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Thread: Positioning of ports and driver?

  1. #76
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    Quote Originally Posted by Greg_M View Post
    Does this include one diameter minimum from the top or bottom?
    Greetings -

    Large ports will provide more articulate low frequency at the point of resonance. In other words, a tight bass. Large meaning, 5-8 inches in diameter depending on the volume of the cabinet. On a pair of reproduction ALTEC Lansing Capistrano I built, I used two 6" diameter ducts exiting the bottom panel. The down side; the larger diameter port, the longer it must be. The objective it to keep the vent velocity (mach number ) down. At the point of resonance, it doesn't matter where the port is as long as it is not obstructed. A tube port can even be outside of the enclosure, as it does not have to be inside. When calculating port parameters, consider the tube port as a separate physical element in the circuit. For example; if a circuit board layout has been finalized, but later determined that a choke must be added, then make the circuit board larger to accommodate it. The cabinet volume must be increase to accommodate a tube port.

    H.F.

  2. #77
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    Quote Originally Posted by Greg_M View Post
    I think it's extremely interesting that volume can be gained with insulation.
    If there is a formula or way to estimate this, I'd love to include it in my little spreadsheet.
    Thanks again
    Greetings, again -

    The typical volume gained by adding damping material would be 1.4 times the gross volume of the enclosure. Personally, I use damping material sparingly, as too much will suck the live out of the cone. The impression that a highly dampened enclosure adds bass is a misconception. Damping material does two things; attenuate high frequencies, and decrease the velocity of sound at low frequencies. Essentially, damping material fools the speaker into behaving as though it is in a larger enclosure. Adding bass? More like allowing the speaker to produce the low frequencies it already does, unfettered by a small enclosure.

    H.F.

  3. #78
    Senior Member RMC's Avatar
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    Hi Horn Fanatic,

    RE "The typical volume gained by adding damping material would be 1.4 times the gross volume of the enclosure."

    Just to avoid having too high expectations. Its not evident that one can add that much virtual box volume with damping material. It sure was the belief among experts and audiophiles for some time, however:

    "Previously it was thought that the maximum possible increase in effective volume was in the range of 1.4, or 40%, but Leach (1989) provided a more accurate analysis indicating that the maximum ratio is 1.31. In normal practice most loudspeaker engineers observe an increase of perhaps 1.2." (Or 20%) John Eargle, Loudspeaker Handbook, P. 63, Regards,

    Richard

  4. #79
    Member Greg_M's Avatar
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    What an expensive book.
    I thought of buying it for reference, but they want a ton of money for it.

  5. #80
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    Meanwhile.....
    While I'm building on the cabinets, I have one of the speakers being "conditioned".
    Right to left.....
    Astron 12v power supply
    Tenma Audio Generator.
    Boss car amp (usually for sub woofers etc)
    It's been exercising the speaker for almost 24hrs now at 20hz.
    I think I'll run it at the next higher step (28hz) for a while.
    I pushed it at 20hz until it started "clacking" and then backed off enough to make it stop.
    The JBL metal tag fell off the back of the spkr. Easy enough to reglue.

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  6. #81
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    Unfortunately good engineering books are generally expensive. These don't have a large audience nor printing run, making cost per unit much higher. That kind of manual won't appear on best-sellers lists. If you can find a good used copy at reasonable price it may well be worth it.

    JBL's John Eargle wrote a number of respected audio books: Microphone Handbook, Handbook of Recording Engineering, Electroacoustical Reference Data, Loudspeaker Handbook, Handbook of Sound System Design, etc., but the last two cover a good part of it. Those are often used as University level references for Audio Engineering courses. Which explains why sometimes it gets heavy math wise but most of it is ok.

    The Sound System Design book was updated in 2002 by John Eargle and Chris Foreman with a new title: JBL Audio Engineering for Sound Reinforcement. The Loudspeaker Handbook was also updated in 2003. A fellow having both editions of it reviewed the new one and said it was mostly the same text as first edition except with more recent driver model examples and technologies.

    You can get for free SOME of the Sound System Design book's stuff in JBL's own "Sound System Design Reference Manual", 1999 also from Eargle. Just Google JBL's manual and get a pdf file of it from their site.

    Its unlikely there will be any further updates to these books since he passed away some years ago (RIP).

  7. #82
    Member Greg_M's Avatar
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    I tried a few used places and of course ebay and all those that I could find are even more expensive than the new ones off Amazon?
    I did see that the library in Las Cruces has a copy so maybe I can get the Datil library to bring it in for me.

  8. #83
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    Another interesting one, and much cheaper, is Vance Dickason, The Loudspeaker Design Cookbook.

    I have 5th edition but its at the 7th edition now I think. More home theater audio stuff was added which I'm not into. Price on my edition was $35. so quite affordable, a good used one could be a bargain.

    Robert Bullock, Bullock on Boxes, 1991 also interesting

    David B. Weems, Designing, Building and Testing your own speker system, 4th edition, 1997, says $20. on mime (best one for beginner)

    All the above depend on knowledge level you're at or want to be or can stand. What are you looking for?

  9. #84
    Member Greg_M's Avatar
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    I'd like a book that I can learn in to, but is something I can understand now.
    Usually I have to open the book and read a page.

