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Thread: Need help designing a subwoofer

  1. #16
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    Quote Originally Posted by RMC View Post
    RE in this size cabinet.

    RE The single 15", ported in this cabinet seems reasonable, if not ideal.

    My understanding is the OP is still talking about his 1.9 cu. ft. box net.

    I don't see how he would make a valid 2235H cab in such small volume tuned to 28hz. The typical 2235 box used is 5 cu.ft. tuned to 30hz...

    Something seems to be missing
    I measured the box again, and came up with 5.30 cubic feet, not counting anything inside like bracing. That wouldn't be all that much, 2x2 cleats inside and probably a couple of 2x4s across the width.

    Like I said, it seems to me that splitting the volume into 2 ported cabinets would just be way too small for each driver, that was my original idea, and the source of the approx 2 cu ft numbers. I now admit that plan is pretty much DOA.

    But the calculations that I did for 1 driver in about 5.5 cu feet seem to be promising, even if not ideal. How about this idea? If I change driver from a 140 to a 2235 at sometime in the future, is that plan feasible with my idea of being able to easily modify the ports?

    I will admit again that-1, I realize this is not ideal. 2- I really don't know how to do this. So working within the limitations of what I want, I'm trying to determine what is even possible.

    One of the problems I'm having is that the specific drivers aren't listed in any of the design programs that I'm using, and I've seen multiple, conflicting specs for this speaker, and when I manually enter them into WinISD, it doesn't like them anyway.

    I'll post the spec sheet I was using later, and maybe someone can explain to me the reason for what seem to be differing values for the same driver, IDK.

  2. #17
    Senior Member Odd's Avatar
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    Download WinISD verson 0.44 this has the parameter for JBL D140


    Linearteam: WinISD

    43XX (2235-2123-2450-2405-CC 3155)5235-4412-4406-4401-L250-18Ti-L40-S109 Aquarius lV-C38 (030) 305P MkII

  3. #18
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by RMC View Post
    RE in this size cabinet.

    RE The single 15", ported in this cabinet seems reasonable, if not ideal.

    My understanding is the OP is still talking about his 1.9 cu. ft. box net.

    I don't see how he would make a valid 2235H cab in such small volume tuned to 28hz. The typical 2235 box used is 5 cu.ft. tuned to 30hz...

    Something seems to be missing
    I thought it was determined that L220 cabinet has 6 ft.³ of internal volume.


    Widget

  4. #19
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    Quote Originally Posted by Mr. Widget View Post
    I thought it was determined that L220 cabinet has 6 ft.³ of internal volume.
    Widget
    I took the exterior measurements and subtracted 3/4 of an inch for each dimension, assuming 3/4 plywood. That gave me an assumed interior volume of 9165 ci, or 5.3 cu ft. Again, not accounting for any bracing or what-have-you.

    And I played around with that older version of WinISD, I think I like it better. I do see that the 2335H would be almost ideal for this. But that leads me back to my other question. That is, for the two plots I made for each driver in the same box, besides the box volume which doesn't change, what alters the characteristics of the box in regards to the box frequency? Is that altered solely by the port design?


    Attached is the sheet for driver parameters that I was using. Why do the first two pages give the various values in metric on one page, and Imperial on the other, with no obvious key to me about which drivers are noted in what units? It seems obvious to me that the xMax on my driver was not 5.08 inches, but then again, as far as I could tell, it didn't specifically state what units it was referring to.

    Theile_Parameters.pdf

  5. #20
    Administrator Robh3606's Avatar
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    That would be millimeters


    Rob
    "I could be arguing in my spare time"

  6. #21
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by enelson14 View Post
    That is, for the two plots I made for each driver in the same box, besides the box volume which doesn't change, what alters the characteristics of the box in regards to the box frequency? Is that altered solely by the port design?
    Box tuning is a function of the box volume and port size and length.


    Widget

  7. #22
    Senior Member RMC's Avatar
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    enelson,

    RE But the calculations that I did for 1 driver in about 5.5 cu feet seem to be promising, even if not ideal. How about this idea?

