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Thread: Positioning of ports and driver?

  1. #46
    Member Greg_M's Avatar
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    C8R2235 JBL Recone kit $214

  2. #47
    Member Greg_M's Avatar
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    Quote Originally Posted by RMC View Post
    Greg,
    Some show quite sizeable differences between your actual numbers and those from JBL.
    Richard
    Probably because it's a 2225H not a 2235H.
    I just discovered that my memory was playing tricks on me.


    It's different but in a good direction.

  3. #48
    Senior Member RMC's Avatar
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    Greg,

    At least you have genuine JBL cone kits which should be better than cheap aftermarket ones, yes different but in a good direction as you say.

    I think the key for you will be giving these drivers a good break in period, then measure parameters again with DATS 3. At that point the numbers you will get are the deck of cards you'll have to play with in Win ISD. It shouldn't be bad.

    Qts should drop and Vas increase somewhat with the workout. What seems a little more puzzling though is the cone mass measured at 213 gr vs an original 2235H cone having 155 gr. Even more so when Eargle mentions "Normal production variations in cone mass should be negligible, ..." (Loudspeaker Handbook, P.290). Here its a notable 37% more. Maybe test method or procedures involved may explain this? Check.

    Since I'm planning on getting in the near future a DATS 3 what's your take on it up to now, easy user friendly to use or a maze with some pain in the...?

    Richard

  4. #49
    Member Greg_M's Avatar
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    I used the DATS V3 to drive the woofer overnight at about 30hz. So it ran from 14:30 yesterday until about 09:00 this morning. Ran the test again and nothing had changed.

    Did you know about the little ring weight that goes in the 2235 cone (maybe under the dust cover)? It's to add mass (obviously) so it can reach that low Fs. That might be where the added weight comes from?
    Since the recone guy used the 2235 recone kit, it might be in there helping to push the Fs of the 2225 down from 40hz to it's current state.
    Just guessing about all this.

    Soon as I get one of the boxes done being braced, I'll mount up one of the 2225s and let it run for a while at 30hz or so under some power and see if anything changes.

    As far as DATS V3, it's pretty easy to use. You'll need something like Blu-Tack to stick some weight to the cone for the second part of the test. When I did the 10" Klipsch woofer the 75 grams of the Blu-Tack was enough by itself. When I did the 2225 I had to use the Blu-Tack and a tape rule to get enough weight to make DATS happy. There a few YouTube videos that cover it.

    Using the measurements from the DATS gizmo, I fed WinISD all the new data. and finally got a call out for the ports (for the 6.7144 cu ft box) of 2ea 3" tubes 4.15" long. Put in the figures in to "Port Length Calculator" and got 2ea 3" tubes 4.18" long, then "Box Port Design" and got 2ea 3" tubes 4.54" long.

    I'll wait until I run these speakers in some more before I actually cut holes in the back of the boxes. Meanwhile I can just use the box to hold the woofer vertically and run it for a while.

    I think I'm making progress.

  5. #50
    Senior Member grumpy's Avatar
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    For anyone trying to follow this thread: if a 2225 has its soft parts replaced with a JBL factory 2235H recone kit, it is no longer a 2225, but a proper 2235, unless the mass ring is left out, in which case it is a 2234.

  6. #51
    Senior Member RMC's Avatar
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    Greg,

    Yes I knew about the mass ring, this thing is mentioned on the forum regularly since many folks have or want 2235. Barry here has shown twice recently with his measurements that the gain in lower Fs with the mass ring on is about 3-4 hz if I recall right. Not a huge gain bass wise.

    RE "Ran the test again and nothing had changed." Not even a bit yet is surprising. Good idea to continue the break in, preferably as long as it takes to see numbers change at least a little and then some. The drivers waited 7 years so they can wait a few days more, in workout, before getting installed for sound.

    I'm not overly concerned about Fs at this point. But more about Qts and Vas for your box shell size (6.7 cu.ft. is that your calculated net or gross internal volume? Bracing, driver, etc. accounted for?). If the driver suspension system (surround and spyder) can start getting more compliant ("loosening") then those two parameters should start to move.

    Keep in mind what Grumpy wrote to avoid confusion. Sure you're making progress, designing boxes is science based and you have to go through many steps, including the nitty-gritty stuff. You may feel entangled in details now but its certainly an investment in knowledge/learning for this and the next pair...

    Thanks for the feedback on your DATS 3 experience up to now.

    RE port size and length, don't be surprised if you get some small differences between one software and another. The Editors of Win ISD themselves wrote a 20 page tech paper on this using 11 different softwares to explain why results vary from one to another. Shortly, it depends on the assumptions made (e.g. temperature, speed of sound, etc.) and equations used.

