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Multi-Way Conventional loudspeakers with crossovers

BBC Dip
BBC Dip
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Old 27th August 2015, 02:15 AM   #21
system7 is offline system7  United Kingdom
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Quote:
Originally Posted by sreten View Post
Hi,

Well good look with that. You don't seem to understand the problem (Fast factorisation of the product of two primes).
If it was easy cryptography would be fatally fundamentally flawed.
There is no efficient "crack" to the problem, that is the point.

rgds, sreten.
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:

Quote:
Originally Posted by fishball79 View Post
You can see for yourself in Stereophile's measurements of their reccomended 2.5 or 3 way speakers for 2014. The common trend I see is a dip ~100hz to 1khz except for the YG Acoustics.

Vivid G1 Giya Metal Dome Tweeter
Click the image to open in full size.

Wilson Audio Alexandria XLF Soft Dome
Click the image to open in full size.

YG Acoustics Sonja 1.3 Waveguide dome
Click the image to open in full size.

Joseph Audio Perspective SEAS Excel Soft Dome
Click the image to open in full size.

Sonus Faber Venere 2.5 Waveguide Soft Dome
Click the image to open in full size.

Revel Performa3 F208 Waveguide Ring Radiator
Click the image to open in full size.

Goldenear Aon2 Cylindrical Planar Tweeter
Click the image to open in full size.
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:

Quote:
Originally Posted by John Atkinson
The Josephs and Rogerses have more top-octave energy apparent than the sweeter-toned Vivids, though the G3s and Perspectives have similar midrange outputs. But note how the Perspectives output 2–3dB more presence-region energy than either of the other two speakers, which are virtually identical between 2 and 10kHz. Here, I believe, is why Erick Lichte found the Perspectives not to work optimally in his room, which is smaller than mine, and why I found the Josephs to be unforgiving of poor-quality recordings and fussy about choice of amplifier. The presence region is where the ear is most sensitive—even a slight emphasis in this region can significantly affect the listening experience.
So is Earl right?
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Old 27th August 2015, 02:40 AM   #22
rayma is offline rayma  United States
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Originally Posted by infinia View Post
It's probably just another Myth still making the rounds via the internets.
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.

Last edited by rayma; 27th August 2015 at 02:42 AM.
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Old 27th August 2015, 02:48 AM   #23
infinia is offline infinia  United States
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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
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Last edited by infinia; 27th August 2015 at 03:18 AM.
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Old 27th August 2015, 03:10 AM   #24
Bigun is offline Bigun  Canada
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BBC Dip
so, is a BBC dip a desirable feature these days ?
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Old 27th August 2015, 04:48 AM   #25
ScottG is offline ScottG  United States
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Originally Posted by infinia View Post
My father, Dick Gundry,
..and here I thought it was Keith. My bad.
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Old 27th August 2015, 05:10 AM   #26
ScottG is offline ScottG  United States
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Originally Posted by Bigun View Post
so, is a BBC dip a desirable feature these days ?
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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Last edited by ScottG; 27th August 2015 at 05:24 AM.
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Old 27th August 2015, 07:12 AM   #27
Mooly is offline Mooly  United Kingdom
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BBC Dip


OT posts removed and points issued. Those posts that remain, you argue out on technical merit not by trading insults.
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Old 27th August 2015, 07:16 AM   #28
Zuhl is offline Zuhl  England
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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.
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Old 27th August 2015, 11:34 AM   #29
5th element is offline 5th element  United Kingdom
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Quote:
Originally Posted by Zuhl View Post
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.
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.
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Old 27th August 2015, 12:25 PM   #30
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No Dip, no sell..
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