Folks,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! I really hate that, especially in speakers sold to the pro audio market. If everyone mixes on speakers like that, those of us who care about accuracy and have flat speakers will have more harshness than usual. Plus, it's dishonest.Anyway, I learned the other day that this "dirty little secret" of the speaker industry actually has a name - the Gundry Dip, also called the BBC Dip apparently related to some early BBC research.I'm trying to learn more about the origin of this intentional dip, but all I get from Google is links to people discussing it in audio forums. I'm trying to find something more authoritative. Does anyone know where I can read more about this?--Ethan
I can certainly understand that you wouldn't want this sort of thing in a control room.
Unless the speakers are specifically advertised as not having this dip how is it in any way dishonest?
Quote from: analog scott on 23 October, 2009, 12:13:31 PMI can certainly understand that you wouldn't want this sort of thing in a control room.Right, and that's my main concern.QuoteUnless the speakers are specifically advertised as not having this dip how is it in any way dishonest?There's the rub. Have you ever seen a speaker vendor admit their speakers are intentionally skewed to sound "better?"--Ethan
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.Pretty good reason for what?Beyond that, as far as individual preferences are concerned, the adjustment of preferences via a change in speakers seems less preferrable than getting a speaker with the flattest response and then applying eq. I'd imagine that the latter approach will generally yield a final response that is less ragged and lower Q in nature, although I don't have any real evidence to back that up.
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. Some room correction products, by default, have a dip in their target curve in an attempt to compensate for this sound power problem, essentially trying to second guess whether or not the loudspeaker is well-designed. As I've shown in a recent AES paper - this doesn't always lead to good results.
You can see this notch/peak in the BBC frequency graphs of the LS3. I also wonder, if people are not hearing distortion when these small loudspeakers are overdriven.CheersSean
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.
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.You can explore this effect for yourselves by routing your audio signal through a graphic equaliser and applying a mild cut in the approx. 1kHz to 4kHz region and a gradual return to flat either side of that.