Hi Pete, thanks for the reply.
First off I mentioned Win ISD which was a mistake, I'm using REW for analysis.
I did measure Fs with a stand alone generator and frequency counter, ironically I found Fs to to go down with drive voltage.
This is one of the 15 ohm Seas drivers:
Drive Voltage Fs
100mV 37Hz
200mV 37Hz
300mV 36Hz
400mV 36Hz
500mV 35Hz
600mV 35Hz
700mV 34Hz
800mV 34Hz
900mV 33Hz
1V 33Hz
1.5V 31Hz
2V 30Hz
2.5V 29Hz
REW runs their Z at 100mV. Yet their value is what I measured at 1V.
I did verify accuracy, I used a measured 21.1 ohm resistor and REW reports back 21.1 across the frequency spectrum.
I do have a scope, will take a look at the waveform.
How did you measure your driver - manually or with another program?
Thanks!