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Thread: Jbl 4642a

  1. #1
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    Question Jbl 4642a

    Hello friends,

    I have 4 JBL 2242H woofers.
    I want to build the JBL 4642A cabinet for the woofers.
    Anyone can help me with a builing plan, and specially for the inside of the cabinet and the vent port.
    I do have the outside dimensions of the cabinet.

    Thanks in advance.

    Frederik.
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  2. #2
    Senior Member 1audiohack's Avatar
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    I can measure one for you Tuesday when I am in the shop if no one gets it sooner.

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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    Thumbs up

    Quote Originally Posted by 1audiohack View Post
    I can measure one for you Tuesday when I am in the shop if no one gets it sooner.

    Barry.
    Hello Barry, that would be great.

    Thanks in Advance !

    Kind regards,

    Frederik.

  4. #4
    Senior Member duaneage's Avatar
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    Quote Originally Posted by FrederikH View Post
    Hello friends,

    I have 4 JBL 2242H woofers.
    I want to build the JBL 4642A cabinet for the woofers.
    Anyone can help me with a builing plan, and specially for the inside of the cabinet and the vent port.
    I do have the outside dimensions of the cabinet.

    Thanks in advance.

    Frederik.
    I would measure the parameters of the drivers and verify what box and port they need to perform at their best. Also it will allow you to check the drivers are related in specs.
    But maybe a box copied from a production run will work ok.
    Why buy used when you can build your own?

  5. #5
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    Quote Originally Posted by duaneage View Post
    I would measure the parameters of the drivers and verify what box and port they need to perform at their best. Also it will allow you to check the drivers are related in specs.
    But maybe a box copied from a production run will work ok.
    Thanks for your comment.
    I want to build existing JBL cabinets with the original JBL specs.
    I am sure the engineers at JBL have enough knowledge to calculate a good cabinet like 4642A.
    That cabinet is designed for 2x 2241H and should therefor suit or even suit better with 2242H.

    Frederik.

  6. #6
    Senior Member 1audiohack's Avatar
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    The port dimensions are:

    15.75” X 7.0” Depth is 15.5”.

    The 4642A port and enclosure is the same as the 5749 which uses 2242’s.

    There are no braces in these boxes other than the rigidity the port gives the baffle.

    All the best.
    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  7. #7
    Senior Member RMC's Avatar
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    RE: "That cabinet is designed for 2x 2241H and should therefor suit or even suit better with 2242H."

    Though one might be wondering (not me) why JBL didn't dare model the 2242 driver in 10 cu.ft. sealed AND vented boxes in the driver's spec sheet, contrary to what they did in both 2240 and 2241 Spec Sheets. For the 2242 Spec Sheet the sealed box used was 10 cu.ft., however the vented box modeling done used a smaller 8 cu.ft. enclosure this time, like they did for the 4645B for example (one woofer). As per the usual rule, twice the box volume for two woofers would mean 16 cu.ft. here.

    Moreover, the "retrofit" paragraph (2241 to 2240 enclosure) in the 2241 spec sheet dated 12/95 was not repeated in the 2242 spec sheet about a possible "retrofit" of 2242 to 2241 enclosure. Food for thought.

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    Quote Originally Posted by RMC View Post
    RE: "That cabinet is designed for 2x 2241H and should therefor suit or even suit better with 2242H."

    Though one might be wondering (not me) why JBL didn't dare model the 2242 driver in 10 cu.ft. sealed AND vented boxes in the driver's spec sheet, contrary to what they did in both 2240 and 2241 Spec Sheets. For the 2242 Spec Sheet the sealed box used was 10 cu.ft., however the vented box modeling done used a smaller 8 cu.ft. enclosure this time, like they did for the 4645B for example (one woofer). As per the usual rule, twice the box volume for two woofers would mean 16 cu.ft. here.

    Moreover, the "retrofit" paragraph (2241 to 2240 enclosure) in the 2241 spec sheet dated 12/95 was not repeated in the 2242 spec sheet about a possible "retrofit" of 2242 to 2241 enclosure. Food for thought.
    Thanks RMC. I will check that.
    Frederik.

  9. #9
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    Quote Originally Posted by 1audiohack View Post
    The port dimensions are:

    15.75” X 7.0” Depth is 15.5”.

    The 4642A port and enclosure is the same as the 5749 which uses 2242’s.

    There are no braces in these boxes other than the rigidity the port gives the baffle.

    All the best.
    Barry.
    Thanks alot Barry !
    Frederik.

  10. #10
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    Quote Originally Posted by RMC View Post
    RE: "That cabinet is designed for 2x 2241H and should therefor suit or even suit better with 2242H."

    Though one might be wondering (not me) why JBL didn't dare model the 2242 driver in 10 cu.ft. sealed AND vented boxes in the driver's spec sheet, contrary to what they did in both 2240 and 2241 Spec Sheets. For the 2242 Spec Sheet the sealed box used was 10 cu.ft., however the vented box modeling done used a smaller 8 cu.ft. enclosure this time, like they did for the 4645B for example (one woofer). As per the usual rule, twice the box volume for two woofers would mean 16 cu.ft. here.

    Moreover, the "retrofit" paragraph (2241 to 2240 enclosure) in the 2241 spec sheet dated 12/95 was not repeated in the 2242 spec sheet about a possible "retrofit" of 2242 to 2241 enclosure. Food for thought.
    Member Barry advised me to look at the 5749 cabinet that is identical with the 4642A cabinet, and the 5749 uses 2x 2242H.
    Frederik.

