Almost impossible I would say, hence, IMO, the futility of showing and to a certain extent attending. I would certainly never jusge a good speaker from a show. The dogs become kind of obvious and would most likely be dogs in any setting, but maybe to a differing degree. One can examine new technology by just looking at it in many cases (and then there is the fun of listening to the snake-oil sailman trying to sell cables.)
Yes, my impression as well. Very smooth frequency response, not colored at all (DSP I suspect), but no maging at all - just infiite space with instruments "somewhere".
Sounds like a dream come true for the concert hall crowd. I wonder if this requires spending that kind of money though.
Hi Guys
Regarding the loudspeakers “spatial identity”, I had some thoughts and recollections about this and wanted to expand on what Fast and Kindhornman have speculated.
If / when our ears are each presented with an identical signal from a forward position, that signal is effected by the shape of our ears and head BUT both L and R are effected equally and so we hear the height location due to those acoustic alterations (our ears and head impose depending on the sounds direction) but it sounds like it’s in front of us.
If you take away the angle dependent effects of your outer ear by using headphones (that present sound perpendicular to the eye / ear view), you have removed what tells you height etc. It is the effect your ears and head have (that we are all 100% unaware of), we can’t hear any of that consciously BUT those changes ARE part of what our brain uses to tell the spatial stuff
It is because of all those direction related head / ear changes, that one can put tiny microphones inside a persons ears and record (in the ear recordings) which when played back properly (minimizing the ear effects), one can make a hair raising real sounding recording (for one listener in one location).
I heard some recordings Don Davis made (old days Synaudcon), one, a recording made of a fellow walking around the pits at the Indy 500, really gave me goose bumps and I guess is partly why I am so interested in imaging and capture of a stereo image.
The first time I ever heard a speaker with little identity was in the 90’s at Intersonics when I was “fixing” (removing the protection) from my bosses esl-63’s. I built the levitation transducers and electronics and made ESS speakers for fun back then and my boss (to my horror) asked me to “fix” his (very expensive) speakers.
I explained the annoying spark gaps were there for a reason and while they were a bother, they did tell you something. Anyway, out they came and a few months later of louder sound, they needed to be re-built.
A hifi writer, Dan Sweeney said to me once back then and it stuck like a tack in my forehead “there are speakers that sound good, there are speakers that go loud, but none do both”.
Anyway, when I fired the first of Roys ESL’s back up in my listening room, that is when I was struck by the way some sound / recordings seemed to come from behind the speaker. It made me wonder why and I thought it had to be the way the speaker radiated, not how it worked.
In that case, the difference between the ones I was making and this was that the speaker was driven in concentric rings, starting at the center. The light went on, we made acoustic levitation systems at work and at 20KHz, the wavelength was about 5/8 inch.
A surface as large as the ESS speaker would be many wavelength across but by driving the rings sequentially, a segment of a spherical wave front was produced. You can see the ring constriction here;
http://www.audiodesignguide.com/esl/esl63ph.jpg
The signal for each ring is progressively delayed by using an all ladder style pass filter, each filter provides a small time delay. A model of that is here;
http://mark.rehorst.com/Quad_ESL-63/Quad ESL-63 Simulation Schematic.png
The result was that even though the source was large compared to the wavelength, it radiates as a partial sphere, “as if” the source really was behind the film and the sound wave simply traveled through it’s flat plane..
Fast forward about 15 years.
When I was really struck by this effect again was working on the early Unity Horns, as the TEF measurements showed they were getting closer and closer to one source in time and space, I kept hearing an increasing disconnect with the physical depth location. There wasn’t anything in particular I could see in the measurements but the effect was quite audible and puzzling.
later Synergy horns eliminated the crossover phase shift and the effect more pronounced. A friend, Doug Jones has been an acoustics researcher and professor and was department chair at Columbia college in Chicago and had worked with Gary Kendall in the old days on stereo imaging. Doug made the old LEDR stereo test recordings if any of you are that old.
He was the curator of the Heyser archive / library at Columbia and he allowed me to look around at Dick’s stuff and read some of his unpublished work. I met Dick once at a dinner with Don and Carolyn and a bunch of other audio types a year or two before he passed away but I only said a couple words he whole night lest I prove how I felt in their presence. Doug was a friend of his though and it was cool to hear more about him.
