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Thread: 2012H enclosure size?

  1. #1
    Senior Member Baron030's Avatar
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    2012H enclosure size?

    Does anyone know the ideal enclosure volume and port dimensions for the JBL 2012H Midrange/Mid-Bass Transducer?

    JBL's product sheet recommends 10-30 liters and an example of 8.5 liters tuned to 75 Hz.

    What would the size of a 75 Hz port be?



    I happen to be building a version of Daniel's Ancient Audiophile's quest for the Ultimate Home System.



    So, any advice would be welcome.

  2. #2
    Senior Member Baron030's Avatar
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    2012 Headaches

    Well, it has been several months now, and 60 people have chosen to view this thread.

    But, unfortunately, no one has offered me any advice on the 2012 transducer. Since, I have about $500 tied up in a pair of these drivers. I have been forced to search else where for some sort of a workable solution.



    Whenever, I have tried using an internet speaker enclosure calculator program, the resulting enclosure dimensions appeared to be way out of line with JBL’s recommendations. In both Bass reflex and Acoustic Suspension enclosure designs the internal volume appeared to be way too small. This has only added to my confusion about what to do with these drivers.



    Unfortunately, it would appear that this web site does not offer a lot advice on the 2012. But, I did come across a very helpful piece of advice when I widen my search to include “Dog Boxes”. Long time member “Giskard”, was helping someone with an enclosure question about the 2202H drive, when he stated the following:



    Yes, but you might prefer the overall sound of ported instead of sealed. It's a preference and you should give both a listen to see which you prefer. The Qts of the 2202H is intentionally low so that any reasonable size enclosure (1.5 to 2.0 cubic feet) you put it in that is sealed will result in maximum transient response. That's what the JBL midrange transducers are designed for - maximum transient response in sealed enclosures. You might want to look on the Internet and read about Acoustic Suspension versus Infinite Baffle. The 2202H in a 1.5 to 2.0 cubic foot sealed volume behaves like an Infinite Baffle design whereas a transducer such as the LE10H in the same size volume behaves like an Acoustic Suspension design. Most JBL midrange transducers are intentionally designed to operate in sealed enclosures as Infinite Baffle systems to maximize transient response.



    You can also play around with BB6P and see how different sized sealed volumes affect power handling, efficiency, response, group delay, etc. A Qtc of ~ 0.5 is critically damped, anything below that enters the realm of an Infinite Baffle design (the transducer begins to act as if it were in "free air" and the enclosure volume begins to have diminishing effect on the transducer). A Qtc of 0.577 is a Bessel response and a Qtc of 0.707 is a Butterworth response. It's probably best to stay away from anything higher than 0.707 in general.



    Quote:

    Originally posted by maxwedge

    Is there a minimum depth that I need to be aware of that could cause problems?



    Sure, your internal physical dimensions for any midrange enclosure should follow the "golden ratio" as midrange is the most critical and you want to avoid reinforcing internal standing waves like the black plague. There have been several discussions on this forum about the topic and numerous solutions worthy of investigation. Sonotubes, non-parallel sides, non-parallel baffle and back, etc.



    I've really come to love those beasts.



    Well, thanks to Giskard, I finally have an understanding of just how unusual the 2012 driver is. And that the ideal enclosure for this driver can be either an Infinite Baffle of 10 to 30 liters or a Bass Reflex enclosure of 8.5 liters tuned to 75 Hz. Since, mid-bass drivers are generally operated one to two octaves higher than their resonance, any differences in the frequency response between the enclosures shouldn’t be noticeable.



    Currently, I have a pair of these drivers temporarily housed in Infinite Baffle enclosures with a net internal volume of 11 liters. But, I do plan on converting one of my test enclosures to a Bass Reflex design for a direct comparison.



    Also, I may have found a simple solution for the 2012’s rising frequency response. If a 1.5mH coil is wired is series with the driver, the added reactance appears to flatten the response over the 400 to 1000 Hz range. Unfortunately, this simple solution will only work if you are using an active crossover and a separate amplifier for the 2012 drivers.

