I would think a Zobel would imply some type of impedance correction and I can't see how that could be universally applied. Walker's site mentions "very high frequency electronic noises" and RFI. I'm still guessing that it is a low pass filter up around the neighborhood of 20kHz.
Here is a link to a very thorough DIY project where you can build them for yourself. The guy really took time w/photos and sources for parts. It's a 36 page .pdf so it takes a while to load. It's on Alan Mahers site. Check it out!
I bought a set of the series 2 links and tried them on avalon arcus speakers. Did not work well. Sounded as if someone threw a blanket over them. Still have them if anyone wants to buy them.
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