  11. #11
    Senior Member RMC's Avatar
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    I know, i checked it myself, even though i don't doubt at all Barry's info. JBL has not been particularly consistent in the info surrounding the 2242 vs its ancestors. Also, in spec sheets, which are a form of marketing, there's info given, as well as the unsaid, which the user is left to figure out by himself in "reading between the lines" and comparing the data with other similar models. Sometimes this leads to interesting finds the user has to interpret and decide on their impact, if any, this might have on his project.

  12. #12
    Senior Member RMC's Avatar
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    SOME OBSERVATIONS ABOUT 2242H/5749

    Modeled the 2242 in speaker software to see what i would get for this "Maximum Output" described driver. Ultimate SPL drivers generally have maximized mid band sensitivity at the expense of some LF capability/linearity. The other side of the coin being naturally the 2245H which can pump, by itself, flat & deep bass. But SR and Hi-Fi/Monitoring are two different ball games. Sort of quantity vs quality.

    5742 system Tech Sheet (which uses the 5749 LF cab) indicates F3 30hz, 25hz @ -10 db, stock form (no DSP), not really usable response when 10 db down in my view.

    Used one 2242 in 10 cu.ft. Fb 30hz box (same as 2245 box btw) which JBL didn't show in the former's spec sheet. On pic, the top curve is 10 cf and the bottom curve is 8 cf, both Fb 30hz, like on spec sheet. 8 cf cab showing -6db @ 30hz or so, and not a big LF gain in using the larger 10 cf cab. My bottom curve is similar shape to JBL 2242 tech sheet.

    Simulation with half-space loading, whereas JBL's is hemispherical free-field, the latter a little less favourable to driver? Might have been done this way because this driver would typically be used outside in stacked boxes on a stage for example. 5749 LF box data is given for free field probably representing another typical use outdoors, like hanging.

    The 99 db 2242 sensitivity is taken 100-1000hz hence a higher figure, kind of a little cheat though in view of sub/VLF use. Had they taken sensitivity at say 20 up to 100 hz or so, seemingly a logical bandwidth to measure a sub, results would have been lower according to my modeling.

    The 104 db sensitivity rating for the 5749 cab is based on the higher mid-band sensitivity with two drivers in parallel. But fed with 2.83V @ 4 ohms which is two watts (voltage squared divided by impedance = watts), so not one watt like they did for the 4642A (2241H). Should have been 2.0V @ 4 ohms for one watt. Another little cheat. Marketing is still king re efficiency and related SPL.

    To use the 2242 in the 5749 sub they basically "chopped off" the higher end with a 220hz low-pass filter. Keeping only a narrow bandwidth of the response (30-220hz) for LF application. The type of response curve with such application was shown in a graph of the 4642A spec sheet the OP posted in post # 1.

    Quick look, haven't found a tech sheet specific to 5749. Didn't find a similar graph in 5749 Tech Manual (naturally), but neither in 5742 system tech sheet which uses the 5749 LF cab. Not a big deal since 4642A info shows the idea LF response wise, its not rocket science. However, that graph with higher SPL numbers is not stock or usual form, its top curve is 1 Pi (more boundaries) and the second curve (2Pi) is increased with an EQing 12 db HPF @ 25hz with Q=2. Then their numbers are bound to look more impressive than in my modeling, but i'm no marketing guy.

    However, when most of the mid-band reference level (where sensitivity is measured) is "taken out" by the low-pass xo, then the box has fairly lower average sensitivity in VLF (standard form) compared to mid-band level. Plus in doing so the extra 1 db mid-band sensitivity above 200hz is waived, not a big loss for that one. In actual VLF use JBL's 104 db sensitivity rating appears optimistic, if it wasn't for the two watts and/or the addition of an EQ filter as the case may be.

    DSP and Power being relatively cheap, that seems to be the key here to get high level low bass. Seems the 2242 main advantages are higher power capacity, larger xmax, plus its huge excursion before damage so guys can beat on it with less fear of destruction, though at some point even more driver distortion will occur.

    Richard

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    Last edited by RMC; 02-19-2021 at 04:42 PM. Reason: Minor corrections or additions

  13. #13
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    How about the bass section from the 5742 cinema system? cab? Its designed for dual 2242...25Hz at -10dB, 30Hz at -3dB

    https://jblpro.com/en/products/5742

    Edited to add...oops, I see there was already mention of it...

  14. #14
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    Jbl 5749

    Quote Originally Posted by 1audiohack View Post
    The port dimensions are:

    15.75” X 7.0” Depth is 15.5”.

    The 4642A port and enclosure is the same as the 5749 which uses 2242’s.

    There are no braces in these boxes other than the rigidity the port gives the baffle.

    All the best.
    Barry.
    Hello again Barry,

    I am going to build the cabinets very soon.
    Just one more question for being sure: how did you mesure the port dimensions?
    It could be inside or outside dimensions.
    Is the depth dimesion with the thickness of the front panel included?
    What is the thickness of the vent panels?
    If you could clear it out for me with a drawning i will be one of the happiest JBL lovers persons on the planet.

    Thanks in advance.

    With kind regards.

    Frederik.

  15. #15
    Senior Member 1audiohack's Avatar
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    Hello Frederik;

    All port measurements given are port internal dimensions and include the front baffle thickness in the length measurement.

    There is nothing in these boxes that is not made from 3/4” thick material, port walls included.

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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