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Thread: NEW 1.5 inch horn for 4345 / 4343

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    RE: Member when? subwoof's Avatar
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    NEW 1.5 inch horn for 4345 / 4343

    Ok - here's the situation.

    JBL designed the large studio monitors back when all that was available were:

    (A) The small format ( 2420/21 and 2425 ) 1.75" coil diaphram that had a 3 bolt 1" exit.
    (B) The large format ( 2440/41 and 2445 ) 4.0" coil diaphram that had a 4 bolt 2" exit.

    However since then the newer 1.5" format drivers ( with both the 3" and 4" coils ) have been introduced and they are capable of *significant* advantages in response, distortion, power and of course, weight.

    So it sounds like a good idea to stick them in the 4343 and 4345's to improve the critical upper midrange.

    The additional benefits are:

    (I) Much shorter length from phase plug to lens ( the 1.5" drivers have NO integral horn )

    (II) Newer diaphram materials ( beryllium and Coated titanium ) along with newer geometry aluminum AND improved adhesives.

    (III) Newer Magnetic material that reduce the weight from 1/3 to 1/10 of the original !!

    (IV) Newer phase plug geometry that reduces cancellation and distortion - much smoother response

    **But**

    JBL did not make a compatible horn that fit these new drivers that could be retrofitted into the older monitors. The only way to do this was to get a pair of 2311's ( good luck ) AND a pair of 2330's ( good luck X5 ) and redrill the 2330 to accept the new driver. And even when this is done the horn length is still appox 7" ( see table below )

    So, with a little determination, a pair of sacrificial 2307's and basic power tools, we created a new horn that fits the old monitors and is only 4.75" long.

    The process was straight foward:

    (1) Built a jig that allowed a standard bandsaw ( with a metal cutting blade ) to lop off the original flange and some of the horn.

    (2) Cut the new flanges from 3/4 Baltic Birch plywood ( 5.75" dia ) with a router circle cutting jig.

    (3) Bore a 1.5" hole in the center with a $$ forstner bit *** USE A DRILL PRESS ***

    (4) Rabbet a recess to allow the horn to fit into - dimensions on drawing are appox. ( the castings were a little different )

    (5) Drill mounting holes with forstner bit on drill press - Note that 2 radiuses are used ( 8 holes total )

    (6) Clean surfaces and remove old paint from horn.

    (7) Assemble the parts with fiberglas resin and put 1/8 nylon rope into the gaps.

    (8) Sand, primer with rustoleum 7220 and paint with 7769 texture black paint.


    Actual horn length table:

    2307 / 2421 is 10 1/2 " ( 8 1/2 + 2 )
    2311 / 2441 is 7 1/2" ( 4 3/4 + 2 3/4 )
    2313 / 2451 or 2435 is only 4 3/4"

    The final product worked out well and I hope to have them in the 4345's this weekend with the new 2435 drivers.

    Next project will be routing a horn sub baffle into the 4345 to allow multiple horn combinations with individual panels ( based on the 2332 cutout )

    sub.
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    Last edited by subwoof; 04-05-2004 at 08:55 PM.

  2. #2
    RE: Member when? subwoof's Avatar
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    The Jig

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    RE: Member when? subwoof's Avatar
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    The 2307 after cut off:

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    RE: Member when? subwoof's Avatar
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    The new wood flanges:

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    RE: Member when? subwoof's Avatar
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    The new flanges all routed + drilled. The horns prepped for assembly:

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    RE: Member when? subwoof's Avatar
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    Assembled:

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    RE: Member when? subwoof's Avatar
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    Sanded + finished:

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    RE: Member when? subwoof's Avatar
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    Comparing the 3 horns:

    L to R:

    2307 ( 1" exit )
    2313 ( 1.5" exit )
    2311 ( 2 inch )

    Note that the overall depth of the 2311 and 2313 is the same.
    Last edited by subwoof; 04-05-2004 at 08:57 PM.

  9. #9
    Dang. Amateur speakerdave's Avatar
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    Boy, subwoof, when you answer a question you don't fool around!

    That's a very crafty job of work--thanks for sharing it.

    David

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    RE: Member when? subwoof's Avatar
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    Well giskard the *next* batch will be with welded aluminum flanges and I will have a machine shop make up a bunch....

    In the process of test fitting these in the 4345's ( along with many horn/driver combo's ) I found that the larger diameter 1.5" ( 2451 ) and 2" ( 2450 / 475 / 2441 ) WILL fit with the 2311 horn.

    BUT I don't think they will in the smaller 4343 ???

    It's a snug fit but it's possible that some production runs might be different???? I have seen some pretty poor craftsmanship / tolerances in some of the cabinetry from that era....


    sub

  11. #11
    Senior Member herve M's Avatar
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    good good !!!
    the exponential horn is the best ! Aperture, warm, fine sound.
    The biradial horn is superior for imaging, but the sound is sad and weak.
    Vote for exponential horn resurrection !!!
    HervéM

  12. #12
    Senior Member herve M's Avatar
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    HI hi hi!!
    Memory memory:
    Ian McKenzie 2344a out !
    (general: 2344a versus 2307/2308+2405)

    and monitor preference poll (05-2003): 434x: 45% and 433x 15%
    and 4430 20%.

    and me: 2344 PAIR IN CARTON: to be sold.

  13. #13
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Originally posted by subwoof
    In the process of test fitting these in the 4345's ... I found that the larger diameter ... 2" ( 2450 / 475 / 2441 ) WILL fit with the 2311 horn.
    Hey, sub...

    Very impressive work, and smart thinking!

    A question: I scoped-out the 2441 / 2311 possibility for my 4345's and the motor diameter was too large to fit - it would take modifying (I thought...) the rear/top of the 2122 doghouse for the fit. Not true?
    bo

    "Indeed, not!!"

  14. #14
    Administrator Mr. Widget's Avatar
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    Originally posted by Giskard
    Only if you have hearing damage my friend
    I can see going back to the exponentials in my Senior Citizen years.

    Yeah Baby!
    Hey silly rabbit, exponential horns are for kids!


    Widget

  15. #15
    Senior Member Ian Mackenzie's Avatar
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    Lager.....Na na Victoria Bitter or Guinness thankyou...Fosters makes me Fart...hang on so does Giuinness....whatever


    Hey Subwoofer,


    Might have to book an audition.....around 12 to 20 May if possible

    An invite please.

    Ian

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