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Thread: Are these Genuine JBL Diaphrahms 2403/076

  1. #1
    Senior Member cjwebber's Avatar
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    Are these Genuine JBL Diaphrahms 2403/076

    Would someone be able to tell via this picture whether these diaphragms are genuine?

    These are on a pair of 2403s
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    Senior Member jblwolf's Avatar
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    very questionable replacements had inspector stamps and dates of manufacture.originals Ive seen have had a red dot on brass finish,that said they may not be the original mags.

  3. #3
    Senior Member ivica's Avatar
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    Quote Originally Posted by cjwebber View Post
    Would someone be able to tell via this picture whether these diaphragms are genuine?

    These are on a pair of 2403s
    Hi cjwebber,

    It seems to me that they are genuine diaphragms...
    but the F/R measurements would give You real answer.


  4. #4
    RE: Member when? subwoof's Avatar
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    I bought ( and sold stupid cheap alas ) 40 2403's ( pro 076 ) from a texas SR company many years ago - one thing that stood out was that the diaphrams had the silver outside aluminum gasket but it was BLUE under the phase plug....

    All the other dia's in my collection had matching colors.

    Remove the phase plug and see...!

  5. #5
    Senior Member ivica's Avatar
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    Quote Originally Posted by subwoof View Post
    I bought ( and sold stupid cheap alas ) 40 2403's ( pro 076 ) from a texas SR company many years ago - one thing that stood out was that the diaphrams had the silver outside aluminum gasket but it was BLUE under the phase plug....

    All the other dia's in my collection had matching colors.

    Remove the phase plug and see...!

    I think that at the beginning only "silver" inner and outside rings were used, then ( when 077) a blue rings become, but today all ring are 'golden colored'.
    from some posts here I have collected some words about 2402/3/4/5 ( 075/6/7):
    Ring Radiator Comparisons

    This thread will show the on and off axis response of all four of JBL's ring radiator tweeters. There seems to be some confusion over these so here is a mini background. All four tweeters can use the same diaphragms and have the same motor structure. There is an alnico and ferrite version. After having measured several of each tweeter in both motor types I am certain that there is a fair amount of unit to unit variation, but not due to magnet type.

    The first model of this series was the 075 "Bullet Tweeter". There is also the Pro variant the 2402 and the ferrite version, the 2402H. This model has a the heaviest diaphragm of the three and is capable of operating over the widest frequency range. It also has the most focused dispersion pattern.

    The next model offered was the 077 "Slot Tweeter" and it's Pro variant, the 2405. Later there was the ferrite 2405H. This model has the lightest diaphragm and offers the widest dispersion pattern and produces the highest frequencies.

    The third model offered by JBL was the 076. There was also a Pro variant offered, the 2403 in alnico and the 2403H in ferrite. It was originally designed specifically for the L220. It uses a unique diaphragm. I believe that it has a moving mass that is between the 075 and 077.

    The final model offered by JBL was the 2404H. It uses a mini butt cheek bi-radial horn. It uses the 2405 diaphragm, but is usable down to much lower frequencies than the 2405.

    075/2402, 076/2403, 2404, 077/2405

    All three diaphragm kits D8R075, D8R076, and D16R2405 use the same voice coil part number.

    (All three diaphragms have the same DCR specification regardless of any D8R versus D16R assembly number prefix. Actual transducer impedance will vary depending on diaphragm loading.)

    Both D16R2405 and D8R075 use the same diaphragm part number. D8R076 uses a different diaphragm (dimensions).
    All three kits use the same raw diaphragm material (.002 inch thick Aluminum).
    There are also some differences on the diaphragm spacer rings used in each kit,
    Information courtesy of JBL

    Note that the D8R076 diaphragm assembly has also been labelled D16R076 in past years.
    The only thing that I want to add is that there is a distinct difference between the AlNiCo motors and "Tops" i.e. horn parts, and the Ferrite versions of the same:

    1: The AlNiCo magnets have the guide pins, and corresponding holes in the "tops" that bolt on to the magnet assemblies.
    2: The AlNiCo magnets are smooth across the top, where the Ferrite magnets have a machined recess of approximately .015"-.017" across the face of the magnet to accept and align the diaphragm.
    3: The pole piece is aligned with the outer portion of the top plate in both the AlNiCo AND the ferrite magnets; meaning the diaphragm sits "flat" in either magnet- the diaphragms' inner clamping ring and outer clamping ring sit in the same plane on either magnet: the top of the pole piece is aligned with the diaphragm seating surface on both magnet versions.
    4: the "Tops" are machined accordingly to mate with their intended magnets: the AlNiCo magnets mate up with "tops" that have a recess for the diaphragm that is approximately .035" deep, and the ferrite magnets mate up with "tops" that have a diaphragm recess that is approximately .015"-.017" deep.

    IIRC, diaphragm clamping rings measure (thickness) approximately .040" (1mm) in all cases, I did these measurements last summer and was in regular communication with 1audiohack during the course of our measurements and other sleuthing regarding the distinctions among the various incarnations of JBL Ring Radiators.

    I measured this on my AlNiCo 075 and 2402, and compared it to a pair of 2405H as well as the magnet for a 2404H-1 that I have. I used a machinists' straightedge and feeler gauges to measure the diffeneces, and I feel confident in my findings. I believe that 1audiohack would support me on this as a viably accurate method.

    That being said, I feel that anyone concerned about "bastardized" combinations of parts could use this method to validate a proper combination...

    Additional Notes
    Since the late 50ís there have been many variations.

