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Thread: Group Delayed Speakers, anyone?

  1. #16
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Zilch
    It also matched the profile of the new Bob's Big Boy counter that had just opened down the street, where everybody had lunch.
    I thought that was a closely guarded JBL secret.

    I think, " Because it looked cool, most likely." gets the nod.

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  2. #17
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    Quote Originally Posted by boputnam
    Dammit, Giskard!!
    Do it now! - your Gov's inflection.

  3. #18
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Giskard
    Do it now! - your Gov's inflection.
    I guess I don't spend much time thinking about the Governator. It took me until now to figure that one out.

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  4. #19
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    "But this enginneer's main income is from designing analyzers for coffee roasting(among others), that he said all roasters use. I also tried his coffee(mohca expresso), every bit as good as his speakers."

    Well most Hi Fi inventors have some sort of pre market entry occupation like Duntech and lesser knowns like Metaxas who are shall we say known cons who lure wealthy people into parting with lots of money for an illusion they lust after.

    On reading early literature by Duntech, he refers to things other than physical time domain for imaging and stage depth. Moreover impulse response step function was the main feature of his designs, all 6th order minimal phase crossovers. The drivers were almost exclusively Dynaudio or Scanspeak, noted for transient attack and the alignment of the coincident sources combined to offer true 3D imaging. The thing was his speakers came with full test reports backing up his claims, no snake oil, audio mythology required here. And yes I have owned a set of Dutechs which I reluctantly sold when one time when I relocated.

    Review on the Sovereign in Electronics Australia - January 93

    "What most audiophiles regard as the best loudspeaker system in the world; the almost legendary Duntech Sovereign.

    "I have not heard any loudspeaker system which could out-perform the Sovereigns in terms of spatial localisation..this is as close as you will get to a live recording at home.

    "Without hearing them, you will never appreciate just how outstanding these speakers are...sounds that are about as true-to-life as you could hope or want to achieve in a residential situation."

    Harry Pearson reviews the Sovereign in The Absolute Sound - September/October 1991

    "What it does have, aside from an unusually life-like ability to deploy an orchestra across the expanse of your living room, is the most uncanny ability to suggest...the sound of real bass instruments playing individually or en masse and doing so with the kind of authority you will find chilling..."

  5. #20
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    This may seem like information overload but I found the answers to specific questions most interesting:

    Q4.1 A lot of hype is used to describe loudspeakers and I do not understand any of it. Is any of this stuff useful or is it all advertising techno-babble?

    Answer: To a loudspeaker designer who lives and breathes loudspeakers the terms phase, amplitude, nyquist plot, and waterfall are as familiar as sky, tree and car to a normal person. So lets back up and take a fresh look at loudspeaker measurement. In my answer to this question I have restricted myself to the on-axis response, that is, what does the loudspeaker sound like when it is pointing at you.

    In the early days of hi-fi, when two loudspeakers which "measured the same" sounded entirely different, the popular notion (even amongst early designers) was that loudspeaker measurements were completely meaningless. What they were measuring was the first and most simple characteristic of how loud it plays, which we call "amplitude". The amplitude is how loud the speaker is at different points on the musical scale. If a pianist plays every note at the same volume, then they should also sound the same volume through a loudspeaker. But that is only the first paragraph of a long story.

    It was not until the late Richard Heyser wrote penetrating and lucid AES papers about the time behavior of loudspeakers, that it was even possible; in principle; to measure loudspeakers meaningfully. His great breakthroughs related to the effects of phase upon the sound of a loudspeaker. Basically his insight (in this specific area) was that the apparent position of a loudspeaker had something to do with its phase.

    *footnote: Phase is the measure of whether one thing is in step with another. To illustrate this, imagine that the Salvation Army band is marching by in a parade. If you look at their feet, you will notice that the right foot of every man moves forward at the same instant. The feet in this band are in phase with each other. Contrast this with a crowd on a city street; there is no relationship between the feet - they are completely out of phase.

    If the phase and the magnitude of a loudspeaker were not locked together in an intricate dance called "minimum phase", then the speaker would appear to be at several places in the room at once, stretched out in a line from the listener, through the speaker, and out to infinity. In order to prove this hypothesis, he designed equipment which could measure phase. The problem was, that measuring phase this way was about as easy as balancing three eggs one on top of each other. Partly to solve this problem, he devised "time delay spectrometry". I won't go into TDS here, but suffice it to say that this was a revolution in loudspeaker measurement. With TDS you could also see the time response of the speaker.

    This brings us to the next important loudspeaker measurement which is called the Waterfall plot (or Cumulative Spectral Decay to scientists and engineers). This plot displays how loud the speaker is at all frequencies (called the Magnitude response by the same people) at each instant in time. These plots are shown one after each other, like cards in a deck. The effect is like looking at a cliff face. The steeper the cliff the better.

