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Thread: Horn/Waveguide Questions

  1. #31
    Senior Member ivica's Avatar
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    Quote Originally Posted by sebackman View Post
    Hi Rob,

    The newer VTX WG has a better high end and better horn load in the low segment. I think I have posted a comp earlier. -Will see if I can find the comp file.

    Can it be fixed with DSP? Absolutely, but given a choise with no price difference why would you not get the better start?

    kind regards
    //Rob2
    Hi

    Talking about STX 825
    https://jblpro.com/zh/products/stx825
    https://reconingspeakers.com/product...006815-stx825/


    Regards
    Ivica

  2. #32
    Member sebackman's Avatar
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    Hi everyone,

    Yes Ivica, they look the same but they are not. I have really sold all my vintage and other "high end" horn/waveguides and only use these or the M2 (and soon the 4367). If you can handle that they are ugly, cheap, plastic (not nice wood or cast metal) and with limited "show-off factor", they really out perform most alternatives on the market for a song. Slab some vibration damper material (rubber or similar) on the outside of the plastic plastic and make a sturdy driver support in the cabinet and you are good to go. At least with 2450SL, 2451SL and 2452SL. 2453 will need a spacer and the goes for 243X. Same problem on the M2, a nasty resonance in the throat at 10k.

    Older PT's are also good, no doubt. With some additional EQ and measuring I guess you can potentially get to the same point. These are just a newer version.

    If you do go the 4" SL route, which I strongly suggest, get new diaphragms as older may be out of spec dependent on prior use.

    I also suggest to open the back cover on drivers prior to purchasing to check for corrosion in the drivers. If the have been in PA operations they may have been in stage monitors that from time to time get water in the horn entrance or may have been subjected to condensation at outdoors events. If the driver is rusty under the rear cover (you normally do not need to remove the diaphragm to see it) I would stay away as my experience show that it is very difficult to get them to perform. If the pole piece is corroded that often means that there may be corrosion in the phasing plug and that cannot be cleaned without dismantling the entire driver. A hve bought many "bargain" drivers that turned out to be beyond HiFi use. PA probably fine but not for critical listening.

    Another topic I have not seen mentioned here at LHF is Neodym magnet rot. The older JBL drivers used Neodym magnet material that also tend to corrode/rot in certain environments. This materializes as small magnetic fragments in the coil gap and regardless how many times you clean they keep coming back. This means that the magnet is beyond salvage. I have had this on a few 2450SL/2451 drivers that had to be canned. I have also had it on a few older Neodym woofers like the 1400PRO (currently 3 dead basked in the shop). JBL knows of the problem and has also replaced a bunch back when.

    My 25 cents

    //Rob
    The solution to the problem changes the problem.
    -And always remember that all of your equipment was made by the lowest bidder

  3. #33
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    Well this is interesting. I've got a fair number of Neo drivers in various JBL boxes some coming up on twenty years old. Can you point me at any documentation on the Neo 'rot' issue?

    Quote Originally Posted by sebackman View Post
    Hi everyone,

    ...
    Another topic I have not seen mentioned here at LHF is Neodym magnet rot. The older JBL drivers used Neodym magnet material that also tend to corrode/rot in certain environments. This materializes as small magnetic fragments in the coil gap and regardless how many times you clean they keep coming back. This means that the magnet is beyond salvage. I have had this on a few 2450SL/2451 drivers that had to be canned. I have also had it on a few older Neodym woofers like the 1400PRO (currently 3 dead basked in the shop). JBL knows of the problem and has also replaced a bunch back when.

    My 25 cents

    //Rob

  4. #34
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    I've got a set of 2430h drivers that have the magnet rot thing. I cleaned the gap as best I could and they now work. They don't perform that well to my ears. I think the rot continues and I would have to continually clean them as they degrade further over time. So they are sitting on a shelf here. The diaphragms look OK but the drivers do not. I don't have any test equipment.

  5. #35
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    Quote Originally Posted by sebackman View Post
    Hi everyone,

    Yes Ivica, they look the same but they are not. I have really sold all my vintage and other "high end" horn/waveguides and only use these or the M2 (and soon the 4367). If you can handle that they are ugly, cheap, plastic (not nice wood or cast metal) and with limited "show-off factor", they really out perform most alternatives on the market for a song. Slab some vibration damper material (rubber or similar) on the outside of the plastic plastic and make a sturdy driver support in the cabinet and you are good to go. At least with 2450SL, 2451SL and 2452SL. 2453 will need a spacer and the goes for 243X. Same problem on the M2, a nasty resonance in the throat at 10k.

