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  • badman
    replied
    The distortion reduction from clamshell mounting is not the most effective way- push pull alignments are better. That, however, is offset for a given cab size (again- reasonably well matched drivers within budget is a factor) by allowing twice the SPL for a given amount of cone deflection in the same cab size, which as we all know will substantially reduce distortion for a given SPL. Turning your 12" sub into an effective 18" with force cancellation, even if clamshells were completely ineffective for distortion (which hasn't been my experience though I don't have measurement to back it up) is a pretty big benefit.

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  • Paul K.
    replied
    You said the following, badman, and after I worked through the math more carefully, I determined you are correct:

    "Isobaric creates a 1/2 VAS compound driver, leading to half box size and half efficiency. From there, you can simply consider it a normal driver, and when you add a second one, as with any woofer, you have to double the box size back to the same size required by a single non-compound driver, doubling efficiency back to nominal single-driver specs along with it. There's also the ability to customize the load with your series/parallel wiring configuration to maximize power input which is a nice benefit. To achieve the double output, it takes double the power, not quadruple, and the efficiency is consistent with a single driver in the same box size."

    If box size is all important, an isobaric configuration, whether one uses a single pair of drivers or two pairs, is certainly the way to go as long as driver quality, and therefore performance, aren't unnecessarily sacrificed to get the smaller box. While I can't independently prove it one way or another, claims of reduced distortion appear to be questionable, however.

    Paul

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  • johnk...
    replied
    Originally posted by skatz View Post
    So two drivers would not show lower distortion figures than a single driver at the same level?
    Oh. No. The plots are based on the same excursion so for the same SPL level you would expect lower distortion.The idea of my discussion is not about how distortion varies with SPL but in showing how distortion varies with configuration. How a push pull dual woofer system can reduce even order distortion but the push pull isobaric doesn't have the same cancelation properties.

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  • skatz
    replied
    So two drivers would not show lower distortion figures than a single driver at the same level?

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  • johnk...
    replied
    Originally posted by skatz View Post


    John
    Interesting discussion of these mounting methods and results.
    Couple of questions. How are you seeing the order of the distortion on the graphs you published in this article? Is it a separate vertical line for each order of distortion? Also, how would two drivers conventionally mounted on the same box look in terms of these comparisons?
    The plots show the distortion magnitude at 2, 3, 4, ... up to 10 times the fundamental, thus 2nd, 3rd, 4th..... 1oth order harmonics, left to right. Two INENTICAL drives in the same box would be similar to the first three figures left, right, down one, left . It would not make a difference theoretically if each driver is in a separate box or both drives in a single box of twice the size.

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  • badman
    replied
    Originally posted by Paul K. View Post
    And, you don't think what you said wasn't rude or at least sarcastic:" Always good to look at a link when you don't know what someone's referring to."

    Two drivers in an isobaric configuration and wired in parallel, use twice the power as a single driver to generate the same SPL because there's only one driver facing outward. It would seem to follow, then, that two pairs of two parallel-wired isobaric-configured drivers use 4 times the power to generate twice the SPL of a single driver for the same reason.
    Isobaric creates a 1/2 VAS compound driver, leading to half box size and half efficiency. From there, you can simply consider it a normal driver, and when you add a second one, as with any woofer, you have to double the box size back to the same size required by a single non-compound driver, doubling efficiency back to nominal single-driver specs along with it. There's also the ability to customize the load with your series/parallel wiring configuration to maximize power input which is a nice benefit. To achieve the double output, it takes double the power, not quadruple, and the efficiency is consistent with a single driver in the same box size. Efficiency for a given alignment in normal subs is always tied to box size as you know.

    To have it be 1/4 as efficient, you'd have to be creating some sort of doubly-compounded 4 driver composite with 1/4 the VAS and according box size, one could "string" the drivers I suppose with 4 drivers operating on the same airmass, but that'd be a pretty silly thing do do unless you'd gotten a crazy deal on some super-high vas drivers and could figure out an efficient way to mount them so that the internal space taken by drivers and coupling spaces was minimized. I mentioned a number of times that the benefits were for a given box size, which would preclude describing some sort of 4 driver isobaric.

