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Thread: Building my dream system, need lots of advise!

  1. #31
    Member jmpsmash's Avatar
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    And this is the combined response with the T925A sitting on top of the 2441 body. Looks not bad for a first pass!

    JBL 2397 + Fostex T925A (w/ 2uF series). 24dB HP filter @ 950Hz

    Attachment 85107
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  2. #32
    Senior Member Ian Mackenzie's Avatar
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    On the basis your measurements are correct the issue is both drivers outputs should not be overlapping in the pass band.

    The horn compression driver requires a low pass filter @5000 hertz. A 3rd or 4th order filter to attenuate the horn output above 5000 hertz. The Fostex should have an identical high pass filter @5000 hertz. You are best to do this actively.

    This may require additional active crossovers.

    Alternatively you could try a passive high pass filter on the Fostex at a higher frequency and use the horn drivers natural roll off as the low pass crossover. This will require a simple 3rd order high pass filter such as is commonly used with the Jbl 2405 slot radiator at about 9000 hertz. You may have already tried or considered this so l am suggesting this until you can do a 4 way fully active crossover. Typically this is what JBL does in this scenario with a horn system that requires additional HF extension.

    You need to check the impedance of the Fostex but the parts values would be 1uF, 0.12mH, 1.5uF. I would place an 8 ohm Lpad on the Fostex and then connect the passive filter

  3. #33
    Member jmpsmash's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    On the basis your measurements are correct the issue is both drivers outputs should not be overlapping in the pass band.

    The horn compression driver requires a low pass filter @5000 hertz. A 3rd or 4th order filter to attenuate the horn output above 5000 hertz. The Fostex should have an identical high pass filter @5000 hertz. You are best to do this actively.
    Yes. I was hoping I could avoid having to get another DAC/amp combo to drive the T925A, but from the results of this measurement, I do see that it is unavoidable.

    1. I do see some interference between the two, esp if they are not aligned.
    2. The placement of the T925A aligned with the 2441 is not ideal at all. I would like to put it further front which means adding delay to it via DSP.

  4. #34
    Senior Member Ian Mackenzie's Avatar
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    In the short term you could improvise by moving the Fostex crossover point out to 9000 hertz and use a 3rd order high pass filter like Jbl used for the 2405 slot radiator.

    The horn does not need a low pass filter as it is rolling off above 10000 hertz anyway.

    I would use an Lpad just like in the schematic on the Fostex. This will provide a stable impedance for the passive crossover and allows you to control the level.

    http://www.audioheritage.org/vbullet...5-L-pad-wiring

    This would be JBLs strategy in a situation where the horn system needed additional HF extension.

  5. #35
    Senior Member Ian Mackenzie's Avatar
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    If you want to try this l can post the schematic.

    To attempt a passive crossover at 5000 hertz for both the horn and the Fostex would be quite complicated in this diy situation and would cost you some $$$.

  6. #36
    Member jmpsmash's Avatar
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    just thinking aloud.

    right now my plan is to go with the 2216ND-1, which is supposed to be very usable up to 1250Hz. I am planning to cross it at 1kHz with the 2397.

    I currently have 3 DAC/amps driving the woofers, the 2123H and the 2397/Fostex.

    Now if I can get away without the 2123H by using the 2216ND-1, then I free up one DAC/amp which I can use for the Fostex.

    I read that it is better to cross the 2397 at 5-6kHz, which is my original plan, so I will have to use the DSP crossover anyway.

    So in other words, going with the 2216ND-1 will save me having to pay for DAC/amp which means I save some money doing that. So I should stop delaying and go ahead and order them.

    If that's the final solution, then I might as well save the money and not make any passive crossover. the 2uF I have lying around and it is good for some experiments.

    That' the train of thoughts now at least.

  7. #37
    Senior Member Ian Mackenzie's Avatar
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    If you are going the 2216ND-1 route that all makes sense.

    Btw there is a lot of opinions across all this diy Audio space. One mans paradise is another mans nightmare!!
    I used the 2397 for years with a 2405 passive crossover @8000 hertz and it worked great. But l had to customise the crossover to get a smooth transition.

    You plan to use your existing Dac amp for the Fostex is good. You can try all these options and see what works best for you.

  8. #38
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by jmpsmash View Post
    I read that it is better to cross the 2397 at 5-6kHz, which is my original plan, so I will have to use the DSP crossover anyway.
    You should verify this yourself. I think I’d go the 9KHz route myself.


    Widget

  9. #39
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    FWIW, as I've never built a 4 way, but since you have them, I'd use the 2123 between the woofer and horn and live without the super tweeters until finances allow experimenting with the high frequency. You can get a lot of enjoyment out of the system running up to 10k. If you do cross at 5-6k those drivers will have to mesh perfectly. That's still a pretty critical range.