Anyway, for a year or so, about twice a month Doug and I were having breakfast and talking about sound, stereo etc and then coming back here to listen and to make a long story short he quit teaching came to work for us now. Doug condensed what I had observed and what he heard into a nugget of simplicity.
The idea I proposed was that to localize the depth location, one has to be getting sounds to the R and L ears that has “enough” difference for your brain to detect / triangulate the source location.
So Doug’s condensation was that a true simple spherical, plane and cylindrical wave would all have this effect because in each case what reaches the two ears is identical.
The inverse of this is that the more irregular the radiation pattern is, the more clues the radiation pattern carries about the source itself.
We can’t see this domain and while we can “hear” aspects of it, a visual example is better.
In one case if you consider “ loudness” on a 3d polar plot, one has an omni-directional simple point source which looks more like a Q ball and then, one can have a complex radiation pattern looking more like this;
http://www.worldoceans.com/pix/c_spa07.jpg
Understand, right now, this isn’t about the room or other possible speaker flaws, only how uniformly it radiates and how similar the R and L ears pressures are from the source alone.
In the past here, I have tried to describe this effect here and if one wanted to “hear” how the radiation pattern is audible, to put a small good full range driver in the middle of a large baffle. Yes the source has other serious limitations as a “faithful” source but because they radiate as a simple source over much of the band (radiate a hemisphere up to upper mids), they can have phenomenal imaging..
What causes the more “puffer fish” radiation?
Any time you have more than one source of sound, that is more than about 1/3 - 1/ 2 wavelength spacing from the other source. This might be a tweeter with a step in the baffle which re-radiates or edge diffraction, a driver in breakup or used too high for it’s size etc etc.
We have to remember too that while an acoustically small driver on a flat baffle looks like just that, it radiates as if it were a 180 degree horn, up to the point the source has directivity and subject to problems impedance discontinuities cause and reflections re-radiations and so on etc. The things in horns Earl has identified as higher order modes can have their origin in the same kinds of things as edge diffraction, discontinuities etc on a flat baffle except the angle isn't closed enough for the re-radiation to bounce off a second surface.
Any or all of these and more can produce multiple paths which add differently in a space as small as the distance between your R and L ears and THOSE differences let you hear / localize the physical depth of the source.
Without those origin clues, all one has are the remaining “clues” encoded in the recording which then (ideally) dominates your perception. Without those clues, your brain hears a compelling mono phantom & stereo image and not the R and L speakers where the sound originates physically.
Again, none of this has to do with the room or other speaker flaws, it is only an observation about how a loudspeaker radiates so far as it’s spatial identity.
Also, playing a recording, all that also depends on the recording microphone, it’s placement, use and every part of the chain up to the speaker.
What ever this part of the radiation effect is, it is audible in a generation loss recording or one sided capture. A dealer of ours in Europe made a camcorder video that captures what you hear firsthand with this effect.
Understand, these are not hifi speakers and our SM-80 is more a loud / lower cost cabinet than a refined one, yet with headphones you can still hear some of what you hear in person with the source identity thing.
Danley Sound Labs SM80 vs. d&b Q7 - YouTube
So, what would one need to do this?
Exactly what many have observed themselves, mostly, speakers that radiate as a simple source over a broad band.
These would be some kinds of Horns that cover a broad enough band as one source, acoustically small (point ) sources on simple unchanging surfaces like a large baffle / horns which extend out to the pattern loss frequency for that angle and dimension and so on.
A floor to ceiling line source using a ribbon or continuous full range driver, could also do it, a planar ess speaker can do it if you’re up close and it really is a planer source.
The problems here are that the line and planar source MUST be large compared to the lowest F, longest wavelength of concern and for an array to work like a continuous source they can’ be more than about ¼ wavelength apart at the highest frequency of concern.
A point source is automatically what results from a source too small to have directivity, the pressure freely radiating away is the 3d equivalent of a pebble tossed into a pond, governed by the pressure gradient and speed of sound. This is why a small full range driver has this effect, a 4 inch driver only starts to get directivity as a simple piston source when the radiator is more than about 1 wl in circumference (K=1).
In the room?
Pretend all your walls, floor and ceiling are mirrors and your loudspeakers are now bare light bulbs.
From your listening position, how many light bulb images do you see? Hard to count them all.