    Hopefully, I will be testing 1.5mH coil equallizer and base reflex design soon.
    And will let you know what the results are.

    Baron 030

  3. #3
    johnaec
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    'Sorry I missed this. An 8.5 liter box tuned to 75 hz requires a 3" dia port 9.1" long. Since port velocity will probably not be a factor, you could also use a port of 5 sq.in. and 6" length for the same response.

    John

  4. #4
    Senior Member stevem's Avatar
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    Me Too

    Baron, at what frequency are you trying to cross over? I also am trying to optimize these drivers, and in fact I'm in the process of building a pair of ported enclosures for them right now. I have found that in a sealed enclosure of about 30 liters, the response is down about 4 or 5 db at my crossover frequency of 300 Hz. Although I am also concerned about transient resonse, I'm hoping that reflex loading these drivers will flatten them at least at the crossover frequency. I have chosen to use a program suggested Vb of 8.8 liters tuned to 93 Hz. The higher tuning frequency should yield a flatter resopnse at 300 hz verses more extension at low frequencies. I should have them up and running by the end of this weekend. I'll let you know what I think then.

  5. #5
    Senior Member Baron030's Avatar
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    Hi John



    Here is what I am going to be trying soon.

    An enclosure with a net internal volume of 8.5 liters (0.3 cu’), works out to be about 9.5” x 12 7/8” x 6.25” is size. This is taking into account for the driver, 2 ports, and ¾” x ¾” cleats running along each inside edge. For the 2 ports, I am going to use 1 ½” Schedule 40 PCV pipe. The pipe has an inside diameter of 1.578125” and if my calculations are correct the correct length should be 4.9782” for 75 Hz. Oh, and as part of my calculation, I am assuming a 1 ¼” thick front panel. Hopefully, this should keep the port opening from coming too close to the rear panel. And believe me, It really is all a tight fit is such a small box.



    I know this is going to sound strange. But the JBL Venue system uses a metal enclosure for this driver. It is to reduce power compression by dissipating heat out of the enclosure.

    So, if I decide to go ahead with a bass reflex design, I am planning on using 2 ports.

    One port will be mounted near the top and the other near the bottom of the enclosure. This will allow for a cooling convection current to flow through the enclosure.

    And since, I will be using a Crown K1 to drive these 2012s with 350 watts per channel, heating may be come an issue.

  6. #6
    GordonW
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    Yeah, with the slightly rising response this driver exhibits (not to the degree of the 2123, but in the same realm), a higher-Q sealed enclosure (ie smaller) could definitely be used to "prop up" the bottom end response of the driver, to make it easier to crossover. It's quite easy to expect 300 Hz to be slightly raised, with an enclosure with a Q of 1 or so, compared to one with the traditional sealed enclosure Q=.707. It'll model showing a peak in the box-modelling programs, but IRL, once you add the effect of the rising natural driver response, it'll be much closer to flat...

    As for vented- unless you're going to use it in such a way as to need serious bottom-end excursion out of the driver (ie, a 100 Hz crossover point, or something similarly low), I'd shy away from vented enclosures. It's always harder to passively cross-over a vented enclosure as a high-pass, than it is a sealed enclosure. That second impedence peak above box resonance is a PITA to deal with, using a passive highpass crossover in a ported midrange system...

    Regards,
    Gordon.

  7. #7
    Senior Member stevem's Avatar
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    Quote Originally Posted by GordonW
    As for vented- unless you're going to use it in such a way as to need serious bottom-end excursion out of the driver (ie, a 100 Hz crossover point, or something similarly low), I'd shy away from vented enclosures. It's always harder to passively cross-over a vented enclosure as a high-pass, than it is a sealed enclosure. That second impedence peak above box resonance is a PITA to deal with, using a passive highpass crossover in a ported midrange system...

