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Thread: New Mid horn experiment

  1. #1
    Senior Member eso's Avatar
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    New Mid horn experiment

    It's been while since I've posted any content here. Let's see if any server maintenance has made things any easier...

    In another thread I posted about saving drivers from a really old pair of Monitors that had been abandoned: 4X Gauss 4385A 15" and a pair of TAD TD4001. My original thought was to recreate something like a Westlake large format 2 or 3 way design using the Gauss & TAD drivers. Then I stumbled onto a batch of TAD TW-1601a 15s and started thinking more along the lines of Exclusive 2401/TAD TSM-1 2-way systems. It's a pretty straight forward large 2-way and having built Yuichi A290 radial horns in the past nothing in the build is beyond our doing.

    But being me I can't keep it that simple. For HiFi use I'm not a fan of mid horns with vanes for dispersion enhancement. The TAD TH-4003 horns are supposed to have improved dispersion without vanes. While there are pictures of them, there's remarkably little technical info or drawings available on them. And that horn is made for the smaller throat 40mm of the TD-4003.

    Studying what info is available I designed an APAXIAL (Asymmetrical Pattern, AXIs And Level) radial horn based on the TH-4003 but for the larger 50mm throat of the TD-4001. I am guilty of hubris. Initial tests look pretty good. The traces attached here are raw with no smoothing. Tests are crude as I am in a civilian air traffic pattern and it's noisy here.

    Based on this I now need to try to design the AFAST (Acoustical Filter Assisted System Tuning) which is really a Helmholtz resonator in the upper horn surface. While working out the general idea for this project I happened to meet a former TAD R&D engineer who is digging up some of the tech data on the TH-4003 for me...

    But overall, the initial results look promising.

    eso
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    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

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    @Eso.... chapeau bas .... (for your skills) ...Karel

  3. #3
    Administrator Mr. Widget's Avatar
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    Yes, nicely done!

    For your 2" version, did you scale up the entire horn, or did you focus on the throat area? I noticed you made your throat adapter out of a block of wood where you must be transitioning from the round exit of the TD-4001 to the square opening of the horn. The TH-4003 adapter plate and how it fits to the TH-4003 always surprised me. The adapter transitions from a 1.5" circle to a 1 9/16" square and makes the transition in a distance of 1 5/16" however the opening of the wooden portion of the horn is a little over 1 5/8" inches so it there is a weird step. I would expect this discontinuity to cause issues, but on the TD-4003/TH-4003 measurements the result is stunningly linear. The image below is of one of my resin castings from the TH-4003 adapter plate.

    Since you are using the TD-4001 driver, not only do you have a driver with a larger exit you also the traditional longer internal throat from the original Western Electric design. I imagine this will react to the transition differently as well.

    Do you have any technical information on the AFAST concept? I was unable to figure out what the purpose for it was and all I found on the topic was flowery audiophile prose. When I cloned the TH-4003, I initially included the AFAST port. I had an original TAD manufactured TH-4003 and I carefully measured the port and duplicated it and the foam plug within the port. From my measurements it lowered the FR a bit in the region around 2KHz. As it turned out since I used a much denser material than the maple ply that TAD used my horn had a flatter frequency curve without the port so I omitted it.


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  4. #4
    Senior Member 1audiohack's Avatar
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    Hello ESO;

    Those look great and the measurements are encouraging as well.

    I am also interested in how you made the bent sides.

    Thank you for sharing and please continue with us here.

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

  5. #5
    Senior Member eso's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    Yes, nicely done!

    For your 2" version, did you scale up the entire horn, or did you focus on the throat area?...

    Since you are using the TD-4001 driver, not only do you have a driver with a larger exit you also the traditional longer internal throat from the original Western Electric design. I imagine this will react to the transition differently as well.

    Do you have any technical information on the AFAST concept?...


    Widget
    I didn't scale up a 4003. I did try to use the asymmetric form of the TH-4003 in this horn. It is a 290Hz exponential flare with a .7 hyperbolic influence. I choose 290Hz because the best old Yuichi radial is the 290Hz hyperbolic and it works exceptionally well with a TD-4001. The Yuichi is also quite similar to a TH-4001.

    Once I had run the calculations for the expansion I began a process of drawing a plan view with an 80˚ horizontal spread that transitioned smoothly from the 10˚ conic flare on the driver and the 49.2mm throat. The bottom piece of the horn is mostly a 15˚ radial wave guide. All of the nuance of the exponential expansion happens in the top piece. Another feature of the TH-4003 is that the vertical section narrows initially; this is like a polite version of the old bi-radial designs that established their pattern in one plane and then the other. That narrowing really helps improve the off axis pattern without adding vanes to the horn like the Yuichi of TH-4001. So I'd draw a plan view, calculate the radial segment lengths and then use those to determine section heights and then use those heights to draw a section.

    It took a few tries adjusting throat radii (which also altered where the straight 80˚ section started) and redrawing the sections before I got to something that looked right enough to me. It's really just an intuitive kludge.

    And the mounting plate is 1 3/4" thick with a correct 49.2mm throat for a near exact match with the driver. The horn is calculated from that driver throat flare and area, so the mounting plate is also the throat of the horn and a lot of effort went into making the flare in that area correct with the smoothest transitions possible. From the looks of the initial tests I think I may have gotten pretty lucky on my guesswork.

    I've met a person who worked for TAD and on developing the TH-4003 and the full monitor using that driver and horn. He's trying to recover some of the files on that from an old google drive account. But the AFAST in the horn is really just a tuned Helmholtz resonator. The question the remains is what anomaly is that resonator working on.

