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In Reply to: RE: What do you make of this? (Impedance curves) posted by pix on March 04, 2017 at 07:44:06
the cabinet type and woofer/subwoofer characteristics need to be stated. the rise at 20Hz could be the lower impedance peak of a large vented cabinet with low Fs woofer tuned a bit "high" (~32Hz) - if so, Z should drop towards Re as it goes down below 20Hz.
A 10 ohm resistor could be compared with the meter at each frequency of interest to correct any non linearity in the meter and allow even cheap meters to work. Just adjust so it reads "10" with the resistor in place, then measure the speaker. Something is flattening or appearing to flatten out the impedance. It takes a function meter or sine generator with fine increments to do it by "hand".
Edits: 03/04/17Follow Ups:
I appreciate that you share your kwnoledge. I am a newbee in this measure topic, and I am trying to learn ;o)
Linked are the woofer characteristics (Beyma P1580Fe). The cabinette is a Karlson K-15, built by the original drawings (including the very low amount of damping material inside the cab). The slot dimensions are according to the drawings. Note that the filter includes a handwired aircored 4mH autoformer (Taped to lower the mid horns 11dB), which may influsence the Zin a bit.
This measure is done at the complete speaker through the filter input (Karlson K-15/Beyma 15P18Fe, 200Hz Horn/Radian 750Pb, Fostex tweeter).
Also, worth mention is that my 300B SE tube amp used for this measure (not sure if this is influencing the measures).
I have the speakers at my countryhouse and will not be able to measure them further untill next weekend. My plan is to measure from DC and up, to see if the 20Hz rise is a peak or not.
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