Each image is an equal angle reflection like sound can produce and ALL the reflections compete with the direct image even if they look nice. Now pretend one has a flashlight instead of bare bulb, now because of directivity, there are very many fewer images of the light bulb, even only two if it’s narrow enough.
Now with that in mind that a typical loudspeaker radiates like a bare bulb up to where it begins to have directivity and many reach the narrow flashlight pattern very high up in frequency. In the room, the higher the frequency the more like light a sound reflection behaves.
If you take an impulse or ETC measurement at the listening position, you can usually see the first few reflections as they arrive with progressively longer delays because of the longer and longer path lengths.
Directivity.
Directivity is inconvenient, it has the “what frequency“ question attached, it is wavelength and geometry dependant and that makes having it at a lower frequency a non-starter for the home and so “it is not important” to most mfrs.
That assertion aside, many can apparently “still hear” a difference when they use self cancelation to produce a figure 8 dipole pattern and suppress / eliminate most or much of the side radiation (which would normally reflect off the walls and harm the stereo image in the recording) in exchange for stronger but later and possibly scattered rear energy.
It is really cool people are talking and thinking about this stuff.
Our hobby is in a sad state, it needs some breakthroughs and for the most part, the “business” looks to me like it is selling what you can make and like most marketing, a dollar marketing the image of technology brings in more sales than a dollar spent on developing technology.
Best,
Tom Danley
Regarding the loudspeakers “spatial identity”, I had some thoughts and recollections about this and wanted to expand on what Fast and Kindhornman have speculated.
If / when our ears are each presented with an identical signal from a forward position, that signal is effected by the shape of our ears and head BUT both L and R are effected equally and so we hear the height location due to those acoustic alterations (our ears and head impose depending on the sounds direction) but it sounds like it’s in front of us.
If you take away the angle dependent effects of your outer ear by using headphones (that present sound perpendicular to the eye / ear view), you have removed what tells you height etc. It is the effect your ears and head have (that we are all 100% unaware of), we can’t hear any of that consciously BUT those changes ARE part of what our brain uses to tell the spatial stuff
It is because of all those direction related head / ear changes, that one can put tiny microphones inside a persons ears and record (in the ear recordings) which when played back properly (minimizing the ear effects), one can make a hair raising real sounding recording (for one listener in one location).
I heard some recordings Don Davis made (old days Synaudcon), one, a recording made of a fellow walking around the pits at the Indy 500, really gave me goose bumps and I guess is partly why I am so interested in imaging and capture of a stereo image.
The first time I ever heard a speaker with little identity was in the 90’s at Intersonics when I was “fixing” (removing the protection) from my bosses esl-63’s. I built the levitation transducers and electronics and made ESS speakers for fun back then and my boss (to my horror) asked me to “fix” his (very expensive) speakers.
I explained the annoying spark gaps were there for a reason and while they were a bother, they did tell you something. Anyway, out they came and a few months later of louder sound, they needed to be re-built.
A hifi writer, Dan Sweeney said to me once back then and it stuck like a tack in my forehead “there are speakers that sound good, there are speakers that go loud, but none do both”.
Anyway, when I fired the first of Roys ESL’s back up in my listening room, that is when I was struck by the way some sound / recordings seemed to come from behind the speaker. It made me wonder why and I thought it had to be the way the speaker radiated, not how it worked.
In that case, the difference between the ones I was making and this was that the speaker was driven in concentric rings, starting at the center. The light went on, we made acoustic levitation systems at work and at 20KHz, the wavelength was about 5/8 inch.
A surface as large as the ESS speaker would be many wavelength across but by driving the rings sequentially, a segment of a spherical wave front was produced. You can see the ring constriction here;
http://www.audiodesignguide.com/esl/esl63ph.jpg
The signal for each ring is progressively delayed by using an all ladder style pass filter, each filter provides a small time delay. A model of that is here;
http://mark.rehorst.com/Quad_ESL-63/Quad ESL-63 Simulation Schematic.png
The result was that even though the source was large compared to the wavelength, it radiates as a partial sphere, “as if” the source really was behind the film and the sound wave simply traveled through it’s flat plane..
Fast forward about 15 years.
