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Thread: drawbacks w/ constant directivity horns

  1. #16
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by 4313B View Post
    Does anyone have any money to buy these things from you? Or are you guys getting them second hand?
    I bought one pair factory new as baseline, but all of the others have come from the lowball SoCal vendor of pro drivers with indeterminant provenance....

  2. #17
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by 4313B View Post
    Wow! And you've not suffered a single pinched voice coil? That's amazing. Who is this SoCal vendor? This is where all those 2435's came from too right? What is he charging for these?
    Yes, the same one who provided the flood of 2435HPLs members bought last year. Supposedly "new," but not, apparently.... :dont-know

  3. #18
    Senior Member pos's Avatar
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    Quote Originally Posted by Zilch View Post
    Would you run them on PT-F95HF (the combination I'm mostly building with) and post the curves in an appropriate thread, please, in comparison to 476Be and 435Be?
    I think you already measured them:
    http://audioheritage.org/vbulletin/s...8&postcount=84

    And I posted the comparison here, with the same scale:
    http://audioheritage.org/vbulletin/s...8&postcount=32

  4. #19
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    Quote Originally Posted by pos View Post
    I think you already measured them:
    http://audioheritage.org/vbulletin/s...8&postcount=84

    And I posted the comparison here, with the same scale:
    http://audioheritage.org/vbulletin/s...8&postcount=32
    We've moved substantially further ahead since then, actually:

    http://audioheritage.org/vbulletin/s...970#post204970

  5. #20
    Senior Member pos's Avatar
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    I thought you were looking for raw measurement on the PT-F95HF waveguide?

  6. #21
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by pos View Post
    I thought you were looking for raw measurement on the PT-F95HF waveguide?
    Well, yes, but how well we can get them to play is always a matter of considerable interest, too.

    4313B uses different measurement methodology from what I do, and under better conditions. Whatever he is willing to do will be valuable.

    This is largely uncharted territory, but also a very nice place, in my experience....

  7. #22
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    Quote Originally Posted by 4313B View Post
    Who is this SoCal vendor? This is where all those 2435's came from too right? What is he charging for these?
    I'm sure Zilch is talking about this guy: http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA:IT&ih=024

    I've emailed him before to ask, but he's really dodgy about his sources, though he certainly seems to have them... List his stuff - sometimes he's really got a bunch of decent drivers. Listing his completed items shows what he's been getting, and the deals some people get! I think I've bought some dias. from him before - can't remember...

    John

  8. #23
    Senior Seņor boputnam's Avatar
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    Quote Originally Posted by johnaec View Post
    ...he's really dodgy about his sources, though he certainly seems to have them...
    We'll find him. We're on it...

  9. #24
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    Quote Originally Posted by 4313B View Post
    JBL seems quite interested to discover his source... Evidently he is "just up the street"...
    I'd hate to blow a somewhat hidden but legitimate source - if I remember right, he mentioned he'd built up a bunch of sources, many of which were connections to SoCal sound companies with extra things like those service packs JBL sells for stuff like the Vertecs, where you buy a pack that has a whole bunch of different parts in it, drivers, dias, handles, hardware, etc., (if you dig down in the documentation enough you usually find stuff like that listed where you get a bunch of parts at once), and he was picking up stuff that was mainly left over.

    If he ain't doing anything legally wrong, at least he's been a decent source at times for many... JBL has to be aware of him - he's been around for years.

    John

  10. #25
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    Transcendent?

    Quote Originally Posted by Zilch View Post
    I can only suggest taking the HOM issue up with Geddes himself.

    I run the #3 and #4 drivers on 4313B's above list on 2352s, and find them to be "Transcendent" using either of those.
    Hi,

    Sure these horns sound slick and acute. In spite of being "HOM"-ies as can be. In my understanding there is nothing to argue about with Geddes himself. The HOM-issue should be seen as a somehow missleading speculation - until the claimed effects are made available to common engineering or at least - direct - investigation. Everywhere in HiFi a bunch of wishfull thinking in front of imaginary amazements hinders clear sight, people are to much used to it.

    If I liked to stick with JBL, I take the el cheapos. The off axis performance seems to be great. No HOM but plain spherical radiation. There's an issue with loading though. The raise of THD that You measured with lower frequencies is a remarkable finding. I didn't see such with other smaller horns - e/g RCF H100 and appropiate drivers. My medium format horns - EVs and JBLs - did the other way round: high THD at high frequency and lowering THD way down to some distinct lower cut/off. Below the latter a sudden rise of THD with queasy noises.

