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Thread: Oh no. I did it. JBL 4520 related

  1. #61
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    Circumference of What?

    Quote Originally Posted by Lee in Montreal View Post
    Some horn principles call for the mouth circumference being the length (or period) of the lowest wave length reproduced. The mouth above is .95m x .69m or 3.28m in circumference.
    The recommendation that the mouth circumference should be one wavelength is meant for a circular mouth of equivalent area.

    ruediger

  2. #62
    Senior Member Eaulive's Avatar
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    Quote Originally Posted by Lee in Montreal View Post
    Looking at the third picture, I can see some writing on the walls. "Sortie", "Entrée". I guess the cabinets and drivers must have been assembled in Montreal for a local bar. "Stereo" in Montreal had 8 of them, standing on Berthas with Levan horns. But that bar was set-up by SystemByShorty, not GSA. I wonder what bar has those tall cabinets in Montreal...
    Good eye, is that company local?

  3. #63
    Senior Member Eaulive's Avatar
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    Nope, I just googled them...Las Vegas.
    http://www.gsany.com/

  4. #64
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by Eaulive View Post
    Good eye, is that company local?
    GSA is from NY, but cabinets and drivers must have been assembled in Québec for a local bar.

    And they are definitely not the ones at "Stereo". They had regular 4520s and Berthas with Levan extensions.

    http://www.systemsbyshorty.com/sbsstereo1.swf

    And found this interesting thread with Shorty himself.
    http://www.wavemusic.com/community/s...ad.php?p=45333

  5. #65
    Senior Member Eaulive's Avatar
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    On the last pictures, I don't recognize the city, and it's definitely not Montreal!
    Unless the mountain vanished....

  6. #66
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    Quote Originally Posted by Lee in Montreal View Post
    Picked mine this morning with Eaulive and Stéphane. Out went the 4530s and in came the 4520s. Spent a few hours sanding and fixing on of the 4520s. Now the paint is drying in my basement. Those things are huge compared to a 4530. . 7" taller, 6" deeper, 12" wider.

    Attachment 50536
    Nice set-up! What Behringer EQ model is that?

  7. #67
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by JBL 4645 View Post
    Nice set-up! What Behringer EQ model is that?
    This one is a CX3400 and love it. I also have a DCX2496.

  8. #68
    JBL 4645
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    Quote Originally Posted by Lee in Montreal View Post
    This one is a CX3400 and love it. I also have a DCX2496.
    I noticed the DCX2496 in the other post. It’s a logical choice. I like watching the funky LED’s on mine moving up and down. Have fun with yours.

    Quote Originally Posted by Lee in Montreal View Post

    Mouth size and path length. Looking at Bertha's (simple W bins) with the Levan extension, it seems it makes sense. But don't worry. I have no intention to install Berthas in my basemement unless I want to end my couple. But damn wouldn't it be great to load them with two 2242... That sure would piss off all neighboors within a block.

    Attachment 50425
    Attachment 50426
    What are planning to do play Earthquake! You’d piss me off if that was playing below me LOL

  9. #69
    Senior Member Lee in Montreal's Avatar
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    The AJ Horn plan and the pictures from the GSA/RLA cabinets make total sense. They found the way to make the path much longer than stock 10' vs 8', even in standard height. Looks like standard 4' height gives you a reasonable 27Hz, while to achieve under 25Hz, the cabinet must definitely be much taller to accomodate a bigger mouth and longer path. I guess I will settle with 27Hz.

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  10. #70
    Senior Member Lee in Montreal's Avatar
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    Found some interesting reading.

    http://www.ibiza-voice.com/media/new...van/sound.html

    "The first part of the new system consisted of 4 "Waldorf" bass speakers. First used in a rental at the Waldorf Astoria, it is similar to the JBL double 15" scoop enclosure but is based on the old Jensen Imperial design. The enclosure was made larger to accommodate a larger rear loaded horn, which was designed with a hyperbolic rather than an exponential flare. The high end consisted of the largest JBL horn lens for smooth wide dispersion and the system is electronically crossed over at 80hrz These replaced the corner home-type speakers."

    Leading me to that http://www.decware.com/imperial.htm
    "High Fidelity Playback - As shown above with special considerations or with a single 15 inch coax, using the 2nd woofer for 50 Hz and below."


    Basically, despite the ressemblance with a 4520, the Waldorf, as designed by Richard Long, is an "adapted" Jensen Imperial. I still wonder how they made the cabinet go down in frequency if the tunnel is that short. BTW GSA's cabinets seem to be the same as RLA's as he was transfered the technology after Ricjard Long passed away. From the pictures I posted a bit earlier, the front view shows a deep recess behind the drivers, and the upper "ducts" as on the Jensen Imperial.


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  11. #71
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    [QUOTE=Lee in Montreal;310387Then this summer I will build the 4520s for 18" 2240h drivers. Found a place in the US where they have them for $125 a piece with recent original JBL recones.
    Lee[/QUOTE]

    You can do other fun stuff with 2240: Diy 80hz mid-bass horn... drums never sounded so good!

  12. #72
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by more10 View Post
    You can do other fun stuff with 2240: Diy 80hz mid-bass horn... drums never sounded so good!
    I am close to finishing the design of the cabinets. Unlike the Waldorfs which seem to have a large back chamber (which is supposedly good for round bass), I am electing to use a small back chamber to promote compression and efficiency. The goal is to have a tight/fast bass (like a 4530) but down to 30Hz. The cabinet will be 5' tall and 30" deep. Still manageable at home.

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  13. #73
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    doesn't work that way

    Quote Originally Posted by Lee in Montreal View Post
    ...
    I am electing to use a small back chamber to promote compression and efficiency. The goal is to have a tight/fast bass (like a 4530) but down to 30Hz.
    ...
    The backchamber acts as a low pass filter at the entrance to the horn. At, say, 150Hz+ it shall prevent sound waves from entering the horn, as that would lead to destructive interference together with the sound radiated from the front of the speaker.

    ruediger

  14. #74
    Senior Member Lee in Montreal's Avatar
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    According to DB Keele, one of the way to calculate the back chamber in a rear horn loaded bass cabinet is the formula below. It is one of the ways as not everyone seems to agree.
    • VB is the back volume (volume of compression chamber)
    • ST is the throat area of the horn (590cm2)
    • FC is the horn cutoff frequency (30Hz in my case)
    • c is the velocity of sound (344m/s)

    My calculations tell me I need 0.1076m3 volume. The volume can be reduced by lowering the thoat area, or raising the cut-off frequency.

  15. #75
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    Don't think so

    Quote Originally Posted by Lee in Montreal View Post
    That is equation 14 from the Keele paper. It is about front loaded horns, not about rear loaded ones, or am I missing something?

    Ruediger

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