When I was really struck by this effect again was working on the early Unity Horns, as the TEF measurements showed they were getting closer and closer to one source in time and space, I kept hearing an increasing disconnect with the physical depth location. There wasn’t anything in particular I could see in the measurements but the effect was quite audible and puzzling.
later Synergy horns eliminated the crossover phase shift and the effect more pronounced. A friend, Doug Jones has been an acoustics researcher and professor and was department chair at Columbia college in Chicago and had worked with Gary Kendall in the old days on stereo imaging. Doug made the old LEDR stereo test recordings if any of you are that old.
He was the curator of the Heyser archive / library at Columbia and he allowed me to look around at Dick’s stuff and read some of his unpublished work. I met Dick once at a dinner with Don and Carolyn and a bunch of other audio types a year or two before he passed away but I only said a couple words he whole night lest I prove how I felt in their presence. Doug was a friend of his though and it was cool to hear more about him.
Anyway, for a year or so, about twice a month Doug and I were having breakfast and talking about sound, stereo etc and then coming back here to listen and to make a long story short he quit teaching came to work for us now. Doug condensed what I had observed and what he heard into a nugget of simplicity.
The idea I proposed was that to localize the depth location, one has to be getting sounds to the R and L ears that has “enough” difference for your brain to detect / triangulate the source location.
So Doug’s condensation was that a true simple spherical, plane and cylindrical wave would all have this effect because in each case what reaches the two ears is identical.
The inverse of this is that the more irregular the radiation pattern is, the more clues the radiation pattern carries about the source itself.
We can’t see this domain and while we can “hear” aspects of it, a visual example is better.
In one case if you consider “ loudness” on a 3d polar plot, one has an omni-directional simple point source which looks more like a Q ball and then, one can have a complex radiation pattern looking more like this;
http://www.worldoceans.com/pix/c_spa07.jpg
Understand, right now, this isn’t about the room or other possible speaker flaws, only how uniformly it radiates and how similar the R and L ears pressures are from the source alone.
In the past here, I have tried to describe this effect here and if one wanted to “hear” how the radiation pattern is audible, to put a small good full range driver in the middle of a large baffle. Yes the source has other serious limitations as a “faithful” source but because they radiate as a simple source over much of the band (radiate a hemisphere up to upper mids), they can have phenomenal imaging..
What causes the more “puffer fish” radiation?
Any time you have more than one source of sound, that is more than about 1/3 - 1/ 2 wavelength spacing from the other source. This might be a tweeter with a step in the baffle which re-radiates or edge diffraction, a driver in breakup or used too high for it’s size etc etc.
We have to remember too that while an acoustically small driver on a flat baffle looks like just that, it radiates as if it were a 180 degree horn, up to the point the source has directivity and subject to problems impedance discontinuities cause and reflections re-radiations and so on etc. The things in horns Earl has identified as higher order modes can have their origin in the same kinds of things as edge diffraction, discontinuities etc on a flat baffle except the angle isn't closed enough for the re-radiation to bounce off a second surface.
Any or all of these and more can produce multiple paths which add differently in a space as small as the distance between your R and L ears and THOSE differences let you hear / localize the physical depth of the source.
Without those origin clues, all one has are the remaining “clues” encoded in the recording which then (ideally) dominates your perception. Without those clues, your brain hears a compelling mono phantom & stereo image and not the R and L speakers where the sound originates physically.
Again, none of this has to do with the room or other speaker flaws, it is only an observation about how a loudspeaker radiates so far as it’s spatial identity.
Also, playing a recording, all that also depends on the recording microphone, it’s placement, use and every part of the chain up to the speaker.
What ever this part of the radiation effect is, it is audible in a generation loss recording or one sided capture. A dealer of ours in Europe made a camcorder video that captures what you hear firsthand with this effect.
Understand, these are not hifi speakers and our SM-80 is more a loud / lower cost cabinet than a refined one, yet with headphones you can still hear some of what you hear in person with the source identity thing.
Danley Sound Labs SM80 vs. d&b Q7 - YouTube
So, what would one need to do this?
Exactly what many have observed themselves, mostly, speakers that radiate as a simple source over a broad band.
These would be some kinds of Horns that cover a broad enough band as one source, acoustically small (point ) sources on simple unchanging surfaces like a large baffle / horns which extend out to the pattern loss frequency for that angle and dimension and so on.
A floor to ceiling line source using a ribbon or continuous full range driver, could also do it, a planar ess speaker can do it if you’re up close and it really is a planer source.