    Basically there is only one diaphragm (2 mils aluminum), one coil impedance, and a variety of clamp ring diameters.
    For a while, we did have a 1.6 mil diaphragm but I think those are long gone.
    There is a clamping ring on the interior and exterior of the diaphragm. This ring comes in silver and blue. The blue ones have different IDís (Inner Ringl Dia) and ODís (Outer Ring Dia) than the silver ones.
    The differences in the diaphragm assemblies come from whether the assembly has two silver, or two blue or a mix of silver and blue rings. This changes the clamping diameters and thus the stiffness of the diaphragm.

    Over the years, things have changed with the aluminum and the way the diaphragms are creased at their outer edge. This led to the different rings.

    To my knowledge, all of the motor assemblies are interchangeable from a mechanical standpoint. The ferrites probably have a little more flux level than the alnicoís but that is all. The main difference in them is the horn or bullet or whatever is mounted on the front side. Any diaphragm can go in any body. Results will vary.

    Information courtesy of JBL

    Get the right diaphragm for the application too!
    After doing a lot of research a couple of years ago here, on the JBL pro website, and anywhere else I could find (including the local JBLPRO service dealer) a couple of things became evident:

    All of the old ring radiators used the same magnet structure, except the old ones are AlNiCo and the newer ones (from about 1976 on) were ceramic-ferrite. All four designs use uniquely different phase plugs and corresponding horn throat/bell assemblies. The only other difference was the mounting flange: early ones have a round neck with a circular clamping ring to mount it to the cabinet baffle board, and the later ones had integral mounting flanges that use through-bolts to hold it on the baffle board.

    Originally, these diaphragms were made of an alloy JBL called "duralumin" in the old JBL catalogs, but that name has been dropped. Supposedly, this alloy was obtained by recycling the skins of WWII airplanes, and the supply was eventually exhausted. Newer diaphragms are referred as simply "aluminum". Different material or the same? Who knows? Some aftermarket diaphragms are made from Titanium, with uniquely different properties and sound, according to some. Those who have heard them parallel their impressions regarding the sound difference to those about JBL's dome compression drivers equipped with aluminum or Titanium diaphragms.

    JBL makes three slightly different diaphragms for these older ring radiators (075/2402 "bullet", 076/2403 "cat-eye", 2404 "baby-butt", and 077/2405 "slot") All are interchangeable, but with slightly different performance and reliability advantages.

    All of these ring radiators have the same impedance, about 12 ohms, regardless of the part number having an 8 or a 16 in it as the impedance. The same is true of the drivers- some are marked 8 ohms while others were marked 16 ohms. All the voice coils are the same.

    the D8R075 diaphragm material is apparently a little thicker. It's total effective mass is a little higher. Its HF extension is not as good as the others, but it is much more durable. It is the diaphragm of choice for high-level playback for a HP crossover frequency of 2.5-3.5KHz or higher. This is the standard replacement diaphragm for some "-1" variants of the 2404H. This is also noted on some of the exploded diagrams of certain production models that used a 2404H or a 2404H-1 The metal plate in the center and edge of the diaphragm on these are almost always golden in color.

    The D8R076 is uniquely for use in the 076/2403 "Cats-eye" tweeter. The center and outer diaphragm plate is almost always blue in color. Not much else I can say about this driver or diaphragm except that they are a cult classic JBL driver and ungodly expensive -if you can find them to buy.

    The D16R2405 is a lighter, thinner diaphragm with better HF response than the D8R075, but are more easily damaged from over-excursion and metal fatigue at high levels when crossed over lower than about 7KHz.

    Don't know if the inner and outer rings have any coloration other than silver to them at all. They are the replacement diaphragm for most 2404 "baby butt" and 2405 "slot" drivers. Exceptions include some 2404H-1 which used the D8R075. It is good recommendation to use the D16R2405 in applications from 7KHz up, and the D8R075 for applications starting above 3-3.5KHz (as in 2-way systems), with a little UHF roll off characteristics in the D8R075.

    To minimize the risk of damage and get the cleanest response, all of these really should be crossed over at a minimum slope of 12dB/octave. 24dB/oct is really much better in all ways.

    Note: be oh-so-careful not to allow the phase plug to twist even a slight amount during tightening down onto the diaphragm and magnet assembly, or the phase plug will put twisted wrinkles in the diaphragm like the tires on a drag car launching from the starting line, resulting in the death of perfectly good -and expensive to replace- diaphragm.

    This is how the JBL factory did it.

    The bottom of the phase plug is the same outside diameter, as the standard 075 / 2402, 1.720" and the "shroud" on the bottom of the phase plug is the same depth as all the 075 / 2402, 077 / 2405, 076 and 2404's (both variations) I have measured, 0.040".

    What is different is the inner flat area diameter, it is 1.450" rather than the standard 1.400" bullet. Since the outer diameter of the bullet is the same and the inner flat area diameter is different the angle of the shroud is increased to some degree.
    .......... "


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    Is this diaphragm original for 16ohm early 075?
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  7. #7
    Senior Member gibber's Avatar
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    Quote Originally Posted by script56 View Post
    Is this diaphragm original for 16ohm early 075?
    From the info Ivica reposted in here, i'd say you can only tell safely by measuring diaphragm thickness with a micrometer gauge.

    OR perhaps by comparing the metal of the diaphragm with later aluminium-only frams. The early type fram used Duraluminium material which looks a bit different in that it produces hues of rainbow colours depending on the angle you look at it. Since the front of your fram seems to have a thin layer of debris, you can probably judge the existence of those hues only when looking at the back of the metal.


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