I've been aware for a while that many loudspeakers intentionally reduce the "harshness" range around 2 to 4 KHz to sound smoother and less fatiguing. I've seen data for speakers having dips as large as 8 dB!
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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.
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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. (Some of those early experimental recordings have more recently been issued on CD by the BBC). At that time the BBC developed its own monitoring loudspeakers on the grounds that commercially available ones were generally not very good. I used to say that loudspeakers were either good or loud but not both! During early stereo experiments it became apparent that the best BBC monitoring speakers of the day did not perform well in pairs for stereo because they did not match each other closely enough, particularly in phase response, so central images tended to be diffuse. A major reason was that to accommodate variations in the drivers each and every cross-over network was adjusted for a flat amplitude response. A new range of speakers was developed, but it is possible that at least for those first ones, 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, which were developed at the BBC Research Department (Dudley Harwood, Spencer Hughes et al.)
Kenneth Gundry, San Francisco
https://hydrogenaud.io/index.php/topic,75195.0.html
Exponering under längre tid för ljud kring 85 dB och lite däröver ger hörselskador enligt figuren nedom. Hörselskadan börjar vanligen med ljudöverkänslighet och efter ca 10 år kommer allt mer tinnitus i skadat frekvensområde. Ljudöverkänsligheten är vanligen kring 3500 Hz dvs området där vi är som känsligast. Många förstår inte att de har en ljudöverkänslighet.
Musiker och även klassiska musiker är överrepresenterade i gruppen ljudöverkänsliga.
BBC gänget hade sannolikt exponerats för ljud på 85 dB och där över under många år.
https://www.av.se/globalassets/filer/pu ... 2013-2.pdf
Så sannolikt är BBC-dippen en kompensation för ljudöverkänslighet. Med dippen lät stereo bättre.
Efter vad jag förstår har flera på detta forum utvecklat tinnitus och borde tidigare varit ljudöverkänsliga.
Känner någon igen att ljudet med åren blivit mer njutbart med allt mer BBC-dipp.
JM
) ersätts då av en korrektion som håller sig inom +/- 0,8 dB. Därtill kan det vara aktuellt att addera några ytterligare småkorrektioner för att erhålla en så klangligt neutral/ackurat klangtergivning som möjligt, men det är en annan historia. 
Kanske är det mindre lämpligt att uppmana sina forumkamrater att studera.