The problems here are that the line and planar source MUST be large compared to the lowest F, longest wavelength of concern and for an array to work like a continuous source they can’ be more than about ¼ wavelength apart at the highest frequency of concern.
A point source is automatically what results from a source too small to have directivity, the pressure freely radiating away is the 3d equivalent of a pebble tossed into a pond, governed by the pressure gradient and speed of sound. This is why a small full range driver has this effect, a 4 inch driver only starts to get directivity as a simple piston source when the radiator is more than about 1 wl in circumference (K=1).
In the room?
Pretend all your walls, floor and ceiling are mirrors and your loudspeakers are now bare light bulbs.
From your listening position, how many light bulb images do you see? Hard to count them all.
Each image is an equal angle reflection like sound can produce and ALL the reflections compete with the direct image even if they look nice. Now pretend one has a flashlight instead of bare bulb, now because of directivity, there are very many fewer images of the light bulb, even only two if it’s narrow enough.
Now with that in mind that a typical loudspeaker radiates like a bare bulb up to where it begins to have directivity and many reach the narrow flashlight pattern very high up in frequency. In the room, the higher the frequency the more like light a sound reflection behaves.
If you take an impulse or ETC measurement at the listening position, you can usually see the first few reflections as they arrive with progressively longer delays because of the longer and longer path lengths.
Directivity.
Directivity is inconvenient, it has the “what frequency“ question attached, it is wavelength and geometry dependant and that makes having it at a lower frequency a non-starter for the home and so “it is not important” to most mfrs.
That assertion aside, many can apparently “still hear” a difference when they use self cancelation to produce a figure 8 dipole pattern and suppress / eliminate most or much of the side radiation (which would normally reflect off the walls and harm the stereo image in the recording) in exchange for stronger but later and possibly scattered rear energy.
It is really cool people are talking and thinking about this stuff.
Our hobby is in a sad state, it needs some breakthroughs and for the most part, the “business” looks to me like it is selling what you can make and like most marketing, a dollar marketing the image of technology brings in more sales than a dollar spent on developing technology.
Best,
Tom Danley
I listen mostly to classical music and I like big music. I've found after years of listening to live and recorded that the problem with the recorded sound is twofold: the speakers are often not competent (I've found that speakers such as Earl's or Tom's give the best experience); the room is problematic - the smaller it is, the more problems - and the best solution I've had is to increase the LF modal density with extra subs, kill early reflections, and run surrounds with delays and HF roll offs. That sort of gives the big room experience in a small room.
It's not ultimately satisfying but I think if surrounds could really give me more decorrelated sound it could be better.
When I get some more money I'll redo the experiment more rigorously with measurements.
Tom, great contribution.
Just two small additions. The smaller the wavelength, the more gets absorbed/scattered upon reflection. The frequencies that cause the most issues imo are those fairly low in the spectrum, where reflections create comb filtering.
The brain is very adept at filtering out room reflections that are perceived by two ears. In other words, your room may be filled with reflections, but the ear/brain systems knows how to give precedence to the direct sound. That's what it does for a living.
Just two small additions. The smaller the wavelength, the more gets absorbed/scattered upon reflection. The frequencies that cause the most issues imo are those fairly low in the spectrum, where reflections create comb filtering.
The brain is very adept at filtering out room reflections that are perceived by two ears. In other words, your room may be filled with reflections, but the ear/brain systems knows how to give precedence to the direct sound. That's what it does for a living.
The planar concentric ring source will deliver the smoothest radiation pattern by far. Tim Mellow and Leo Kärkkäinen have worked on this lately:
http://www.mellowacoustics.com/articles/Dipole_speaker_with_balanced_directivity.pdf
The point source on a large baffle is much worse:
http://www.mellowacoustics.com/articles/Disk_in_a_circular_baffle.pdf
This is the point source on a large baffle:
Rudolf
Tom,
I appreciate all the time you take to try and answer these rather difficult questions. I am working on a new speaker design for a consumer application and it is not a trivial exercise to do what we know needs to be done when we can't use waveguides due to size limitations. I do have the advantage that I will not have to use a wooden enclosure.
I am molding the enclosure in a high dollar material that has very good acoustical properties. I can shape the enclosure to take advantage of the material, but it is still a design conundrum when you are using two discrete devices, I can move diffraction from one plane into another but can not eliminate them in both the vertical and horizontal planes simultaneously without going with a coaxial design. A coaxial design brings in its own set of compromises that I don't think will outweigh the mechanical limitations of that solution.