    I understand that the vintage CD approach has to be taken as it is. I was curious on what people - if any - do with the leakage of lower hights off axis. It seems that the alternative is to accept or split up with it.

    Thanks a lot

  11. #26
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    I wouldn't consider my distortion measurement definitive of anything. You can see me asking how to do it there.

    Geddes's analysis of his measurements of the cheapo JBL waveguide is at variance with my own, of course. I tried to elicit some discussion of the results on that forum without success. It seemed as though most everyone was more interested in using the thread as a platform to forward their own off-topic agendas.

    Nobody ever seems to get down to the head-to-head competition data comparing the EQ'd waveguides' performances. At worst, I don't see how anyone can conclude that the JBL "horn" did anything less than remarkably well....

  12. #27
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    Quote Originally Posted by Zilch View Post
    I wouldn't consider my distortion measurement definitive ... head-to-head competition ...
    Zilch,

    It ain't easy to purchase JBL parts at reasonable prices in Germany. I'm near to ask Guido for some el cheapos. As soon as I get a pair I'll offend You with my own measurements ('hope You get the irony).

    btw: http://www.fesb.hr/~mateljan/arta/

    Measure distorsions via a method found by Mr. Farina, that is deconvolution of a log swept sine, transforms the HD components in time domain to seperate impulse responses, in the end gives HD f.response. You should give it a try. Acurate HD2 and HD3 within seconds for the whole spectrum.

    Jurgen

  13. #28
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    Mini,

    You raise an interesting point about distortion and low end directivity.

    Most of the el cheapo CR horns of the PT type were made for integration into some of JBLs SR systems where they were crossed over at 2K hertz and above from a matching PT midrange wave-guide. ie they are not intended for 800 hertz crossover. The increase in distortion is the result of the driver dias being unloaded and increase in excursion.

    As far as domestic home audio goes according to Geddes, there is little point in controlled directivity with horn loading below 1000 hertz for home use but he does recommend matching the dispersion of the woofer and the horn at the crossover point. Typically this is 1000-1200 hertz for a 15 inch woofer. To properly load the driver this requires a large wave-guide of 15 inches or more.

    This is based Geddes overall approach to understanding small room acoustics in relation to what is important to the human ear as a result of his scientific study. (less than 25 sq metres)

    The problem is people shy off from large horns and wave-guides and try to use smaller devices and they wonder why the $299 Ipod dock sounds better than the diy speaker.

    My recommendation is leave it to the experienced loudspeaker engineer and build a proven diy system than base your project on a lot of ad hoc data posted on numerous forums.

    Geddes paper on his Suma system is quite a valuable read if an understanding of what a loudspeaker does in a room is desired. To appreciate what Geddes is saying you need to read the paper several times because the complexity and the number of dimensions to the discussion.

    Geddes also markets a wave-guide to his design.

    Many of todays domestic loudspeakers are designed for not what looks good on paper on and off axis but how they perform in a domestic home listening room in so far as the response and dispersion in the reverberant field is concerned. Some of the more recent JBL Consumer 2 way systems are designed along these lines as opposed to the older 43XX blue baffle series (JBL Japan range)

    CD or no CD ie a direct radiator it really comes down to specifics and your particular needs..assuming you understand what they are.. But people still like to make a labour of love out of doodling with all sorts of drivers and horns like they were coming of a conveyor belt.

    If your are interested Acoustic Elegance are working on a large wave -guide for the Diy market to mate with their 15 inch drivers. I have no affiliation but their products appear to be very well made and are value for money for the diy market

  14. #29
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    Geddes teaches that horn loading is a concept derivative of old-school horn theory which does not apply to waveguides.

    He also teaches that distortion as we know and measure it is irrelevant to sound quality.

    JBL uses some mighty small horns in its current TOTL monitors, down to 1 kHz:

    http://manuals.harman.com/JBL/HOM/Te.../4348%20ts.pdf

    They ALSO use some rather larger ones at 750 Hz:

    http://manuals.harman.com/JBL/HOM/Te.../4338%20ts.pdf

    Go figure....

  15. #30
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    I said earlier it comes down to specfic of the design.

    JBL know what they are doing

    Specifically the PT devices you have been rooting around with in retard mode are not but you keep trying to make it work.

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