My battle with sibilance.

Mijo, There is a long and very informative thread on the "Gundry Dip", also known as the BBC dip, on Hydrogen Audio.  A few of the contributors are speaker designers or acoustic engineers.  For one thing, it is pointed out that a "natural" dip in frequency response in the 1kHz to 4kHz range is not uncommon among 2-way speakers, where the woofer is giving way to the tweeter in that range.  I urge anyone to read the thread for many interesting tidbits, but the consensus is that the deliberate incorporation of a Gundry Dip in frequency response was a passing fancy, no longer espoused or incorporated so much in modern speakers.  As you suggested, the Gundry Dip is or was a way of incorporating a fixed compensation for the Fletcher-Munson curve, the tendency of humans to be most sensitive to frequencies in the midrange and relatively less sensitive to low bass and treble frequencies.  Why we used to have "Loudness" controls.  A Loudness control makes much more sense than a built-in fixed Gundry Dip in the crossover, because it allows the user to adjust compensation according to his or her listening habits, high vs low SPLs.  If Wilson use a Gundry Dip, I don't find evidence for it on the net.

Vocal sibilance can vary on pressing.

I hear differences on a period press vs greatest hits vs 2nd press vs later reissues.

Example- Donovan's 1968  Hurdy Gurdy  Man-title track perfect on my stereo and mono press. NOT implying a new reissue is inferior-that's another thread to argue about.

Hurdy Gurdy Man on the 1969 Greatest Hits-sibilance. 
"came ssssinging  ssssongssss of love"

"tizzy" high hats on drumming tracks drive my crazy too!

Here’s the the thing about sibilance: it’s human.  It’s a natural sound of the human voice for certain words.  You can’t even say “sibilance” without a bit of sibilance.  In the very old days they were trying to design mics that WOULD pick up vocal sibilance, because not having it sounds crazy weird.  It’s actually the unnatural version of sibilance that bugs all of us.  But when we ask “is it on the recording?” and determine that it’s on the CD, it’s on the streaming file, etc., sometimes we falsely assure ourselves.  Patricia Barber’s Nightclub LP was well done, and so was the DSD file I own.  When my cartridge isn’t right (usually VTA), I can hear unnatural, spitty sibilance on certain tracks.  Is it on the DSD version?  Yes, but not to an unnatural degree.  Not spitting at me.  So, it’s not an “is it there?” question, it’s a “is the sibilance correct or not?” question.  On one hand, this will help avoid falsely concluding “it’s just on the recording.”  On the other hand, it also will help avoid concluding “wait, now I hear it on everything.”  My two cents: listen for unnatural sibilance, and fix it.  But if you start listening for ANY sibilance, you’ll find it everywhere.  And you will gradually feel yourself losing your mind.  Trust me.  This will be obvious to many A-goners, but I’m sure there are a few like me who could be twisting themselves in knots hearing sibilance everywhere, and I suggest you give yourself a break and instead listen for INCORRECT, overly noticeable, non-human sibilance. 
Next maddening topic: does it sound like a real cymbal tap, or just a pulse of white noise?  

Ding ding ding winner winner chicken dinner!  

Beautiful answer! This is what I was getting at above. Sibilance in and of itself is neutral and nothing to be battling with. Get your cymbals to ring and ting like actual cymbals and you will find your sibilance "problem" magically solved in the bargain.

Cymbals… really good point. I struggled with the sound of cymbals for years. I kept finding that the ting… and following ring was mostly distortion, and that when I got to a certain level suddenly they started sounding like brass… a very different sound. (I am not contradicting Millercarbon, but digging into the point from my perspective). I found that I had listened to so many concerts (amplified) and stereos that had treble actually being high frequency noise that mimicked the sound of cymbals, bells, tambourines, etc. I actually though that was accurate sound reproduction. So each time I made a change that improved treble it got quieter and less pronounced… but it also took on the rich multifrequency tone with the true harmonics of brass. I had to go out and listen to unamplified cymbals to be sure that my system wasn’t just tilted too far to the warm side. Anyway, back to sibilants, I think that is right, if you have cymbals sounding like brass then the sibilants will take care of themselves.