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Thread: Building the 4345/4344

  1. #46
    Administrator Robh3606's Avatar
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    Hello David

    I run an all active set-up because I am weak with passives. I realized early on how difficult it was to get it really right on your own. I like to try new drivers and fiddling and voiceing a passive crossover is an art. That said if you are clonning an existing system and you have the crossover schematic there is no reason not to give it a go. You have a baseline, it is a great learning experience and its fun if you like to tinker. I will also be building up a pair and in this case I will be using the JBL designed crossovers.

    Rob

  2. #47
    Senior Member andresohc's Avatar
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    3145 components list, board layout?

    Ian, I am attempting to build the 4345 (probably mostly inspired by your posts) and wondered if you have posted somewhere the parts list for your system (the crossover components you purchased, your board layout, your actual speaker elements you are using, whether you modified the crossover significantly from the original JBL circuit, if so your schematic) Any direction to the posts would be great. Thanks for taking the time to document and post all this.

  3. #48
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    What,

    Another one comin out of the wood work.....LOL.

    Okay,

    I will cook up a list shortly...have you already built the cabinets?

    Looks like another JBL weekend coming up...LOL

    Ian

  4. #49
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    Here is the first of a series of line drawings for making the 4344 enclosure. The simplified drawing below shows the overall baffle dimensions, cut-out centres and cut out diameters.

    I based this layout on the 4345 with consideration of the smaller 15 inch 2235 driver.

    Some detailed discussion is in order.

    The overall baffle height is almost identical to the 4345 and the exterior dimensions account for a 1/4 routered section into the top and sides.

    As you can see the woofer has been pushed over in line with the midrange and horn to minimise standing waves that may otherwise occur with equidistant placement with the adjacent side walls and the ports positioned beside the woofer.

    The level pads are repositioned below the 2405 which has also been raised a little in accordance with the 4344 layout. To compensate for the size of the15 inch 2235 driver in the lower baffle region the overall position of the driver set has been lowered an inch to give balance to the layout. Thus the modified position of 2405 retains perfect ear height for its vertical dispersion.

    This drawing is rev0.00 and I anticipate discussion from you guys after which it can revised. If some wishes to tart up the final revison with a Cad package that would be nice.

    I will post the other drawings in a day or two.
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    Last edited by Ian Mackenzie; 03-13-2004 at 02:33 AM.

  5. #50
    Senior Member jarrods's Avatar
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    Hi Ian,

    Could you please elaborate on the 1/4" routered you mention.

    Also I take it from various posts I have seen on the forum, and your comments above, that this type of off centre mounting of the 15" is better sonically than the central placement as in the 4434 MkII. (Could the rational of centralizing it in that model based on aesthetics??? - surely not!)

    thx jarrod

  6. #51
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    Okay,

    The baffle has to fix to somthing or it will fall out.

    This can be done several ways but the most elegant solution and the one JBL uses is to router / rebate a channel all the way around and inset to the sides/top/bottom the thickness of the front baffle. Side stiffeners the full depth of the enclosures finshe the job.

    The effect is strong and rigid structure which will also be square when the cabinet is assembled.

    Regards the reason for the woofer being off centre, standings wave are the issue causing potential response peaks/dips.



    Ian
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  7. #52
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    "Could the rational of centralizing it in that model based on aesthetics??? - surely not!"

    Absolutely! Numerous JBL systems were based on that rational.

  8. #53
    Senior Member jarrods's Avatar
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    OK, got it.

    I was going to make the back recessed in like that but have the baffle screwed on to a recessed bead to allow access into the box.

    I see in the exploded view posted of a 4343 that JBL fit the back recessed, the lower bass driver baffle recessed, but the top mid/high baffle is not recessed and appears to be screwed to a 25x18mm bead that is recessed. I may adapt this composite idea to my 4344, but then you see screw heads from the front.

    -jarrod

  9. #54
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    Originally posted by jarrods
    OK, got it.

    I was going to make the back recessed in like that but have the baffle screwed on to a recessed bead to allow access into the box.

    I see in the exploded view posted of a 4343 that JBL fit the back recessed, the lower bass driver baffle recessed, but the top mid/high baffle is not recessed and appears to be screwed to a 25x18mm bead that is recessed. I may adapt this composite idea to my 4344, but then you see screw heads from the front.

    -jarrod

    Jarrod,

    I sense you are eager to get started...... all will become clear shortly...... best not to rush as this project is much bigger than it looks and mistakes can be hard to undo.

    Regards the access, it is planned that the upper portion of the rear panel be removeable for servicing of the HF and UHF drivers.

    The 4343 front panel for the mid, HF and UHF was made to be rotated for side mounting if required. I doubt if this feature is necessary or desireable for home listening.

