I've been using them for years, As above, put them on, you'll like the improvement , take them off for a listen and it'll be brief, they go back on. More natural, less extraneous "stuff". Well worth it.
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!
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