    Regards,
    Gordon.
    I'm using active crossovers. Do you think a vented enclosure would be a problem in that case? Maybe my sealed box is just too large (it's about 1 cubic foot).

  8. #8
    GordonW
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    Quote Originally Posted by stevem
    I'm using active crossovers. Do you think a vented enclosure would be a problem in that case? Maybe my sealed box is just too large (it's about 1 cubic foot).
    As long as the crossover point is AT LEAST 1.5 octaves AWAY from the port tuning frequency, it should work OK. Any closer, and the phase shift from the vented system rolloff, will combine drastically with the phase shift of the crossover. This will result in some rather wonky phase response... it'll make it harder to blend with the subwoofer/woofer driver. Sometimes, it's necessary to steepen (ie, use a higher order lowpass) the woofer crossover, to match the higher slope midbass acoustical total slope (electrical crossover plus box rolloff)... which can then straighten out the frequency response, but at the cost of group delay.

    Point is, it's a matter of NOT wanting to stack up too many orders in the effective filters. Adding in that phase shift (and the associated group delay) isn't optimal in any case...

    Regards,
    Gordon.

  9. #9
    GordonW
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    Whoa.

    Just ran the numbers on the 2012... I'd say, that box is too big!

    One cubic foot gives a sealed box Qtc, of about .3. Now, under no conditions, is it beneficial to have a Qtc of less than .5... because not only do you lose bottom end extension, it also starts to ADD group delay in great proportions.

    Truthfully, in a sealed enclosure, it's HARD to make the box TOO SMALL. If the dang driver will actually FIT in the enclosure, it's NOT too small. I mean, an air volume of .2 cubic feet (or about 5.6 liters), TOTAL, with box fill, would probably do very well... a Qtc of about .90. This will give a "plumped up" lower midrange/upper midbass which can counteract the rising response a bit. Box resonance would be around 270 Hz, which is where I'd put the crossover point. According to my calcs, the driver can handle full acoustic power at about there... a lower crossover in a sealed box, would be displacement-limited anyway.

    If it were me, I'd at least try to make a test enclosure to try a very small volume for the 2012. For one example, a 10" sonotube round enclosure, about 5" deep (internal depth), would be a good one to try. Or, a 9" square (inside dimension) enclosure of about 4 3/4" internal depth. If you don't like it, then try some volumes somewhere in-between where you are now, and this suggested volume here. Somewhere in there, there should be a happy medium...

    If you need the midbass to go lower than this, then I'd suggest a different midbass driver. The hassle of trying to make a ported enclosure mate up with a woofer, using an active crossover, is more than I'd personally want to live with. But, if you did want to try vented, the proposed 8.8 liter enclosure tuned to 93 Hz, is a decent option... it's probably about the most sensible compromise between low port frequency and "propping up" the midbass.

    Regards,
    Gordon.

  10. #10
    Senior Member stevem's Avatar
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    Thanks Gordon, I appreciate your comments. I'm actually trying to increase the output of the driver at the crossover frequency, that's why I want to give the ported box a go. I started with a .5 cu foot sealed box, and enlarged it to 1 cu foot to see if I could get a flatter low end response, but it really didn't do anything. When I run my box program with smaller enclosure sizes, I don't see an increase in the midbass response that you mentioned. Am I doing something wrong? I'm actively crossing over and EQing the HF rise out of the driver as it is. I'm really just trying to avoid boosting the response to flatten the falling resonse at the low end.

    Baron, I feel like I hijacked your thread! Sorry! I hope you're getting something out of this too!

  11. #11
    Member Miss Orchid's Avatar
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    Now, under no conditions, is it beneficial to have a Qtc of less than .5... because not only do you lose bottom end extension, it also starts to ADD group delay in great proportions.

    Truthfully, in a sealed enclosure, it's HARD to make the box TOO SMALL.