    As time passed, the Maximum Length Sequence system was perfected and offered by DRA Labs in their MLSSA package. This allowed engineers to process their measurements in all sorts of interesting ways. One plot, which shows a huge amount in once glance, is the Nyquist plot. In this plot, the loudness and the phase are displayed like the hands on a clock. The longer the hand, the louder the speaker and the hour the hand is pointing to is the phase. In this system, 3 o'clock is zero degrees, 12 o'clock is 90 degrees, and so forth. As the frequency rises the hand traces out a line on the clock face and this is the plot you get. A ideal loudspeaker would show a straight line going from the centre out to some distance and then squiggling around in a tight little bunch for all frequencies (So far as we know the only conventional loudspeaker which does this is the Duntech Prince).

    So in summary if the manufacturers had the nerve all they would need to show you is the waterfall plotm and the Nyquist plot and you could tell virtually everything you need to know about on axis response.


    <TABLE cellSpacing=0 cellPadding=0 width=500 border=0><TBODY><TR><TD>Q3.1 What makes a good loudspeaker?

    Answer: A good loudspeaker creates the illusion of being at a musical performance and lets you hear the emotional message that the performer has woven into the music.

    At first this might seem to be the wrong answer, particularly if you are of a technical bent. Some designers might say, "The magnitude and phase should be so and so." or "The cumulative spectral decay must exhibit x dB of clean decay in the first y milliseconds". For Duntech, there are a myriad of measurements and assessments which must be performed before the loudspeaker is approved for shipping. Above and beyond all the measurements, the final decision on each pair of speakers is always made after intense listening sessions.

    Q3.2 Can you tell anything by looking at a speaker?

    You can actually tell a lot just by looking at the speaker. If certain features are not attended to you will not get very close to the sound you are looking for. When you look at the speaker, does it use more than one driver of each type? Two drivers sharing the load will not go into overload as easily as one and will be more dynamic and more natural sounding than one.

    Does the speaker have time collimation of the drivers? If the drivers are not arranged so that all sounds arrive at the listener at the same time, then the music will be scrambled. The reason why most speakers have flat front baffles is because it is cheaper to build them that way, not because it sounds better.

    Does the cabinet use diffraction control? The best way to control diffraction is to use felt. The felt must be cut into all sorts of shapes to work best where they are placed. The second best way is to use a curved or sculpted baffle. We have built speakers with curved enclosures (spherical even!) and the listening tests confirm what the measurements say: felt is the only way to go.

    Q3.3 My friend says that the "rap test" is a sure fire way to pick a good speaker, what do you think?

    If you rap on the side of a speaker with your knuckle and it produces no sound or a dull tuneless thud then it is adequately braced. If the speaker sounds like a tympani then it will colour the sound. There is more to this than meets the ear though. Some manufacturers have gone to huge lengths to control cabinet resonance and then ignored the matters of diffraction, crossover design and driver selection. It is as if someone has built a house with a safe door from a bank for the front door, and put a flimsy screen door with the hinges hanging off on the back door.

    Q3.4 What is pulse coherence?

    Answer: Pulse coherence is the name we give to the package of properties which makes a Duntech loudspeaker what it is from a measurement standpoint. A pulse coherent loudspeaker produces a sound which is "in step with itself" and is not muddied by diffraction from the cabinet. Technically, the sound is in step with itself when the summed response of all drivers working together preserves the original electrical waveform which was fed into the speaker. If you were to look at the input voltage waveform on an oscilloscope and then the measured sound using a microphone placed at 3.5 metres you would see exactly the same shape. Amazingly, very few loudspeakers actually do this. Pulse coherence is part of the Duntech design philosophy.

    John, I trust your still with us, Hopefully this will help purify what you think you know rather than rely too much forum chat waffle from those all over or parts unknown.



    </TD></TR></TBODY></TABLE>

  6. #21
    Webmaster Don McRitchie's Avatar
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    The "Dun" in Duntech stands for John Dunlavy, the company's founder. In the early 90's, John sold Duntech and moved back to the States to found DAL (Dunlavy Audio Labs). DAL was very highly regarded, but became a victim of the Asian financial crisis that saw their major market disappear. They closed their doors in 2002. Duntech continues on and the philosophy espoused in the above posts comes directly from John Dunlavy.

    In 1998, I had the privilege of meeting John and spending around 5 hours with him at his plant in Colorado Springs. I listened extensively to their systems, including their equivalent to the Duntech Sovereign. To this day, I would say these systems were the most accurate, holographic speakers I have ever heard. They made me a believer in phase and time alignment. However, like all speakers, they are not perfect. Achieving time and phase alignment dictates that cross-overs must be 1st order with 6db slopes. This means that the drivers have to cover a very wide frequency band and this limits their power handling. The drivers themselves lack the power compression defeating technologies that are the hallmark of JBL so that they are not linear with power.