  10. #40
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    Quote Originally Posted by rusty jefferson View Post
    FWIW, as I've never built a 4 way, but since you have them, I'd use the 2123 between the woofer and horn and live without the super tweeters until finances allow experimenting with the high frequency. You can get a lot of enjoyment out of the system running up to 10k. If you do cross at 5-6k those drivers will have to mesh perfectly. That's still a pretty critical range.
    100% agree with this!

  11. #41
    Member jmpsmash's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    If you are going the 2216ND-1 route that all makes sense.

    Btw there is a lot of opinions across all this diy Audio space. One mans paradise is another mans nightmare!!
    I used the 2397 for years with a 2405 passive crossover @8000 hertz and it worked great. But l had to customise the crossover to get a smooth transition.

    You plan to use your existing Dac amp for the Fostex is good. You can try all these options and see what works best for you.
    Quote Originally Posted by Mr. Widget View Post
    You should verify this yourself. I think I’d go the 9KHz route myself.


    Widget
    Thanks guys. There will be a lot of experimentation for sure and I will post my findings here when I get to that point.

  12. #42
    Member jmpsmash's Avatar
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    Quote Originally Posted by rusty jefferson View Post
    FWIW, as I've never built a 4 way, but since you have them, I'd use the 2123 between the woofer and horn and live without the super tweeters until finances allow experimenting with the high frequency. You can get a lot of enjoyment out of the system running up to 10k. If you do cross at 5-6k those drivers will have to mesh perfectly. That's still a pretty critical range.
    Quote Originally Posted by dkalsi View Post
    100% agree with this!
    I have the 2397/2441 and the Fostex T925A already. Although not integrated well at the moment. Before I got the Fostex, I was listening to the 2397 on it's own. The sound is smooth, detailed, dynamic (esp micro dynamics). I really enjoyed the sound and didn't disappoint after the amount of work to acquire them. They sounded like what I remember them to be from 17 yrs ago.

    They are excellent for vocal but they are missing the top end. At my age I am still able to hear up to 17kHz (thanks to the Fostex to verify that) so for something like a Jazz piece with the high hats and the upper end spectrum in classical pieces (flute, trumpet, oboes, triangles), they are missing something. Also the 2397 don't do placement very well. They don't paint a good image like cones and dome drivers. Adding the Fostex filled in that gap and give the whole presentation a lot more air and imaging.

    I will have to play around and spend extra effort with driver integration.

  13. #43
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by jmpsmash View Post
    Also the 2397 don't do placement very well. They don't paint a good image like cones and dome drivers. Adding the Fostex filled in that gap and give the whole presentation a lot more air and imaging.
    If you can control your first reflections, they can image pretty well. Unfortunately that 120° dispersion pattern is tough to deal with in most rooms.

    I used 2397s and then the Westlake versions many years ago, and I believe I used a 3rd order passive network between the 2441s and the 2405s at around 9-10KHz. The tweeter was offset rearward some distance... unfortunately I don't really remember the details.


    Widget

  14. #44
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    Quote Originally Posted by Mr. Widget View Post
    If you can control your first reflections, they can image pretty well. Unfortunately that 120° dispersion pattern is tough to deal with in most rooms.
    I believe this is a major problem of this horn as just a few people have a controlled listening environment. Due to the size of these horns the speaker-enclosures get very wide and in average sized rooms they will be placed close to the sidewalls. This increases the problem with first-reflections further more...

    I own the 2397 myself and love itīs sound a lot. But I believe in a small listening place a horn with 90° dispersion like the Yuichi A290 could work better...

  15. #45
    Member jmpsmash's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    If you can control your first reflections, they can image pretty well. Unfortunately that 120° dispersion pattern is tough to deal with in most rooms.

    I used 2397s and then the Westlake versions many years ago, and I believe I used a 3rd order passive network between the 2441s and the 2405s at around 9-10KHz. The tweeter was offset rearward some distance... unfortunately I don't really remember the details.


    Widget
    Quote Originally Posted by Dr.db View Post
    I believe this is a major problem of this horn as just a few people have a controlled listening environment. Due to the size of these horns the speaker-enclosures get very wide and in average sized rooms they will be placed close to the sidewalls. This increases the problem with first-reflections further more...

    I own the 2397 myself and love itīs sound a lot. But I believe in a small listening place a horn with 90° dispersion like the Yuichi A290 could work better...
    my room is 20ft wide. right now on the side walls there is a 2x4" diffusion panel on first reflection each side. it was there for my previous pair of regular dome speaker. let me make it 4x4 and see if that makes a difference.

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