Teo_audio wrote: " I find that the most natural and comfortable to listen to speakers are the ones that employ some subtle version of "The BBC Dip"."
Agreed - a bit of dippage centered somewhere between 3 and 4 kHz does seem to correlate with long-term fatigue-free listening.
One way of seeing the BBC Dip is "inverting the Fletcher-Munson peak", as atdavid so eloquently described it.
But here’s another way of seeing it: The BBC dip is right smack where the bottom end of most tweeters is, where most tweeters have an off-axis pattern flare. The result is a net excess of energy in this region (the off-axis energy perceptually adds to the on-axis energy), and the BBC dip is one way of addressing that.
One day I was curious about whether the BBC dip would be subjectively desirable if there were no off-axis energy flare to compensate for. My designs are constant-directivity over much of the spectrum including that region, so I dialed in some gentle dippage centered between 3 and 4 kHz. What I heard was educational to me.
Yes the speaker became more forgiving, but the harmonic richness was degraded. There was something obviously missing relative to having smooth response through that region. The loss of something quite desirable - timbre and texture and a natural-sounding richness - caught me by surprise.
So while the BBC dip does invert the Fletcher-Munson peak, I have come to believe that its primary raisin d’etre is to compensate for that off-axis energy flare at the bottom end of the tweeter’s range. And if that flare isn’t there, ime the BBC dip would be a step in the wrong direction.
One thing that peak in the Fletcher-Munson curve DOES tell us, in my opinion, is where the stakes are the highest.
Duke
