My battle with sibilance.

@lewm , the dip is there. Now, you could argue as to whether or not it was intentional. Would Wilson do something that was not intentional? 
Most loudness controls I am familiar with are just on/off switches with only one curve. It would be very complicated and expensive to rig an analog variable control. My TacT is the only unit I know of that has dynamic loudness compensation. It hops from one curved to the next with output level. It happens automatically. I love it. But, no other digital preamp with the power do do this has the programming. I suspect (but do not know for a fact) that Bozevick had a patent or copywrite on this programming. Others will institute it in time. 
By the way, there is no one Fletchur-Munson curve. It is a continuum that is outlined by a set of curves that vary with sound pressure levels. Your ears do not hop from one curve to the next.

Most loudness controls on old school preamplifiers and receivers were continuously variable, sort of like bass and treble attenuators combined into one circuit.  So, for example, if you rotated them to left of center, you got a reduction in compensation for the Fletcher-Munson curve.  If you rotated them to the right of center, you got enhanced compensation.  Center detente could be the off position.  (I am not claiming that every Loudness control operated exactly like this; just giving an example.) This allowed for variable correction based on the SPLs at the listening seat.  You see such controls on Japanese equipment right up to this century.  40-50 years ago they were standard on some Harmon Kardon, Marantz, Fisher, Sherwood, etc. gear.  Would you agree that that would be better than one fixed Gundry dip built into a crossover?  Further, the complex network required in the speaker crossover to effect the Gundry dip would require inductors and capacitors, bound to muddy up the SQ.  Let's see, when you personally measured a Wilson speaker, was it in an anechoic chamber?  Could you rule out room effects to help produce the dip you may have observed?  But easiest of all, ask Wilson. I strongly doubt they would introduce such a complex network into their crossovers; it's tough enough to build a linear and transparent crossover network successfully, especially for the 3-, 4- and 5-way speakers built by Wilson.

    Ok, I dug up the Men From Down Under (Business As Usual, US Columbia print) and washed and vacuumed them throughly, and still they were working...at jackhammering my AT540ml cart in the air on the opening cut.  Not the Men's fault; deformed lip and mold, etc.
   Further tracks in, no vocal sibilance (but very close), the cymbals decay though just blended together. Played @ about 70-80Db.  Fluance RT85 with the upgraded cart, Mani phono pre, Pioneer Elite 803 in 2ch, Vandersteen 2ci, HSU sub.
  Had to quit before taking RickyLee for a spin cause the cat came up from the basement to complain. (anything over -30db amp and he's gone)  And I'm usually more dancing to "Danny's All Star Juke Joint" than critical listening anyway.
  My own recent sibilance annoyance came with Magro Timmons' voice on the highly regarded "Trinity Session"...CD. It's the only example I've noticed on my headphone separate system: Arya, Jot2, Bifrost2, Oppo85. Need to rip it and see if usb input "cures" it.  No cat issues!

Dear @mijostyn @lewm : "" Some speaker manufacturers, to make their speakers sound better at low volumes and reduce sibilance tuned their speakers with a built in Gundry dip. Wilson did this with the Watt/Puppy. ""

Low volumes, Gundry dip and Wilson speakers? well maybe you think you are rigth but unfortunatelly you are wrong and with out evidence about your statement.

First mistake that never existed or exist that ( ? ) Gundry dip :


"" Well, of course having found this, I have to jump in. My father, Dick Gundry, who spent almost all his working life in the BBC and was for many years responsible for maintaining technical standards in BBC Radio (which have sadly gone down since his retirement in about 1971), and who was known behind his back as golden ears, would not have been pleased to have his name attached to a deliberate departure from a flat frequency response in loudspeakers. Has anyone any idea on how this term arose? It must have been much more recent than 1971.

One of my father’s responsibilities back in the late 1950s and early 1960s was the development of stereo techniques in preparation for a means to broadcast it. ...............the uniformity was considered more important than perfect flatness, and thus the speakers may have shown the "Gundry dip". However it would not have been a design aim but a side-effect, and in any case my father would have had no input to the designs...

Kenneth Gundry, San Francisco ""




In 2009/2010 we can read these statements by a true expert:


"" Neither I nor Floyd Toole had never heard about the Gundry dip until about 2 months ago when an audio reviewer used the term in an email to us. Many poorly designed 2-way loudspeakers already have dips in the sound power response in the cross-over range 1-3 kHz where the directivity of the woofer is too high compare to the directivity of the tweeter at those frequencies. As a result, this produces a notch in the sound power response of the loudspeaker, usually followed by a peak. Depending on the bandwidth and depth of the notch, it is the peak that is often heard as sounding objectionable (harshness, hardness or excessive brightness). The extent to which this a problem depends on whether you are sitting on or off axis, and the reflectivity of the room.

