About to put box together, one last look and 2 questions, PLEASE look!

Discussion in 'Archived Threads 2001-2004' started by Trenton McNeil, Feb 15, 2001.

  1. Trenton McNeil

    Trenton McNeil Second Unit

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    Okay, about to slap this bad boy together, need to find out
    what the following two values are:
    Ql and Qa
    Not sure what these numbers mean, I figure I should before I
    put the crazy glue to work on the sonotube tomorrow night.
    Here's an image of what I have got so far, tuning to 18.0hz:
    [​IMG]
     
  2. Patrick Sun

    Patrick Sun Moderator
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    Ql is the Q of the leakage in the box.
    Qa is the Q of the absorption in the box (when you stuff it with polyfill).
    Leave the numbers as is if you don't plan on stuffing polyfill in the sub. I only lined mine with batting, no stuffing (yet).
    The Qa numbers get smaller depending on the percentage of the stuffing, and this will "theoretically" move the SPL level in the low end upwards, so your F3 will move up if you start stuffing the enclosure. But in real life, it won't be as bad as it looks due to the rest of the room helping out the low end for a lower Q alignment.
    Just go with what you got (sure you don't want to lower that tune to get a little extra driver protection? - means 2 longer 4" ports around 20" I think.)
    ------------------
    PatCave ; HT Pix ; Gear ; Sunosub I + III ; DVDs ; LDs
     
  3. Trenton McNeil

    Trenton McNeil Second Unit

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    I thought 18Hz was pretty low actually. Anything lower, and
    I wind up screwing up my response curve pretty drastically,
    and moving myself into a larger enclosure. Ports are cut,
    glued into place, everything is done being painted, and its
    all getting put together with poly batting around the inside
    (not going to stuff it).
    I won't be listening to the system near reference level very
    often at all, mostly want to bring out the real low end of
    things during normal moderate listening levels, and be able
    to do the occasional BOOM when the occasion warrants. [​IMG]
    My next sub, however, will be a DIY for the car. Going to
    have to be a ported small box, probly with 2 JL 10" subs in
    it, that one should be interesting, if not as daunting a
    task. This one will be called upon to BOOM quite frequently
    during my 15 mile jaunt to work through the traffic. [​IMG]
     
  4. Chris Hoppe

    Chris Hoppe Stunt Coordinator

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    Where did that 15 come from for Ql? Did the proggie put that in by default?
    Typically, that value should be 7 for most boxes.
    Also, I'm not sure what Qa should be, but I don't think it should be anywhere near 100...
     
  5. Trenton McNeil

    Trenton McNeil Second Unit

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    I really have no idea where those numbers came from....
    That's why I'm asking...I don't even know what Q is by
    itself, Patrick...
    HEEEELP!!!!!
    ------------------
    [​IMG]
    I wish I had a dollar for every time I spent a dollar, because then, yahoo!,
    I'd have all my money back. -- Deep Thoughts, by Jack Handey
     
  6. Gregg Loewen

    Gregg Loewen Video Standards Instructor, THX Ltd.
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    I thought Q was the all know god like being off of ST TNG.
    (sorry couldnt resist).
    Gregg
     
  7. Patrick Sun

    Patrick Sun Moderator
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    Q sort of defines what kind of enclosure system you have. A sealed box with result in a Q near 0.5 to 0.58. A well designed, near optimal, vented box/bass reflex box will result in a Q near .707. There's a bunch of little calculations that will lead you to the Q number but I don't know them off the top of my head.
    ------------------
    PatCave ; HT Pix ; Gear ; Sunosub I + III ; DVDs ; LDs
     
  8. Trenton McNeil

    Trenton McNeil Second Unit

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    I modified the Q values to .7 and 50, and things still look
    cool, so at this point, I'm gonna slap it together, and ask
    questions later. I'm sick of working on it. [​IMG]
    Hope to give a full report by the end of the weekend.
    ------------------
    [​IMG]
    I wish I had a dollar for every time I spent a dollar, because then, yahoo!,
    I'd have all my money back. -- Deep Thoughts, by Jack Handey
     
  9. Greg Monfort

    Greg Monfort Supporting Actor

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    Chris:
    >Where did that 15 come from for Ql? Did the proggie put that in by default?
    ====
    Yep.
    ====
    >Typically, that value should be 7 for most boxes.
    ====
    Depends on how well you build them, and how lossy the driver is. Still, 15 IS a bit optimistic. According to Altec, my vented LF drivers have a Ql = 2, just for an extreme example.
    ====
    >Also, I'm not sure what Qa should be, but I don't think it should be anywhere near 100...
    ====
    In this version of Lspcad, 100 = no lining or stuffing. Subtract the lining's volume to figure the lower percentage.
    ====
    Trenton:
    >I don't even know what Q is by itself......
    ====
    Q stands for 'quality factor' and is the ratio of energy stored to energy dissipated/cycle, and there's a bunch of different ones (I can only remember fifteen, but there's more), though many are unrelated to each other.
    So beware, lest you get your Q's crossed. [​IMG]
    ====
    Pat:
    >Q sort of defines what kind of enclosure system you have. A sealed box with result in a Q near 0.5 to 0.58.
    ====
    WRT enclosures, its Q defines the roll-off slope between F3/Fb. Note that these curves only apply to sealed alignments. Qtc (driver + box Q) can be any value from the driver's Qts up to whatever the least possible cab volume equates to. A Qtc = 0.5 is 'critically damped'. Any value lower is overdamped, any higher value is underdamped.
    ====
    > A well designed, near optimal, vented box/bass reflex box will result in a Q near .707.
    ====
    Hmm, a maximally flat vented alignment (optimal) has a Qb = 0.707.
    Your earlier definitions of Ql, Qa, are close. Ql is the box losses at Fb, and Qa is the absortion losses at Fb, but only alter the primary Qtc, Qb, by lowering it. For vented, there's also Qp, vent frictional losses, which is factored in when you check the sim port non-linearity field.
    GM
    ------------------
    Loud is beautiful, if it's clean
     
