Possibly incorrect impedance measurement

[nemo]

Hello, I am a newbie.
For impedance measurements I use Behringer U-PHORIA UM2, sense ceramic resistor 98.7ohm, and for reference I used three 100ohm ceramic resistors connected in parallel, the resultant resistance was 36,6ohm.
I don't know how my impedance measurements are (in)correct, especially for low frequencies.

Please take a look at these comparisons:
1) B&C 15NW100-4
vs
On my measurement, the first peak (resonance frequency) is 42.5hz@72ohm, but it should be ~33hz@80ohm, yes?
Why this difference?

2) Elac Debut 2.0 B6.2
vs
Why is the impedance at peaks so different? Especially for the first peak?

I attached the .mdat.file
Please explain to me what is wrong and how can I fix it.

Thank you

 

[John Mulcahy]

Your measurements look fine. Driver measurements will vary with the sweep level (specifically the voltage across the driver terminals), the age of the driver, room temperature...