I do understand the problem. Even spent a few weeks on it. Takes you deep into prime number theory. Interesting notions that the square of a large prime is always of the form 24n+1. Large primes are always of the form 6n+1 or 6n-1. And we now have elliptic curves, which are powerful.
But most of the top people work for the various spy centres, and if they've already cracked it, they won't tell.
But for all that, it might be an INTERESTING waste of time. Like any hobby.
Onto the main thrust, and I've checked the tweeters:
I just thought I'd run up Earl Geddes' notion that wide dispersion needs a BBC dip/slope on these flagship speakers.
The one that bucks that trend is the Joseph Audio Perspective, but it sounds bright:
John Atkinson said:
So is Earl right?
From: Harbeth UK - High quality loudspeakers made in England
I've heard mention of 'the BBC dip' or 'the Gundry dip'. What does that mean?
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.
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^ according his son, has another story not as intriguing as above. Sean Olive never heard of the 'BBC dip' until 2009 LOL
Harbeth makes a good story tho > legends sell more or as PeeWee Herman said " I meant to do that"
link 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
Harbeth makes a good story tho > legends sell more or as PeeWee Herman said " I meant to do that"
link 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
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Member
Joined 2009
Paid Member
Perceptually, possibly.
reason 1:
There is that point with a given design where the polar pattern changes from largely omni to forward emphasis (..infinite baffle's excluded). The perceptual effect often moves images closer to the speakers and to each other - "bunching things up". It's not a natural effect for reproduction, so perhaps a little shelving somewhere in that 1-3.5 kHz region is useful to correct this problem.
reason 2:
There is evidence to suggest that our hearing is a bit too acute in the 1.5-5 kHz region, at least for stereo productions and reproduction of them in standard stereo. We tend to locate actual sources (tweeters) to the detriment of realism. Because it's largely an issue of intensity at these freq.s directly impacting location, I suspect it's an intensity gradient condition - you hear the pressure loss with distance and "track" back to the source automatically. Lower the pressure in that region relative to the average and you should diminish the effect - placing greater emphasis at a lower passband). (..another solution is using a diffusor or some sort of blocking mechanism to lower the amount of direct sound reaching the ear in that passband.)
-it is of course something worth experimenting for your own personal use.
Oh,
reason 3:
An impedance reaction causing an emphasis in pressure in this region, with a moderately high output impedance from the amp. and the typical rise in impedance at a typical crossover near 2 kHz. Amp dependent of course. Here you are basically trying to get back to "flat" in this passband, not have a net dip in response.
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Bextrene coned drivers have an upper mid colouration, even when doped; this and the poor dispersion of 8" drivers can lead to an unpleasant listening experience.
Good drivers with a flat response will always make a speaker sound better than poor drivers with any 'dips' and 'bumps'. It's better to fix the problem than fudge it.
Good drivers with a flat response will always make a speaker sound better than poor drivers with any 'dips' and 'bumps'. It's better to fix the problem than fudge it.
Well the problem that's being fixed here is the overly forward and aggressive sounding aspect of speakers with a wide narrow wide dispersion pattern within the 1-3kHz range. Having hyperacusis I can say that this makes my ears hurt. To others it simply sounds like the loudspeakers have a pronounced presence region. Good waveguide designs, by comparison, sound relaxed and unfatiguing.
Hi,
Your taking nonsense. The HF peak was in a "BBC rise" thread
and its true, the top end was exaggerated intended to pick up
16KHz line sweep breakthrough on TV audio channels.
In the same thread I defined the "BBC dip" as something
else. The same definition as I stated earlier in this thread.
rgds, sreten.
Sreten who is talking rubbish? youre just continually adding spin on some ad copy or reviews selling some speakers which may or more likely may not resemble the sonic characteristics of one or two designs produced in small quantities many decades ago.
You've added zero facts to the discussion, you haven't proved there is such thing BBC rise. IMO pointing at a review showing flat response and messaging the results with words from someone whose never measured a speaker, doesn't make it so.
*I have NOT seen one measurement, Xover simulation, test procedure or schematic provided by you to document or support the so called BBC dip either. BTW If you want to define something at least divulge any sources. even a entry to a wiki article requires that , sorry just repeating stuff you heard somewhere doesn't make facts. Sreten when pushed before you said what your authority was to define it ( nonsense indeed),
You've added zero facts to the discussion, you haven't proved there is such thing BBC rise. IMO pointing at a review showing flat response and messaging the results with words from someone whose never measured a speaker, doesn't make it so.
