Appears to be a Boucherot cell, a.k.a., Zobel network, which can be used to flatten the impedance curve of a speaker. Ideally, they are designed for the specific speaker drivers and they may already be included in some passive crossovers. If you want to design what is essentially a series resistor and capacitor for your specific speakers, something like this might help. I find it interesting that these are intended to be interchangeably used for low, mid, and high frequency drivers. Here is an interesting review of the Synergistic Research XOT Carbon High-Frequency Transducers discussed in the EVS literature.
EVS Music Purifier
Rick Schultz of Tweak EVS has a new product called the Music Purifier.
Read about it here...
http://tweakaudio.com/EVS-2/EVS_Music_Purifier.html
All I can say is wow. Immediately noticeable. For only $125 these are a steal and I highly recommend them.
I have had many of these type of speaker link tweaks over the years, like EVs own Ground Enhancer, the DNM ones, and a few others. All of them did something positive but also took something away. These EVS Music Purifiers seem to be all positive and no negatives. Maybe that will change later on with more critical listening but for now I am impressed.