    Nonetheless, my dream would be to own both a TOTL Dunlavy and a TOTL JBL (like Project May ). Each excels in their own domains.

    BTW, a very good combination of these approaches is the 250Ti. This is one of the few JBL's that is both phase and time aligned.
    <SUP></SUP>
    Regards

    Don McRitchie

  7. #22
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    Thanks Don,

    I just called the web page contact Ph in Aust and was advised the company that was in Aust has been acquired by Orpheus Loudspeakers.

    There is a limited part of the original Classic range being made at the moment and there will be a new range released later in 2005.

    http://www.duntech.com.au/images/all.html

    <TABLE id=table6 cellSpacing=0 cellPadding=8 width=560 border=0><TBODY><TR><TD class=heading vAlign=top align=left width=560>Company Profile<!-- end include --></TD></TR><TR><TD vAlign=top align=left width=560><!-- start include -->Orpheus has been in the business of designing and manufacturing high fidelity audio speakers for 20 years. The company has a solid base in Australia with two separate facilities in Sydney; one for design and testing, the other for warehousing and distribution.

    The company’s commitment to excellence along with its years of experience in designing high quality and high performance audio equipment has led to the growth of a substantial following in Australia. This is true for the consumer range as well as for the company’s commercial studio and reference equipment. Orpheus Audio professional users in Australia include ABC Radio and TV, Studio 301 (formerly EMI Studios, Sydney), Channel 10 and Channel 7 TV Studios. Orpheus also sells through a very select dealer network in Australia comprising 20 of the best hi-fi stores in the country.

    In 2004, Orpheus Audio acquired Duntech Audio Australia Pty Ltd – a very highly respected name in the audio industry worldwide. Duntech loudspeakers have been acclaimed by many highly respected and widely read international audiophile magazines, including Audio, Australian Hi-Fi, Digital Audio, Gramophone, HI-FI Choice and Stereophile.

    Orpheus Audio – now bolstered by its Duntech resources and expertise - has an ongoing research and development program to refine and improve its technologies and performance across its entire range of products.

    </TD></TR></TBODY></TABLE>

    <DT>DUNTECH AUDIO </DT>
    <DT>12A Lime Kiln Road, Lugarno. N.S.W. 2210 </DT>
    <DT>Telephone: 61 2 9584-0743
    Fax: 61 2 9584-1708 </DT>

  8. #23
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    Here is a link to other Aust speaker manuacturers, notable are Krix Loudspeakers, Whatmough Monitors, Legend Acoustics, VAF Reseach and Whise Precision Audiohttp://home.vicnet.net.au/~macinc/

  9. #24
    hector.murray
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    News?

    Any News from "Mr Grounds" or has MJC gone silent?

  10. #25
    Administrator Robh3606's Avatar
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    Hey Ian


    Thanks for the link! There is some real nice stuff on the site.

    Rob

  11. #26
    Administrator Robh3606's Avatar
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    Hello Don

    Have you ever read the Stereophille review on the L250's?? I would love to scan and post it to get owner reactions. Let's just say it has a few twists and is not that favorable.

    Rob

  12. #27
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    I did a review of Stereophile once.
    I found the pages to be too rough to wipe with - which means it has virtually no redeeming value whatsoever.

  13. #28
    hector.murray
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    ROFLMFAO

  14. #29
    MJC
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    Quote Originally Posted by hector.murray
    Any News from "Mr Grounds" or has MJC gone silent?
    I haven't been on this site since I started this thread. And have been too busy to get back to Carl Staub, the engineer of the speakers I was referring to.

    whej4312 quote
    In your L-212's case, driver placement on the baffle plane is a big problem. The baffle is much to wide to make the L-212's behave like a point source. Damping the face acoustically helps a ton.

    If you paid attention to my Avatar you would see that my main pair of L212s are mirror imaged, and DO act as a point source. They image better than most speakers I've heard of late. They DO give me a better soundstage than my original L212s. I do have another pair of L212s that are treated with foam stuck to the inside of the grille that I bought on Labor Day weekend. But right now they are used as back channel speakers. Maybe this weekend I'll put them side by side my mirror imaged to do a comparision.

    Being I haven't heard my L212s side by side with Carl's speakers I can't really tell how much better the soundstage is, if at all, other than his soundstage seemed to be much deeper.

  15. #30
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    Quote Originally Posted by MJC
    If you paid attention to my Avatar you would see that my main pair of L212s are mirror imaged
    Your avatar does look pretty neat MJC. It appears you did a great job reworking your L212's.

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