  10. Patrick Sun

    Patrick Sun Moderator
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  11. Brian Bunge

    Brian Bunge Producer

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    Greg,
    Can you tell me how one could actually measure the Q of a sealed enclosure with a specific driver? Is there a relatively simple way to extract this info. with a test disk, a multi-meter and some handy formulas?
    As always, thanks for the help! You don't happen to design and build speakers for a living do you? If the answer is no, then why the hell not? [​IMG]
    Brian
    ------------------
     
  12. Greg Monfort

    Greg Monfort Supporting Actor

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    Brian:
    I thought I answered this here: http://www.hometheaterforum.com/uub/...ML/002719.html
    I've built what seems like a jillion prototypes to see what did what since I have so little formal education, and most of the math is an indecipherable language to me. I've also built dozens of systems over the decades for friends, co-workers, neighbors, etc., and for awhile built custom in-wall cabs for a local hi-end HT contractor, though he insisted on doing the designs. I had planned to build/sell a few systems using the new Unity horn and Lambda HE drivers, but between delays in production and my health issues, I'm not doing much of anything beyond exposing ya'll to what little I know.
    GM
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    Loud is beautiful, if it's clean
     
  13. Jack Gilvey

    Jack Gilvey Producer

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  14. Greg Monfort

    Greg Monfort Supporting Actor

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    You're welcome. [​IMG] Trust me though, I know enough to know how little I know, if you know what I mean. [​IMG]
    I don't have the LDC, but I never recommend it because IMO it has too many errors, or at least gives folks the wrong ideas, based on numerous discussions where something gets quoted from it.
    GM
    ------------------
    Loud is beautiful, if it's clean
     
  15. Jack Gilvey

    Jack Gilvey Producer

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  16. Brian Bunge

    Brian Bunge Producer

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  17. Greg Monfort

    Greg Monfort Supporting Actor

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    Glad I can help, and thanks for the well wishes. Unfortunately, short of getting numerous nerve grafts in my spinal column, there's not much hope of getting better. [​IMG] At least it's not life threatening AFAIK. [​IMG]
    Sadly, no, I'm not kidding. [​IMG] I rely on books, AES papers, others posts (such as Dan Wiggins), etc., for the basic formulas, then get various folks I've known over years who do know the language to manipulate/reduce them for me to get what I want. Some have tried explaining why they did what they did, but alas, it was usually wasted on me. My dad and brother were math whizzes, but I took after my mother, so I keep copious notes with examples, for reference. Plus I have most of them loaded into spreadsheets to get quick answers.
    GM
    ------------------
    Loud is beautiful, if it's clean
     
  18. Trenton McNeil

    Trenton McNeil Second Unit

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    Well I finished putting it together, and didn't change anything. I don't know if its good or not, but the opening sequence of Toy Story 2 almost dropped 3 pictures, a clock and a candelabra to the floor, and those things were across the room from the sonotube.
    I am addicted to Bass now, already gearing up for a car box. Stop the insanity!
    Greg, I must thank you for your opinion and knowledge as well, it has all come very handy in designing this box, and doesn't go unappreciated! I, too wish you well, and perhaps someday we can get an Atlanta meet together and see who has the biggest, boomiest, cleanest sounding bass in all of the Metro area! [​IMG] a hint...its probably not me!!
    ------------------
    [​IMG]
    I wish I had a dollar for every time I spent a dollar, because then, yahoo!,
    I'd have all my money back. -- Deep Thoughts, by Jack Handey
     
  19. Greg Monfort

    Greg Monfort Supporting Actor

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    >Well I finished putting it together, and didn't change anything. I don't know if its good or not, but the opening sequence of Toy Story 2 almost dropped 3 pictures, a clock and a candelabra to the floor, and those things were across the room from the sonotube.
    ====
    Almost?! Close only counts in horseshoes and hand grenades! You're going to have to step it up some if you want to run with the big boys. [​IMG]
    ====
    >I am addicted to Bass now, already gearing up for a car box. Stop the insanity!
    ====
    He,he, now that the hook's sunk.... [​IMG]
    ====
    >Greg, I must thank you for your opinion and knowledge as well, it has all come very handy in designing this box, and doesn't go unappreciated!
    ====
    My pleasure! Glad you took the plunge. Addicts love company. [​IMG]
    ====
    >I, too wish you well, and perhaps someday we can get an Atlanta meet together and see who has the biggest, boomiest, cleanest sounding bass in all of the Metro area! a hint...its probably not me!!
    ====
    Thanks, and maybe someday...... my system is in pieces right now while some remodeling/repair is being done when $$/health permits. With my 50yr old stick built house, 120+dB organ notes rip drywall joints, and pop drywall nails/screws out in every room. Kitchen cabinets have pulled loose, and the old window glazing is cracking out. [​IMG]
    GM
    ------------------
    Loud is beautiful, if it's clean
     

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