    There are JBL systems with Qtc numbers much lower than 0.5 and JBL thought that was beneficial. The readers of this forum are urged to examine group delay figures for sealed systems and vented systems in a variety of box sizes, and in the case of vented systems, a variety of tunings. Sealed boxes can be too small and can decrease power handling capacity due to thermal issues.

    Also of interest might be the use of sealed boxes as two poles of a high pass filter.

    I'm actively crossing over and EQing the HF rise out of the driver as it is. I'm really just trying to avoid boosting the response to flatten the falling resonse at the low end.

    EQ the low end. Possibly a better solution than venting the box depending on the Quality of the EQ.

    The sealed box is providing you with a 12 dB per octave roll off. How many poles in your active high pass filter for the 2012H. What happens when you lower the active portion of the total acoustic roll off.

    When I run my box program with smaller enclosure sizes, I don't see an increase in the midbass response that you mentioned. Am I doing something wrong?

    It's subtle. Read Baron030's second post above. What is the Qts of the 2012H. What is the Vas. Here is the Product sheet for reference - http://www.jblpro.com/pages/pub/components/2012h.pdf

    .

  12. #12
    Senior Member stevem's Avatar
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    Thank you for your reply, Miss Orchid. It appears that I might be going in the wrong direction with ported midrange enclosures, but since the boxes are almost completed, I might as well finish them and see how they sound.



    In answer to your question, I am using 48 db/octave Linkwitz-Riley crossover slopes, which I think are 8 pole? If I understand you, you are suggesting using the 12 db/octave natural roll-off of the sealed enclosure in conjunction with a 36 db/octave (6 pole?) slope for a 48 db/octave acoustical slope. Is this correct?



    I don’t want to use a lot of EQ boost, because the digital crossover/EQ I’m using is running at full scale, and too much boost will make it clip. Global attenuation (in the digital domain) solves this problem, but it doesn’t seem to sound as good.



    By the way, I’m very impressed with your knowledge of things JBL, as well as your command of the English language. You write like someone from the USA, like maybe Ohio? Anyway, thanks again!

  13. #13
    Member Miss Orchid's Avatar
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    It appears that I might be going in the wrong direction with ported midrange enclosures, but since the boxes are almost completed, I might as well finish them and see how they sound.

    Ok. It is good to try things.

    In answer to your question, I am using 48 db/octave Linkwitz-Riley crossover slopes, which I think are 8 pole? If I understand you, you are suggesting using the 12 db/octave natural roll-off of the sealed enclosure in conjunction with a 36 db/octave (6 pole?) slope for a 48 db/octave acoustical slope. Is this correct?

    Perhaps so. Perhaps lowering the active portion of the high pass to the 2012H will help.

    By the way, I’m very impressed with your knowledge of things JBL, as well as your command of the English language. You write like someone from the USA, like maybe Ohio?

    I command many things, how do you say, "grasshopper", including the English language. Know your enemy... And know this - China will crush your capitalist pig country. Oink! Oink! You have become an evil empire and must be stopped. We will buy all your corporations, snatch away all your jobs and smash your economy while you are busy spreading your McDonald's franchises all over the Middle East. Even now we are designing and building your precious JBL speakers.

    Ohio? Ah yes! The place they shoot students who protest. We run over ours with tanks. Isn't that silly girl Katie Holmes from Ohio? Doctorate in Physics and Masters in Mathematics right? Oh wait, my notes are all over the place... she's the scientology major isn't she... yes, we know much about your Ohio...

    Anyway, thanks again!

    My pleasure. Let us know how the 2012H's work out for you.

  14. #14
    BooBoo Magoo
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    First Picture From Mars

    McDonalds is out.
    Walmart's where it's at now Miss Orchid.
    They'll be coming to your neighborhood soon.
    Attached Images Attached Images  

  15. #15
    Alex Lancaster
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    Venerated Miss Orchid:

    I think You may find a life companion (none of that marriage stuff) in Ohio, ask for Mr. Giskard.

    I think running over students and newspeople with tanks was invented in Mexico City in 1968, there might be earlier cases.

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