  10. #85
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    My first 2225H is done being conditioned and I did a DATS test on it again.
    This is after 24hrs at 20hz and 24hrs at 32hz

    This is what the software had to say...

    * This data was exported from the Dayton Audio Test System: DATS
    *
    * Piston Diameter = 342.9 mm
    * f(s)= 19.65 Hz
    * R(e)= 6.838 Ohms
    * Z(max)= 179.2 Ohms
    * Q(ms)= 7.299
    * Q(es)= 0.2896
    * Q(ts)= 0.2785
    * V(as)= 272.8 liters (9.635 cubic feet)
    * L(e)= 1.715 mH
    * n(0)= 0.6815 %
    * SPL= 90.44 1W/1m
    * M(ms)= 288 grams
    * C(ms)= 0.228 mm/N
    * BL= 28.98
    * K(r)= 0.04122
    * X(r)= 0.5916
    * K(i)= 0.02001
    * X(i)= 0.7072

    PS
    I did put my Fluke meter on it and got about 6.2 ohms.

  11. #86
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    Your first 2235 done not 2225 as Grumpy indicated...

    I updated a little the info on Weems' book, year and price.

    Since its cheap, then I would suggest you start with Weems book to get a good understanding of the concepts and how they work, its pretty well made and I still refer to it sometimes for specific things. These type of books are not all made the same way with same info. Somethings you'll find in one and other things in another. They're not at the same level either.

    So start with Weems', then move on to Dickason's Cookbook, and when you have pockets full of money you get Eargle's Loudspeaker and Sound System Design handbooks.

    Back later about your latest parameters...

  12. #87
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    Compared to last measurements, this time box relevant parameters (Fs, Qts, Vas) have improved notably, though Vas still somewhat short, but its been shown that Vas is less critical (error has less impact) than some others. Qms is still too high to have Qts on par. RE went up but you measured 6.2

    You lost some efficiency/sensitivity in this second set. Cone mass is even further than it was before (also from spec) as well as Bl increasing again. So there remains a number of mysterious things here.

    I don't have a ready made explanation for all the deteriorations. For example one may risk for efficiency that ever higher cone mass has reduced it, however motor strenght (BL) is shown to have increased also...

    No (efficiency) calculation does consider Fs, Vas and Qes so it'll be interesting to see what the following says:

    Try Dats up to first para. list without doing the Vas measurement, then input the DATS para. you have at that point in Win ISD Driver Editor (para. tab) and let "Auto calculate unknowns" do the calculations for the missing ones and see how they compare with todays para. list as measured by Dats.

    I would input the numbers slowly and look as you go to the ISD calculated numbers, and also to changes made by the auto calculator. It may give you some clues.

  13. #88
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    Could be I am doing something wrong operating the software also.
    It would be interesting to have an original 2235 to measure as reference.

    On the enclosure front, I am at 10,702 cu in (6.2 cu ft).
    If you count the magical 20% from insulation it is 12,842.5 cu in (7.432 cu ft.) however I am not using the latter in WinISD.
    Maybe I should?

    Looks like one 4" vent 4"± long at this point.

  14. #89
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    I'm assuming DATS wise that you are following the instructions and procedures from Dayton Audio.

    RE having an original 2235 to measure as reference, well I've posted (post #41) the parameters of the original 2235H. This should be used as reference or for comparison purposes. There can be small differences from unit to unit but it should generally look like that (not big differences).

    On the enclosure front, I personnaly see no interest in going with a too large enclosure (6.2-7.4 cu.ft), except in a specific purpose which I won't get into here. I don't necessarily agree with, nor endorse, some of the things mentioned in this thread.

    I've already indicated the typical 2235H enclosure is 5 cu.ft. tuned to 30 hz. The other one I know is JBL's B380 which is a little smaller at 4.5 cu.ft. and uses the 2235H. Usage of larger volumes than these aren't from me, so I'll let their proponent(s) deal with the specifics about those and the issues involved.

    There's nothing wrong with going a different route than an already proven design. However one has to know why making that choice, what are the consequences, and how to mitigate the issues. Important to know.

    A 5" vs 4" vent is about the same work and little more cost, so why not go for the 5" and have peace of mind, instead of using a just sufficient 4" one. I'm aware JBL's B380 has a 4 1/8" vent. B380 is 1983. Since then vent size recommendations have increased, and increased again with the newer very high power drivers (e.g. 2KW music).

    In four more recent JBL Speaker building documents I checked (not counting 1983 Audio article), two recommend a 5 cu.ft. box for 2235H, Fb 30 hz (other two don't mention driver). As for vent size for 5 cu.ft./Fb 30 hz box, two mention a 5" tube, one a 6" tube and one 2 X 4" tubes. None for a single 4" dia. vent.

    One day or another guys always end up putting more power in their boxes than initially thought, at the very least to test the beast... You may regret a smaller vent down the road for you or if you ever sell the cabs.

    The "magic" of Fiberglass insulation isn't that magic btw. You need a lot, and my mention of it was in a box salvage mode context, which doesn't really apply to you, having larger than optimal volume already. So if you need to do something it may well be to reduce it, not enlarge it. Read item # 20 on pic, its from JBL.

    Driver limitations in a box have to be recognized and dealt with accordingly. The sky isn't the limit.

  15. #90
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    Sorry forgot the pic...

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