The room speaker interface is something that I have to consider with the design of the speaker, I can't look at this as two discrete problems, but there is only so much you can do not controlling the final placement of the speakers. The tradeoffs and balances are the bane of every speaker designer, starting with a raw magnet and every other material selection that goes into a design. I can appreciate the problems of designing for large scale audio sound systems, I have been there and some day will return when I think I have something unique and productive to contribute.
I appreciate all the time you take to try and answer these rather difficult questions. I am working on a new speaker design for a consumer application and it is not a trivial exercise to do what we know needs to be done when we can't use waveguides due to size limitations. I do have the advantage that I will not have to use a wooden enclosure.
I am molding the enclosure in a high dollar material that has very good acoustical properties. I can shape the enclosure to take advantage of the material, but it is still a design conundrum when you are using two discrete devices, I can move diffraction from one plane into another but can not eliminate them in both the vertical and horizontal planes simultaneously without going with a coaxial design. A coaxial design brings in its own set of compromises that I don't think will outweigh the mechanical limitations of that solution.
The room speaker interface is something that I have to consider with the design of the speaker, I can't look at this as two discrete problems, but there is only so much you can do not controlling the final placement of the speakers. The tradeoffs and balances are the bane of every speaker designer, starting with a raw magnet and every other material selection that goes into a design. I can appreciate the problems of designing for large scale audio sound systems, I have been there and some day will return when I think I have something unique and productive to contribute.
You know, I don't even remember. When you listen to dozens of systems in a few hours it all blurs together. In all honesty, the only ones that I found worthy of even listening to twice were the Linkwitz and the CBT's. A pair of Sony's were OK, but nothing else really got my attention in a good way. Some were so bad that you really have to wonder "what is going on here!" Dave Clark and I walked out of one room shaking our heads and both going "Well those are good examples of what gives horns a bad reputation!"
Earl,
You mean you still don't appreciate the sound of horn honk and the horrid integration of some of these horn systems! It seems so easy to some to design a great waveguide and others just build something that would have been done 50 years ago and think efficiency is the only parameter to worry about.
You mean you still don't appreciate the sound of horn honk and the horrid integration of some of these horn systems! It seems so easy to some to design a great waveguide and others just build something that would have been done 50 years ago and think efficiency is the only parameter to worry about.
HI Tom
Well written, a little long winded, but almost completly in synch with my thoughts as well. Particularly in the single point source idea. My preference would be for a single point from which all sound radiates into a narrow but constant angle, but the ideal is not possible. What then are the best tradeoffs? I think our markets dictate different approaches, but the thing is the an OS waveguide is an idea point source, if done correctly, over the entire bandwidth for which it is functional. The crossover is a problem, which is why I minimize those. Coax with the horn in the middle of the woofer fails the directivity control test because the waveguide is too small. Its all a balance of tradeoffs, but we both have basically the same target. It's too bad that you have never heard my speakers. I am sure you would be impressed.
As to the state of our business, after the AXPONA show yesterday, I have all but given up that audio will ever again be anything more than a very small niche hobby.
A rather academic study that does the problem the hard way. This is a trvial transform problem using the Spherical Hankel Transform as I showed decades ago and in my book. But I guess that they didn't see any of that because none of it is refernecd. (Thats all too typical I am affraid.)
It is a good paper if one needs publications for tenure.
I heard MBL 101. A few years ago, so don't know if it was the MKII version or an earlier one.
There's definetly something wrong with the concept if you want accuracy and a precise image in a small bounded space. And that's very understandable from what we know about acoustics. I'm not arguing about other preferences.
In terms of still hearing the direct signal you're right, but high gain specular energy still greatly has an effect on the sound quality. There's a difference there.
I envy you for having learned from SydAudCon and Don Davis from those days. What I've learned about acoustics mostly came initially out of their teaching, but SydAudCon (from what I hear from older guys) is unfortunately not the same today as it used to be.
Papers like that got Mellow on the title of the latest Beranek "Acoustics .." edition, I assume.
Life isn't fair.
But at least the dipole peak shapes in these studies are closer to reality than what you see at Linkwitz' or Kreskovsky's sites.
Rudolf