To some degree, Harmon/Sean Olive’s research strongly asserts that listeners will universally prefer a flat frequency response under blind listening conditions. That alone is a pretty good reason. ""

S.Olive has several papers in the AES when he made it a lot of speakers research at Harmon, including why we need several subwoofers in a home audio systems but in this research ( white papers ) stated that 2 subs are ok at one seat position.



More information for the ones that really know about:


""" There is much myth, folklore and misunderstanding about this subject.

The ’BBC dip’ is (was) a shallow shelf-down in the acoustic output of some BBC-designed speaker system of the 1960s-1980s in the 1kHz to 4kHz region. The LS3/5a does not have this effect, neither in the 15 ohm nor 11 ohm, both of which are in fact slightly lifted in that region.

According to Harbeth’s founder, who worked at the BBC during the time that this psychoacoustic effect was being explored, the primary benefit this little dip gave was in masking of defects in the early plastic cone drive units available in the 1960’s. A spin-off benefit was that it appeared to move the sound stage backwards away from the studio manager who was sitting rather closer to the speakers in the cramped control room than he would ideally wish for. (See also Designer’s Notebook Chapter 7). The depth of this depression was set by ’over-equalisation’ in the crossover by about 3dB or so, which is an extreme amount for general home listening. We have never applied this selective dip but have taken care to carefully contour the response right across the frequency spectrum for a correctly balanced sound. Although as numbers, 1kHz and 4kHz sound almost adjacent in an audio spectrum of 20Hz to 20kHz, the way we perceive energy changes at 1kHz or 4kHz has a very different psychoacoustic effect: lifting the 1kHz region adds presence (this is used to good effect in the LS3/5a) to the sound, but the 4kHz region adds ’bite’ - a cutting incisiveness which if over-done is very unpleasant and irritating. """"


Wilson speakers?:

https://www.stereophile.com/content/wilson-audio-specialties-wattpuppy-system-8-loudspeaker-measurem...

John Atkinson has a lot of solid experiences about making " hundred’s " of speaker measurements ( in room and anechoic. ) and you can read in the Watt measurements this JA statement:


" The Wilson speaker’s lateral-dispersion plot (fig.7) indicates a broadly even radiation pattern, with an off-axis notch developing around 4kHz, where the on-axis response has a small peak. In the vertical plane (fig.8), the treble region doesn’t change much for listening axes on or just below the tweeter. However, a large suckout develops at 3.3kHz above the tweeter axis, which I assume is the frequency at which the WATT’s tweeter crosses over to its woofer. ""

Here another Wilson measurements:

https://www.stereophile.com/content/wilson-audio-specialties-maxx2-loudspeaker-more-measurements

JA: """ but the most obvious difference between the speaker’s balance in the two rooms is that the MAXX 2s produce an impressively flat midrange and treble at Paul’s considerably greater listening distance...."""


Take a look of your " Gundry dip " in this speaker measurements:

https://www.stereophile.com/content/dynaudio-evidence-master-loudspeaker-measurements

D.Wilson before designed the Watt was some years a recording/producer engineer.
The Watt does not came at " random " but because the high knowledge levels of what are the needs for a speaker recording studio monitoring.

I could think that you own the recordings under D.Wilson label. Well the speaker monitoring ( in location ) was the Watt and the WAMM at Wilson Audio. Great recordings and a must to listen it in the rigth room audio system.

mijostyn you have to make more research about. There is a lot of expert information in the internet.

Yes, lewm is rigth just from the begining and as he I never heard before about that Gundry myth. Now I learned why.


R.

@rauliruegas, putting a 2-3 dB notch filter between 3 and 4 kHz is a very common approach to making certain program sources more listenable.
I suggest you take a very sibilant recording and try it. It is rather cool to hear the sibilance disappear (along with a little detail). How it got it's name as the "BBC" or "Gundry" curve doesn't really matter. I use those terms because that is what the industry seems to want to call it. I did not make it up. 

As for Watt/Puppies, measured at one meter with modern computerized equipment they demonstrate a mild dip at those frequencies. I am absolutely sure those measurements were done correctly. The Maxx 2's are a totally different speaker and they were not measured near field individually.  I have heard but have no proof that other manufacturers have done this. That graph, by the way has very poor resolution, is crude and you should note the measurement indicates a +- 2.5 dB variance throughout most of the midrange which the writer is calling "impressively flat." For an uncorrected speaker it is impressively flat but the bass is not good. It is down at 150 Hz, up at 80 Hz and falls off steeply below 50 Hz.
In order to get realistic low bass at reasonable levels the bass has to rise as you go down from 100 Hz. I adjust my system to be up 5 dB at 20 Hz.
The dip at 150 Hz is going to rob the bass of detail and impact. Pipe Organs can go down to 8 Hz. 16 Hz is no problem (but an extremely large pipe) The Maxx's bass response is, at least in part due to room nodes. 

Very occasionally I will use the notch filter. I dislike loosing detail and you can frequently cut the sibilance by just turning down the volume a bit.