My battle with sibilance.

@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. 

@mijostyn """ : a mild dip at those frequencies. """, yes because it’s where the crossover frequency belongs , JA stated it.


"" . a very common approach to making certain program sources more listenable. ""

approach by whom because we are not talking about recording proccess but in specific about speakers and I took Wilson because you named but the speaker design behavior that you support and through almost any of the several JA speakers measurements just don’t confirm what you said but only confirm that your take does not exist.

""" The Maxx 2’s are a totally different speaker and they were not measured near field individually. """

you just don’t read it, here again. Btw, we are not reviewing the speaker only the " gundry dip ", that’s all:

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

Here a way different speaker that again confirm you have , at least, a misunderstood about:

https://www.stereophile.com/content/sonus-faber-venere-25-loudspeaker-measurements


I can show you 10 other different speaker measurements but at this time will be futile.


R.

mijostyn : The posted speakers measurements choosed were " contemporary " . Here an ADS vintage monitor from the late 70's- early 80’s. You can go to the last page ( 8 ) to read some measurements.

http://sportsbil.com/ads/l-2030-brochure.pdf

R.

@rauliruegas , somehow I think we are dealing with a language barrier/misunderstanding problem. 
Speaker measurements vary dramatically. The same speaker will measure very differently in different situations. The only measurement that is really valid is nearfield in an anechoic chamber. Very rarely if ever is this the case with speaker reviews.

Speaker designers can vary the presentation of a speaker in numerous ways by intension  manipulating a lot of factors and sometimes, to get what they are looking for requires a lot of electronics. The crossovers of the Dahlquist DQ 10 and the Apogee Diva's are great examples. What they had in mind is rarely known by the public. Some designers leave it up to the owner by giving them controls to adjust the relative driver volume or in my situation the contribution of one transformer vs the other transformer. Do any of them purposely boost bass and/or treble? You bet!
Most companies only want to sell loudspeakers and they do so but giving the public what they want and many will go for the speaker that is brightest or has the most bass. Companies will generally do anything to sell speakers. Those of us that buy expensive speakers are generally more critical and the companies that make them are more careful to keep the speaker as flat as possible in the average room. Who has an average room? What is an average room? 

Dropping the volume between 3 and 4 kHz is a well known way to diminish sibilance and there are many people who like an easy going loudspeaker that does not make them squint. Boosting bass and treble a little achieves the exact same result which is an easy going loudspeaker that sounds better at the lower volumes most people listen at.
My system is adjusted for playback at 95 dB. At 85 dB without loudness compensation it sounds a bit dull and bass light and people will notice this until I turn the volume up (or kick in the loudness compensation)
 
Because my front end is digital and managed by an advanced processor I can alter the frequency response +- 30 dB at any frequency from 0 Hz to 20 kHz either individually or as a group. Over the years I have experimented with hundreds if not thousands of curves which is why I can look at a frequency response curve and have a good idea what a system will sound like. I adjust my system to get the tonal balance and imaging I like. I have one preset loaded with my favorite curve but with a broad dip centered on the 3 to 4 Hz region for the occasional recording that gets sibilant at the volume I like which is why I and anyone who listens to my system know darn well that this works. 

As for what any speaker manufacturer had in mind? I have no idea. You would have to ask them. 

Dear  @mijostyn : I understand all what you said and yes no one of us can be sure what reviewers or speaker manufactured really do it but at least we can " work " with the " evidence " they show that we have on hand because  like it or not are the only " facts " we have around other than each one of us personal experiences.

You named Wilson and if you or any one else try to find out directly from Wilson the precise frequencies in the crossover of each of their models just you can get it, no information about.

Now, you have not evidence true evidence facts on the sibilance issue, what you posted till today has no evidence shows no single facts.

Yes, you are sharing your experiences and what is functioning for you what meet your MUSIC/sound priorities. That's all.

Fortunatelly I don't have sibilance true problems in my room/system so your " gundry dip " is useless for me.

I wish you really show clear and precise facts not coming for you but from other " sources ". In the mean time as I told you we all should " works " with the facts that comes from manufacturers and reviewers. I'm speaking of facts.

You show through your posts the different problems you have with your room/system and how you are fixing it. Thank's for that. Always is time to learn and I learned through this thread.

Regards and enjoy the MUSIC NOT DISTORTIONS,
R.