    For your boxes 2 X 3" vents is bare minimum specially if you'll feed those with a fair amount of watts. I'd be leaning more towards 2 X 4" or even 1 X 5" if practical (remember the 1rst port resonance thing?). Regards,

    Richard

  7. #52
    Member Greg_M's Avatar
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    The cu ft box measurement is gross, not subtracting 1x1" corner bracing or the speaker itself. The box is 30" tall, 17" wide 22.75" deep inside.
    I'll be pushing the speakers with a McIntosh MC275 so only 75 watts per channel.

    I probably should mention that I live on the Continental Divide at 7,350'. The air is quite thin and very low in humidity. Maybe this is altering some of the figures?
    I moved here to do astrophotography. Still building the observatory (yet another project) but it's too cold to work outside so I'm doing inside projects now.

    Also, I am no professional using the DATS system so I could be screwing something up in its use. If anyone has a check list or suggestions I sure wouldn't take offense at a little critiquing in its use.

    If anyone would look at my WinISD figures, I'd be glad to make my project file available.

    If all this is for naught I can still use the KLF-20s.

  8. #53
    Member Greg_M's Avatar
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    Quote Originally Posted by grumpy View Post
    For anyone trying to follow this thread: if a 2225 has its soft parts replaced with a JBL factory 2235H recone kit, it is no longer a 2225, but a proper 2235, unless the mass ring is left out, in which case it is a 2234.
    I'm remembering now a conversation with the speaker reconing guy (because I couldn't find any 2235s that were not crazy expensive) where he told me about reconing the 2225s with 2235 kits saying what you are saying. He said the frames are the same it's just the soft parts that differ.

    The 2225s are quite a bit more plentiful as they were/are used a lot in theaters.

    I had forgotten all this until you mentioned it.
    Thanks
    G

  9. #54
    Senior Member RMC's Avatar
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    Greg,

    Looking at your Win ISD figures now is a little premature pending you get more final numbers after the drivers' good workout. Also too early to say if all this is for naught. Lets stay positive and keep hope, before switching to salvage mode.

    Those 1X1" are joints reinforcement mainly. Not really cabinet panel bracing which you will need with such box size. You may still use these.

    Your 6.7 cu. ft. gross box is basically a 5 cu.ft. net box with almost 25% overvolume for losses, bracing, drivers, vent, etc. Seems acceptable.

    The minimum panel bracing I would use, in view of the low 75 W /channel, is 2X2" lenghts for a front to back panel brace midway and same for a side to side panel brace midway or so to reduce panel vibrations, while taking little space inside the box. So a cross type bracing job, simple to do and it won't take away much box volume. You need to keep bracing in mind specially on your front panel layout before making more holes.

    The air volume displaced by a 15" driver is given at 0.2 cu.ft. (6L) by JBL, useful to know for gross/net box calculations.

    The altitude you live at may have some effect but never lived that high so not really familiar with the impact & details. e.g. I know in my snowblower manuals there's references to using it at higher altitude, I think 4,ooo ft.+ (carb air/fuel mix special adjustment?), but never looked closely at altitude aspect since I live at low altitude. Probably more for Colorado folks who also get a fair amount of snow.

    Then atmospheric pressure must be different too? Doesn't seem to impair mustache growing though, that should make you smile. Nice.

    NM and Colorado members here living on higher grounds may be in a better position than me to help you with the altitude aspect. Regards,

    Richard

  10. #55
    Member Greg_M's Avatar
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    After doing some subtracting I came up with 6.3529 cu ft. net

  11. #56
    Senior Member RMC's Avatar
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    what have you subtracted? 6.36 cu.ft. net seems pretty high to me when all in

  12. #57
    Senior Member Ian Mackenzie's Avatar
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    Hi Greg,

    Richard has you on track for a nice bass reflex system.

    For years l used to do lots of calculations to work out the net volume. I felt like l knew every inch of the design but still the result was not always quite right.

    That said once you try it out it’s fairly obvious if the tuning is off. The bass will obviously sound restrained or boomy.

  13. #58
    Member Greg_M's Avatar
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    Quote Originally Posted by RMC View Post
    what have you subtracted? 6.36 cu.ft. net seems pretty high to me when all in
    0.2 cu ft for the spkr and 279 cu in for the corner bracing.

  14. #59
    Senior Member RMC's Avatar
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    Greg,

    The typical 2235 box is 5 cu.ft. net tuned to 30 hz. Doesn't mean others are forbidden but then you need to model such to see the expected result with different tunings and volumes. Yes in salvage mode volume can be modified somewhat.

    Richard

    Mod to volume: to reduce, putting pieces of wood or books even bricks (latter too heavy) to take excess space in cab. To increase, much thicker glass wool or similar to create virtual volume.

  15. #60
    Senior Member RMC's Avatar
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    And you haven't counted good bracing yet...nor vent and the other drivers in the cab

    Horns & drivers space taken .05 to 0.1 cubic foot (JBL)

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