*I have NOT seen one measurement, Xover simulation, test procedure or schematic provided by you to document or support the so called BBC dip either. BTW If you want to define something at least divulge any sources. even a entry to a wiki article requires that , sorry just repeating stuff you heard somewhere doesn't make facts. Sreten when pushed before you said what your authority was to define it ( nonsense indeed),
Hi,
God, you like being tedious. I don't need to prove anything.
Take it on board or ignore it, its up to you. The BBC "dip" and
"rise" maybe myth. I'm just saying what they allegedly were,
as far as I can recollect, from the time they were terms used.
rgds, sreten.
First time i measured a pair of B&W speakers, I found out that my ears did not deceive me as much as I thought. B&W speakers - I experienced later - generally has a broad dip in the upper midrange and lower tweeter region. Dont get me wrong, most B&W speakers sounds fine, but IMHO they simply lack the detail in that region, which I really like. And in my current active setup, I simply go for a near straight line with an even dispersion in this region and it sounds wonderfull and full of all these small details that I personally like. I know that some bad produced music will suffer a little, but hey, theres alot of music out there. So i simply find something else to listen to.
Very interesting
The curves shown do not give a clear dip in the area described as the BBC presence of 'Gundry dip, and there is a quote of a dip between 100Hz and 1kHz which is in a very different part of the spectrum.
I'm also surprised at the response shown of the Goldenear speaker, rather poor IMO, and someone I recently met online sold his ADAM Tensor Betas to buy Goldenear speakers, which surprised me.
The issue of 'dip or not is moot, and seemingly now viewed as rather more to do with the nature of the ear and it sensitivity to indirect sound being different from that of direct sound, rather than a 'cover-up' of the design problems around Xover.
Surely any correction because of the above should be done by in the recording process with flat speakers, and imbued into the recording so that we at home can hear that on our flat speakers. Of course this requires similar room acoustics.
I also came across another very good discussion on this on Parts Express.
Any new info/discoveries on this topic since the last post?
The curves shown do not give a clear dip in the area described as the BBC presence of 'Gundry dip, and there is a quote of a dip between 100Hz and 1kHz which is in a very different part of the spectrum.
I'm also surprised at the response shown of the Goldenear speaker, rather poor IMO, and someone I recently met online sold his ADAM Tensor Betas to buy Goldenear speakers, which surprised me.
The issue of 'dip or not is moot, and seemingly now viewed as rather more to do with the nature of the ear and it sensitivity to indirect sound being different from that of direct sound, rather than a 'cover-up' of the design problems around Xover.
Surely any correction because of the above should be done by in the recording process with flat speakers, and imbued into the recording so that we at home can hear that on our flat speakers. Of course this requires similar room acoustics.
I also came across another very good discussion on this on Parts Express.
Any new info/discoveries on this topic since the last post?
As an objectivist I seek accuracy rather then what 'sounds nice', and I am currently worried that my recent purchase of very expensive loudspeakers resulting from a successful litigation, are lacking in presence, mainly at the lower end of that 1 to 3k band. Very often voices are recessed, but not always, and the range of that is very wide.
I've looked at this aspect of the BBC dip for a long time and wondered, it seems apparent that it may well have been done by them to ameliorate the Xover and dispersion problems, but never-the-less a 'bodge' solution.
Is it possible to get to the bottom of this, or is it just another part of Toole's "circle of confusion"?
If by "bump" you mean a boost, surely that would make matters worse rather than better.
My own recent build has a very simple 4th order L/R filter with no attempt at any alteration, and sounds OK. (With ESS Heil)
Alan Shaw of Harbeth states his intention as flat, and his speakers are regarded as smooth. So, what is going on?
I've looked at this aspect of the BBC dip for a long time and wondered, it seems apparent that it may well have been done by them to ameliorate the Xover and dispersion problems, but never-the-less a 'bodge' solution.
Is it possible to get to the bottom of this, or is it just another part of Toole's "circle of confusion"?
If by "bump" you mean a boost, surely that would make matters worse rather than better.
My own recent build has a very simple 4th order L/R filter with no attempt at any alteration, and sounds OK. (With ESS Heil)
Alan Shaw of Harbeth states his intention as flat, and his speakers are regarded as smooth. So, what is going on?
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