    Older PT's are also good, no doubt. With some additional EQ and measuring I guess you can potentially get to the same point. These are just a newer version.

    If you do go the 4" SL route, which I strongly suggest, get new diaphragms as older may be out of spec dependent on prior use.

    I also suggest to open the back cover on drivers prior to purchasing to check for corrosion in the drivers. If the have been in PA operations they may have been in stage monitors that from time to time get water in the horn entrance or may have been subjected to condensation at outdoors events. If the driver is rusty under the rear cover (you normally do not need to remove the diaphragm to see it) I would stay away as my experience show that it is very difficult to get them to perform. If the pole piece is corroded that often means that there may be corrosion in the phasing plug and that cannot be cleaned without dismantling the entire driver. A hve bought many "bargain" drivers that turned out to be beyond HiFi use. PA probably fine but not for critical listening.

    Another topic I have not seen mentioned here at LHF is Neodym magnet rot. The older JBL drivers used Neodym magnet material that also tend to corrode/rot in certain environments. This materializes as small magnetic fragments in the coil gap and regardless how many times you clean they keep coming back. This means that the magnet is beyond salvage. I have had this on a few 2450SL/2451 drivers that had to be canned. I have also had it on a few older Neodym woofers like the 1400PRO (currently 3 dead basked in the shop). JBL knows of the problem and has also replaced a bunch back when.

    My 25 cents

    //Rob
    Hi Rob,

    can you please share the p/n's for this new generation of PT waveguides, and where to get them?
    Looking at the link Ivica posted, this is an older version of the VTX F12 waveguide?
    I was about to purchase this and the PTH-1010HF-1 from the Speaker Exchange

  6. #36
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    Hello All,Lately I have been trying to settle on a CD / waveguide combination. I seem to like the JBL D2 2430H CD and the current version of the rectangular PT95 90 X 50 degrees. The thinking is that there is less reflection off the walls and especially less off the floor and ceiling.See the attached on axis FR plots and distortion plots attached below.Thanks DT

  7. #37
    Senior Member 1audiohack's Avatar
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    Hello DT.

    Is that wave guide PN5006815?

    There is an issue with attachments that can be worked around in settings.

    I havenít tried yet so I will see if I can send this to you so we can see what you have attempted to attach.

    https://www.audioheritage.org/vbulle...1&d=1669352772

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  8. #38
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    Quote Originally Posted by DualTriode View Post
    Hello All,Lately I have been trying to settle on a CD / waveguide combination. I seem to like the JBL D2 2430H CD and the current version of the rectangular PT95 90 X 50 degrees. The thinking is that there is less reflection off the walls and especially less off the floor and ceiling.See the attached on axis FR plots and distortion plots attached below.Thanks DT

    https://www.diyaudio.com/community/t...382609/page-26

    So are you saying your guessing these ceiling reflections or you can measure it?

    If you are using REW you can factually determine the 1st reflection points in any room with appropriate measurements. REW can also accurately model your room reflection points and room modes.

    Another way is to measure the vertical polar pattern and then work out where the 1st reflection point actually is off the ceiling.

    Hint. This is why 90 x 40 radial horns have found favour in certain situations.

    Depending on the degree of controlled directivity in the 90 x 50 wave guide and your listening distance of those 1st reflections given your ceiling height will be a problem or not with the direct sound from the on axis.

    For example if your listening distant is 2 metres and the ceiling is 2 metres above your ears the reflected path length will be more than 4 metres.

    Edit my post got chopped

    What l was going to suggest is to try the psycho acoustic smoothing function is the REW measurements. That filter provides a good indicator of what really matters. In other words aspects of your measurements require attention.

    In a domestic situation most if not all people put up with 1st reflections because they donít have a choice without installing acoustic panels. Itís a first world problem.

    By selecting a particular listening position you maybe able to reduce the impact of ceiling 1st reflections. Typically this means listening closer to the loudspeaker than you might otherwise do without making some informed decisions.

    Good luck

    Ian

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