Nikongod, I changed electrolytics to 5600uF improving the phase distortion in low frequencies
Well, I did some research ...
both p and s drivers himself has impedance of 5 ohms. Added to this the cable (2 Ohms) and a resistor (20 Ohms to the p and 100 Ohms for the s).
Thus, the total impedance of the p is 27 Ohms and the s is 107 Ohms.
Through data of this link
Etymotic Research, Inc. - ER-4 - Technical Specifications could do some math. Then I obtained that The driver's real sensibility ( 113.6 db/mW ) and the maxim continues voltage (140mV rms).
Using spice to simulate the circuit I obtained a voltage of 44.5mV with o.ooo% distortion at 1khz. This would give 95db spl.
With one very high entrance voltage I would have an exit maxim voltage of 58mV rms with a hard clip. This would feel well below the 140mV rms continuous that the drive support.
Here the small phase distortion
Well, I do not be any smart in electronics and know that simulation is never the real thing. Then if anybody knows about any reason for this do not work let me know.
Thanks!