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Thread: 4345 monitor plans

  1. #46
    Senior Seņor boputnam's Avatar
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    2122 MF is not centered within the subenclosure

    For any interested, Ian and I have beem emailing on whether the MF 2122 is centered, or off-set, within the "doghouse" subenclosure. I think we have sorted the mystery, but I will make confirmatory measurements this weekend. Here is an excerpt from an email to Ian:

    *****

    Hey, Ian...

    Your logic appears spot-on. But, I have attached a more compelling picture, and perhaps better guesstimate to your question. This view is looking into the baffle-cut for the 2245H, up toward the doghouse. The 2245H is centered in the baffle, as you know.

    The perspective is disorienting, but the view is from the base of the cabinet upwards into the cabinet body. This is of the RH cabinet, thus the ports are on the right. The vertical bracing holding the network is centered on the cabinet back, and thus, so is the 2122 doghouse.

    The baffle width (measured inside the molding) is 28 inches wide.

    Therefore, using the LH cabinet (where all the photos with the measure tape are collected), since the 2245H is centered, but the 2122 and 2421B are aligned but off mid-line (to the right in LH cabinet), and the approx. center of the 2122 is 17-in from baffle left edge (see relevant view on this Thread), versus baffle vertical mid-line at 14-in from baffle left edge, the 2122H is exactly 3-in "inside", or to the right of the mid-line (3-in right of mid-line in the LH cabinet, and 3-in left of mid-line in the RH cabinet). Thus, the 2122 is not centered within the doghouse.

    Make sense?
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    Last edited by boputnam; 08-28-2003 at 07:10 AM.
    bo

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  2. #47
    Senior Seņor boputnam's Avatar
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    Same-same in 4343's...?

    Looking at some photos of 4343's, I wonder whether the 2121 MF is mounted above subenclosure center point, for the same reason.

    But, I'm (again...) out on a limb, here...
    bo

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  3. #48
    Senior Seņor boputnam's Avatar
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    The end...

    For completeness, here is a shot through the rear access panel. The 2421B is removed, so you can see through, out my window to the neighbors...

    The 2307 is mounted to the baffle, and the 2421B motor is held by a bracket that bolts to the motor-horn join, and then wood-screws into the back of the 2122H subenclosure.

    So, I think that's it.

    Any questions, post 'em or pm 'em. Good Luck!

    Class, dismissed...
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    bo

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  4. #49
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    Bo,

    You never told us your 4345s (she) has rear entry for easy access.

    Got any more tricks Bo!!

    Mind you how else would one be able to service the drivers.

    Ian

  5. #50
    Senior Seņor boputnam's Avatar
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    Originally posted by Ian Mackenzie
    You never told us your 4345s (she) has rear entry for easy access.
    Why, I thought everybody knew that!

    That is the boot of the 4345. Where do you think we store all those illicit recone kits?
    bo

    "Indeed, not!!"

  6. #51
    Senior Seņor boputnam's Avatar
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    The thread that started it all...

    Hey, Ian...

    I thought I'd better tag a reply to this long-ago Thread - there's quite a few dimensions and such you hassled me through (damned Aussie...) and maybe some of the newer fans haven't-yet stumbled this far into our collective past...

    bo

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  7. #52
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    You are entirely correct Bo,

    My error.


    One of the problems is that unlesss we use stickies, many of our valuable threads disappear, and are only visible to new users for 30 days...as I understand it.

    Perhaps we can twist Dons arm and move this and the build thread into a special area

    Ian

    Well we better get qualification on that, Don mentioned as much in conversation the other day.
    Last edited by Ian Mackenzie; 03-15-2004 at 05:33 AM.

  8. #53
    Obsolete
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    Wow, I guess I didn't know that. I've sure been wasting time posting on this forum. No wonder the same old shit keeps coming up over and over again.

  9. #54
    Senior Seņor boputnam's Avatar
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    Yea, that is in-part why I've adopted the Try the Search Button (you dope... ) mantra. It is an amazingly powerful tool, even on so poorly organized a database as is this.

    And, that has encourged me to properly label all posts - particularly when there is only an image being posted. Without a label, that image is unattributed (not tagged) and is lost to the ether...
    Last edited by boputnam; 03-15-2004 at 08:31 AM.
    bo

    "Indeed, not!!"

  10. #55
    Senior Member maxwedge's Avatar
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    Originally posted by Giskard
    Wow, I guess I didn't know that. I've sure been wasting time posting on this forum. No wonder the same old shit keeps coming up over and over again.
    Your time's not wasted. I just wish you wouldn't be so quick on the delete key.

  11. #56
    Senior Seņor boputnam's Avatar
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    Question Different slopes, passive and active...?

    Hey, Giskard...

    Stumbling around last night, I discovered (loosely used...) that while the active 5234A and passive 3145 networks both crossover at 290Hz, the 5234A uses an 18dB slope, while the internal passive 3145 uses 12dB.

    I apologize if we (or you all...) covered this before, but wonder why the passive was not engineered with the same slope as the "preferred" bi-amp active option...?
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    bo

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  12. #57
    Administrator Mr. Widget's Avatar
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    Bo,

    I believe JBL used the 18dB card to build a tweaked 12dB circuit for the 51-5145. I believe this "tweaked" crossover was to correct for the upper bass bloom that I discovered in my earlier 4355 experiments.

    Widget

  13. #58
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    I have recently looked at this odd thing myself.

    The 51 5145 card values are a standard 18/18 slope 290 hertz curve. Giskard has modelled that more me recently while I have been quietly developing a more current active network for the 4345/4344 system down here in the deep dark southern hemisphere.....with an Americana Pizza thrown in for good measure. Just waiting on some special juicy parts.

    More enlightening however is comment from Greg Timbers:

    "Bi-amping, bypassing the input inductor, almost always gives better and tighter bass performance. However, most electronic crossovers have fixed crossover slopes and shapes and our passive crossovers are custom tailored for the response of the specific drivers used. This usually results in more precise acoustic drive parameters. You will note that the specifications call for 290 Hz for the electronic crossover and the passive one is 320 Hz. This was done to get the best response possible from off the shelf electronic curve shapes.
    The bottom line is that an electronic crossover on this system probably will sound better than the internal passive, but it is a bunch of extra parts and trouble. "

    So, there you have it.

    That email is now taken pride and place among others in my Audio Hall of Fame.

    I can't wait to commune with Bo's 4345's .

    cheers

    Ian
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    Last edited by Ian Mackenzie; 04-09-2004 at 02:17 AM.

  14. #59
    Senior Member 4345's Avatar
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    alnico and ferrite

    Bo,

    So, your 4345's have a 2421b(alnico) and 2405h(ferrite). I would have thought both would be alnico. Do you think it was done at the factory like that?

  15. #60
    RE: Member when? subwoof's Avatar
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    4345 magent types

    Mine have alnico 2405's and 2421B's but the network / cabinetry is the same as bo's.

    Another cool option for biamping is the urei ( pre jbl ) 525 crossover. Since it has 18db slopes, it can be precisely adjusted to 290hz via the front panel frequency counter which actually measures the resonant freq of the crossover point by making it feedback ( ring ) slightly when the momentary switch is engaged.

    And if you use in in stereo 3 way mode, and change the first 2 section's filter caps to 2X the original, you can use those as HP filters down to 20hz.

    The internal output buffers and xformers can be ignored and the signal picked off earlier for those who fear iron and class B....



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