    Well its feasible. A 15" takes .2 cu ft in the box and you seem to want minimal bracing so say it will be .3 cu ft, so now you have a 5 cu ft net box ( vent volume remaining to be seen).

    RE If I change driver from a 140 to a 2235 at sometime in the future, is that plan feasible with my idea of being able to easily modify the ports?

    Maybe. Some extendable round ports are sold, you need to see in what diameter, this gives the possibility of varying tuning by extending or shortening the tube. You make it tight fit and apply inside at junction of tube and box some temporary silicone (removeable) for sealing. However i have some questions about the possible losses of extendable tubes.

    RE One of the problems I'm having is that the specific drivers aren't listed in any of the design programs that I'm using, and I've seen multiple, conflicting specs for this speaker, and when I manually enter them into WinISD, it doesn't like them anyway.

    Older Win ISD versions had some bugs, plus if the auto calculate parameters function is activated then ISD may change the numbers you input for calculated values (should be close).

    You need to take the parameters from JBL parameters table and input them in the software with driver model that should do the trick.

    RE what alters the characteristics of the box in regards to the box frequency? Is that altered solely by the port design?

    Widget already answered this.

    Other aspects of port design, choice of port shape: round, square, rectangular, triangular doesn't matter as long as its area is the same for each considered. The easier to modify for you might be the round tube.

    The number of ports used is also relevant in design, e.g. 2 smaller tubes instead of a single larger one (same area).

    Another level of port sophistification you may not need would be flared port (with a "horn" at each end) instead of flanged (straight tube with one end flush to baffle exterior), the latter is simpler for you and does the job in most cases.

    Richard
    POWERED BY: QSC, Ashly, Tascam, Rolls Mosfet, NAD, and Crest Audio

  8. #23
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    Quote Originally Posted by Robh3606 View Post
    That would be millimeters
    Rob
    Right, figured that. But the first two pages give differing units of measure, and all the following pages don't appear to differentiate them. Am I missing something there, or are you just supposed to know?

    Quote Originally Posted by Mr. Widget View Post
    Box volume and port size and length.
    Aha! So then my idea of a removable panel to hold the ports is not too far off base? My thought was to design a set of ports for both sets of drivers, one for the K140, and another that would improve performance if used with the 2235H or some other, more suitable driver. Thoughts?



    Quote Originally Posted by RMC View Post
    Some extendable round ports are sold, you need to see in what diameter, this gives the possibility of varying tuning by extending or shortening the tube. You make it tight fit and apply inside at junction of tube and box some temporary silicone (removeable) for sealing. However i have some questions about the possible losses of extendable tubes.
    What I had in mind was to create a rectangular panel on the front of the cabinet approx 16" wide and 6" tall that could be removed. The panel would be fitted with conventional PVC tubing, tightly fitted in the panel holes, but any changes could be accomplished by making another panel with different tubing configurations.

  9. #24
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by enelson14 View Post
    Aha! So then my idea of a removable panel to hold the ports is not too far off base? My thought was to design a set of ports for both sets of drivers, one for the K140, and another that would improve performance if used with the 2235H or some other, more suitable driver. Thoughts?


    What I had in mind was to create a rectangular panel on the front of the cabinet approx 16" wide and 6" tall that could be removed. The panel would be fitted with conventional PVC tubing, tightly fitted in the panel holes, but any changes could be accomplished by making another panel with different tubing configurations.
    Yes, a set of removable panels that will each accommodate a different port is an excellent choice. You can play with different tunings for the K140 woofers and then try different woofers if you decide to give that a try.

    One note of caution, you will need to use a gasket to make sure the panel makes an airtight seal. Even a small hole the size of a screw hole will affect the tuning.


    Widget

  10. #25
    Senior Member RMC's Avatar
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    Yup, box air losses, too many people see this as trivial but its not. These negatively affect cab/driver predicted LF performance.
    POWERED BY: QSC, Ashly, Tascam, Rolls Mosfet, NAD, and Crest Audio

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