl playback warp reduction.