    Whole removeable panels are not recommended and unnecessary; fitting them up to be removeable is often less than neat in appearance, yes the screws will show and screws and holes tend to shear, leaks are more likely to happen. If all the drivers are removable why have removeable baffles.....

    I will post the side elevation tomorrow night with all internal dimensions.

  10. #55
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    Re: 3145 components list, board layout?

    Originally posted by andresohc
    Ian, I am attempting to build the 4345 (probably mostly inspired by your posts) and wondered if you have posted somewhere the parts list for your system (the crossover components you purchased, your board layout, your actual speaker elements you are using, whether you modified the crossover significantly from the original JBL circuit, if so your schematic) Any direction to the posts would be great. Thanks for taking the time to document and post all this.
    Okay,

    Drivers:

    2245H
    2122H
    2420 with 2425 diaphram
    2405 Alnico

    Crossover: The schematic is available from the jblpro.com


    http://www.jblproservice.com/pdf/Net...%20Network.pdf

    chokes

    5.4 mh dcr 0.5 ohms
    4.8 mh dcr unknown (or as above)
    1.8 mh dcr unknown

    Notes
    JBL used iron core chokes to miniimise losses here but you can use air core which in theory are better but more costly. The 5.4 mh chokes JBL used had a dcr of 0.5 ohms for production reasons, you can shoot for a lower dcr but some retuning of the 2245 ports may be required according to Greg Timbers.

    In my crossover the tapped chokes were not used (as they are unavailable to the best of my knowledge) and an alternative consisting of split air core chokes provides equivelant voltage drive. (courtesy of Giskard/GT)

    0.68 mh/ 0.32 mh HF section

    0.122 / 0.05 mh UHF section

    I wound these values by trimming commercial standard values with an LCR meter. I am happy to provide these chokes for a small fee if you are unable to arrange this.

    I will post a pdf of the equivelant circuit for the HF and UHF section shorlty. (Note the 0.24 hm choke is not used in the equivelant design)

    I had the large chokes made to order, if you live in Australia Voller Transformers are excellent, if you are in the USA try Parts Express , SpeakerCity, Zalytron and others on www and if you are in Europe try Mundorf.

    Capacitors.

    This has to be the most debated area of DIY Audio. I will avoid any discuss as I am sure you will have fun tweaking the sound to your liking.

    90 uf 250 VDC*
    60 uf 250 VDC*
    20 uf 250 VDC*
    14 uf 250 VDC*
    8 uf 100 VDC#
    3 uf 100 VDC#
    12 uf 100 VDC#
    1.5uf 100 VDC#
    1.0uf 100 DVC#

    *I used metalised polypropolyene non polorised capacitors here, sourced from AOEN, bypassed with 0.1 uf film foil AEON.
    # These are all Hovlands speaker capacitors.

    #I highly recommend pure film and foil varieties in this design. They are expensive but the results show. Try PartsConnexion, Handmade Electronics, Welbourne Labs and the diy speaker supplier mentioned above.

    You can of course use metalised polypropolyene or mylar and bypass with small film foils capacitors. JBL did this in the original design. I recommend North Creek Audio as a supplier for this approach.

    Resisters

    25 ohm 10 watt
    5.1/5.1 ohm 10 watt
    39/39 ohm 10 watt
    62/62/62 ohm 10 watt
    20 ohm 20 watt
    39/39 ohm 10 watt

    I recommend Mills power resisters here, the ceramic resisters and usable but they are very fragile.

    The pads are all ( 3 ) x 8 ohm 50 watt, they can be sourced from Parts Express.

    The layout I used was done with Tag Stripes and point to point, not on a PCB. I will post this when time permits

    Ian

  11. #56
    Claus K
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    Hi Ian,

    can you tell us how the split of these inductors is. I mean would the smaller inductors form the bottom or on the top half sections?

    Another idea I have is instead of using split inductors to use normal inductors of the full value (e.g. 1mH for the HF part) and then carefully unwind them measuring remaining inductance until you´ve reached the required "split point", then scratch off some of the wire isolation and solder a "tap" wire onto the inductor wire. Then rewind the wire that you wound off again. Basically you would end up with a kind of DYI tapped inductor.

    Using two separate inductors as you suggest will give the same voltage drive but with a higher source impedance and I´m pretty sure that this will change the crossover characteristics (mabe the change is small enough though).

  12. #57
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    I did not model the equivelant on Spice, but can assure its measures precisely.

    Ian
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  13. #58
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    The HF network

    Ian
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  14. #59
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    The layout....I just followed the schematic

    Ian
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  15. #60
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    Please refer to this thread 4345 Monitor plans for full visual exterior dimensions...courtesy of Bo.

    http://audioheritage.csdco.com/vbull...7518#post17518

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