    Also, I'm told in the monitor enclosure they added AFAST Helmholtz resonators tuned to the frequency of a standing wave in the ports. I'm told those had major positive results. I'm hoping to get a copy of some of the notes on these.

    eso
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  6. #6
    Senior Member eso's Avatar
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    Quote Originally Posted by 1audiohack View Post
    Hello ESO;

    Those look great and the measurements are encouraging as well.

    I am also interested in how you made the bent sides.

    Thank you for sharing and please continue with is here.

    Barry.
    Barry,
    For this prototype the sides are laminated from 5 pieces of 3mm Baltic birch ply using a form and my vacuum press. Once set, the resulting pieces are dense and rigid.

    eso
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    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

  7. #7
    Administrator Mr. Widget's Avatar
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    Very interesting info on the horn design and shape… makes sense on the AFAST and aligns with what I found. Thanks for the detailed explanation of your design and fabrication processes.

    I have also used a vacuum bag to form curved shapes. Never used veneers as thick as 3mm. Did you get some spring back? I would have expected some.

    Very nice results.


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  8. #8
    Senior Member eso's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    I have also used a vacuum bag to form curved shapes. Never used veneers as thick as 3mm. Did you get some spring back?...
    Very nice results.


    Widget
    Not 3mm veneers, but 3mm Baltic Birch ply, so each of my layers were already 3 layers. These are all run with the face layers' grain running with the bend. When I do larger radii I rotate each layer 90˚ so I get a consistent edge, but the throat radius is a bit tight for that.

    There was minimal spring back and I did account for a bit in the form.

    I'm working towards building a pair of not-quite-clones of Exclusive 2401/TAD TSM-1 monitors. If I proceed with this horn design the horn sides will be laminated and veneered extending all the way out to the cabinet edges with the top and bottom pieces remaining the natural plywood exposed edges. For that design the side pieces will need to be 1" thick +, and I might use 1/8" bending poplar which would have pretty much no spring back in a glue up like that. The plan is for teak veneers with an oiled finish with the horn flares shellacked and very fine sanded for a satin finish.

    That's kind of a nod the the JBL Everest design

    eso
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    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

  9. #9
    Senior Member 1audiohack's Avatar
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    Hello eso;

    That rendering gets my attention. I have a fondness for for the bass presentation of double wide 15” woofers. I think I have everything JBL ever built with that configuration.

    I have only used my vacuum press on flat work. It’s time to get more creative here.

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

  10. #10
    Senior Member DerekTheGreat's Avatar
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    Lots of cool stuff here, love the renderings and seeing stuff made from wood like that. You have some skills!

    Quote Originally Posted by 1audiohack View Post
    Hello eso;

    That rendering gets my attention. I have a fondness for for the bass presentation of double wide 15” woofers. I think I have everything JBL ever built with that configuration...

    Barry.
    Hey Barry!

    If you ever decide to sell those 4435's, remember me! Or you could will them to me.. Not that I've heard a set, but they look great and I'm intrigued about this dual 15" bass presentation. Not sure the 15"+15" coax in my 813C's count as I'm not using them much below 90hz, but they certainly provide a nice midbass thwack, something I've never experienced in another speaker and something I don't think I could live without now.

  11. #11
    Senior Member eso's Avatar
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    Quote Originally Posted by DerekTheGreat View Post
    Not sure the 15"+15" coax in my 813C's count as I'm not using them much below 90hz, but they certainly provide a nice midbass thwack, something I've never experienced in another speaker and something I don't think I could live without now.
    The first time I fired up the first pair of 813Bs that I built I loved what they did for rock drums. I've never been a big Led Zeppelin fan, but those speakers made me want to crank John Bonham.

    And I'd guess the 815 would be even more so.
    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

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    Senior Member DerekTheGreat's Avatar
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    Quote Originally Posted by eso View Post
    The first time I fired up the first pair of 813Bs that I built I loved what they did for rock drums. I've never been a big Led Zeppelin fan, but those speakers made me want to crank John Bonham.

    And I'd guess the 815 would be even more so.
    I absolutely love what my 813C's do for drums!! So much so that I think I've become a percussion freak, even the high-hat (cymbal? I don't even know what it's called...) sounds phenomenal on these, so life-like. To think I thought it couldn't get any better than my XPL200's, now I just see those as a consumer speaker. I love Zeppelin, but didn't even think to try them out, guess I figured their material wouldn't be mastered all that well. I was very disappointed with the Stones, so flat and boring or irritating on the ears for the most part. Which tracks do you recommend from Zeppelin? Think of rockin' In My Time of Dying, Bonham beats the crap out of his kit in that one...

    Definitely intrigued as to how a set of 815's would sound, B or C variant.

  13. #13
    Senior Member eso's Avatar
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    Quote Originally Posted by DerekTheGreat View Post
    Which tracks do you recommend from Zeppelin? Think of rockin' In My Time of Dying, Bonham beats the crap out of his kit in that one...

    Definitely intrigued as to how a set of 815's would sound, B or C variant.
    Physical Graffiti is one of their better mixed records. Start out with Custard Pie...
    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

  14. #14
    Senior Member DerekTheGreat's Avatar
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    Quote Originally Posted by eso View Post
    Physical Graffiti is one of their better mixed records. Start out with Custard Pie...
    Will do.

    Not sure which version I have, but that album has been released multiple times and probably remastered each time. There was a time when I thought that was a good thing..

  15. #15
    Senior Member DerekTheGreat's Avatar
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    Oh yeah, that was a good show. I think In My Time of Dying and Black Country Woman were most memorable. Thank you for the suggestion! I haven't jammed that album since high school, was good to relive it.

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