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

  1. #46
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by Eaulive View Post
    Don't think so either, VC won't fit in the gap.
    So it must be something else that fits in but doesn't sound right.

  2. #47
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    Quote Originally Posted by Lee in Montreal View Post
    Then this summer I will build the 4520s for 18" 2240h drivers.
    Why don't you build new Rog Mogale 18" cabinets instead of modifying the 4520s?

    PD1850:
    THIELE SMALL PARAMETERS
    Fs 30 Hz
    Re 5.4 Ohms
    Qts 0.21
    Qms 6.04
    Qes 0.22
    Vas 249 Litres
    Mms 216.4 g
    Sd 1150 cm2
    Cms 133 μM/N
    BL 31.57 T/m
    Xmax 11.05 mm
    Vd 1.271 Litres
    Reference Effi ciency 2.88 %

    2240HG:
    Thiele-Small Parameters:
    fs: 30 Hz
    Re: 6.0 ohms (H); 2.5 ohms (G)
    Qts: 0.23
    Oms: 2.2
    Qes: 0.25
    Vas: 480 I (I7 ft’)
    SD: 0.130 m2 (200 in’)
    X max: 5.5 mm (0.22 in)
    VD: 720 cm? (44 in?)
    Le: I.4 mH (H); .65 mH (C)
    q. (Half space): 5.0%
    Pe(Max): 300 W Continuous Sine Wave

    They differ in Qms and Vas. I have no idea if it is going to work well.

  3. #48
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by more10 View Post
    Why don't you build new Rog Mogale 18" cabinets instead of modifying the 4520s?
    Because the Superscooper is a modified 4530 (single driver) and I am using two drivers per enclosure (4520).The 4520 and 4530 sound very differently. One is a kick bin (4530) while the other goes deeper (4520).

    The Superscooper has a 2.22m pathway, while the 4520 I redesigned has 2.57m, and a lot more volume. Longer pathway and extra volume = deeper bass.

    If I made the enclosure 4" taller, I could increase the pathway by 11" and reach 30Hz.

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  4. #49
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    If You insist on scoops ...

    Quote Originally Posted by Lee in Montreal View Post
    Because the Superscooper is a modified 4530 (single driver) and I am using two drivers per enclosure (4520).The 4520 and 4530 sound very differently. One is a kick bin (4530) while the other goes deeper (4520).

    The Superscooper has a 2.22m pathway, while the 4520 I redesigned has 2.57m, and a lot more volume. Longer pathway and extra volume = deeper bass.

    Attachment 50794
    1.) You may scale the 4530 linearly by multiplying height and depth coordinates with a constant factor.

    2.) Why not build 4 single scoops instead of 2 double scoops? Would be easier to transport.

    3.) Have a look at
    http://www.audioheritage.org/vbullet...500&viewfull=1

    ruediger

  5. #50
    Senior Member Lee in Montreal's Avatar
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    I will read the whole thread tonight. But something tells me I am heading in the right direction.

    http://www.audioheritage.org/vbullet...ll=1#post34779

    "Originally the E-155-8 is what we used in our upsized JBL copies! They were great, the punch, the bass articualtion, and fast transient snap were fantastic! But wasnt the greatest deep bass! The 2240 makes better deeper bottom!..."

    "On an RTA I have usable response down to 30Hz, it actually is flat down to 30, and I can squeeze some response to 25hz..."

  6. #51
    Senior Member Lee in Montreal's Avatar
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    I have quickly redesigned and simplified the AJ Design principle (adding one baffle to extend the pathway) that was mentionned in that old thread. The bin has the same height and depth as a stock 4520, only a few inches wider to accomodate a pair of 18" drivers in replacement of the original 15".

    There not much to change as it is. It is tuned to the 2240h's Fs 30hz.

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  7. #52
    Senior Member Eaulive's Avatar
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    Yes , I saw this design also but the LF cutoff is determined by the mouth area if I'm not mistaken so no gain here.

  8. #53
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by Eaulive View Post
    Yes , I saw this design also but the LF cutoff is determined by the mouth area if I'm not mistaken so no gain here.
    If the cut off was only determined by the mouth, then I would probably simply cut a big square hole in a 4'x8' and place a woofer behind... Just kidding.

    Transmision lines speaker and tapped horns are closely related to the length of the pathway, which is what determnes the resonance. I might be wrong, but isn't mouth size only one of the elements that determine how low the cabinet can go?

  9. #54
    Senior Member Eaulive's Avatar
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    Quote Originally Posted by Lee in Montreal View Post
    If the cut off was only determined by the mouth, then I would probably simply cut a big square hole in a 4'x8' and place a woofer behind... Just kidding.

    Transmision lines speaker and tapped horns are closely related to the length of the pathway, which is what determnes the resonance. I might be wrong, but isn't mouth size only one of the elements that determine how low the cabinet can go?
    I think it's one of the elements, yes, not the only one probably, but nevertheless, if one of the elements limits the cutoff, there's no point in optimizing the others to go lower.

    That's my understanding, I may be wrong.

  10. #55
    Senior Member Lee in Montreal's Avatar
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    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.

    According to the principle previously mentionned, this should be good for 104hz... I understand that 4520s go much lower than that. Therefore I suspect that the principle that works for midrange horns might not apply necessarely to a bass horn as otherwise 30Hz, would require a 10.5 square meter mouth according to this other calculation.

    SL = (c / (2 fc))2 / π

    C is speed of sound
    Fc is frequency cut-off
    π is 3.1415.....

  11. #56
    Senior Member 1audiohack's Avatar
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    [QUOTE=Lee in Montreal;310474]Some horn principles call for the mouth circumference being the length (or period) of the lowest wave length reproduced. [QUOTE]

    One wave length if operated in free space, sat on a plane you get to halve the mouth arra as the boundary is seen by the driver/horn assembly as another like unit, pushed up to a side wall and you get to halve the mouth area again. The type of unit you are building does not lend itself to eighth space loading so the party ends at 1/4 space, 25% mouth area.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  12. #57
    Senior Member Lee in Montreal's Avatar
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    Quote Originally Posted by 1audiohack View Post
    The type of unit you are building does not lend itself to eighth space loading so the party ends at 1/4 space, 25% mouth area.
    If indeed the principle to follow is that the circumference shall be 1/4 wavelength of the lowest frequency, then 3.28 meters (the throat perimeter) is good for 26Hz. Good enough for a pair of 2240 woofers with Fs = 30Hz and a pathway tuned to 29Hz (maybe 30Hz).

  13. #58
    Senior Member Lee in Montreal's Avatar
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    For those with no space limitation, i found that Gary Stewart Audio is making what looks like his own brew of Waldorf. Talk about a big mouth... They seem to be based on the JA Horn with the extra vertical baffle.

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    And a single driver version

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  14. #59
    Senior Member Eaulive's Avatar
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    Big!

  15. #60
    Senior Member Lee in Montreal's Avatar
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    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...

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