    The benefits described lead to a higher performance sub within a given box size, which is a key limiting factor for the vast majority of systems. My own ~12 cu ft. 4x12" dual Push-Pull manifold setup is not domestically acceptable for the vast majority of users, but if they wanted the same output, they could achieve it in 6 cu ft. by doubling the number of drivers from 4 to 8, while retaining the force cancellation (but losing some, but not all, of the distortion cancellation. It would be half as efficient. If they had 12 cubic feet to work with, and could swing the cost, 16 drivers would allow them to double the output in the same box size I'm currently using, quadruple power handling, and while distortion cancellation would be less, overall cone displacement would be reduced 50% so distortion would generally be lower overall.

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  • Paul K.
    replied
    And, you don't think what you said wasn't rude or at least sarcastic:" Always good to look at a link when you don't know what someone's referring to."

    Two drivers in an isobaric configuration and wired in parallel, use twice the power as a single driver to generate the same SPL because there's only one driver facing outward. It would seem to follow, then, that two pairs of two parallel-wired isobaric-configured drivers use 4 times the power to generate twice the SPL of a single driver for the same reason.


    Originally posted by badman View Post
    You're being rude, while also being wrong. If you'd read what I'm saying, it's that the 4 drivers in a dual clamshell, in a given box size, are as efficient as the same single driver in the same box, but with higher output, distortion and force cancellation, and more coil to dissipate the heat. Four times the power is required is nonsense. It's the exact same efficiency and sensitivity as a single unit of the same driver in the same box volume. There's a slight adjustment to be made for displaced volume from a second driver in the box, but that's a 1" dimensional change in 1 dimension, in most boxes.

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  • skatz
    replied
    Originally posted by johnk... View Post
    May I suggest to read my analysis and look at the calculated examples here: http://www.musicanddesign.com/Isobaric.html

    John
    Interesting discussion of these mounting methods and results.
    Couple of questions. How are you seeing the order of the distortion on the graphs you published in this article? Is it a separate vertical line for each order of distortion? Also, how would two drivers conventionally mounted on the same box look in terms of these comparisons?

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  • badman
    replied
    Originally posted by Paul K. View Post
    Well, excuuuuse me for making a mistake. My main point are the alleged benefits of isobaric drivers, other than the reduction in Vas and Vb, and you are perpetuating a misleading benefit when stating the kaboominator has 4 times the thermal handling compared to single driver. That actually means 4 times the input power is required with half of it wasted on the 2 drivers not radiating into the room and not generating any SPL. I, too, used an isobaric configuration pair of woofers in each of a pair of 3-way speakers specifically to reduce the required cabinet size, but that was a long time ago.
    Paul


    You're being rude, while also being wrong. If you'd read what I'm saying, it's that the 4 drivers in a dual clamshell, in a given box size, are as efficient as the same single driver in the same box, but with higher output, distortion and force cancellation, and more coil to dissipate the heat. Four times the power is required is nonsense. It's the exact same efficiency and sensitivity as a single unit of the same driver in the same box volume. There's a slight adjustment to be made for displaced volume from a second driver in the box, but that's a 1" dimensional change in 1 dimension, in most boxes.

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  • Paul K.
    replied
    Well, excuuuuse me for making a mistake. My main point are the alleged benefits of isobaric drivers, other than the reduction in Vas and Vb, and you are perpetuating a misleading benefit when stating the kaboominator has 4 times the thermal handling compared to single driver. That actually means 4 times the input power is required with half of it wasted on the 2 drivers not radiating into the room and not generating any SPL. I, too, used an isobaric configuration pair of woofers in each of a pair of 3-way speakers specifically to reduce the required cabinet size, but that was a long time ago.
    Paul

    Originally posted by badman View Post


    Always good to look at a link when you don't know what someone's referring to. 4 drivers, two clamshells in the kaboominator.

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  • 6thplanet
    replied
    Originally posted by jhollander View Post
    Dan Neubecker's Scimitars are push pull in a vented cabinet.
    Same thing I did with my 442's. You get the cancellation of mechanical noises due to the orientation of the woofers, but this is not an isobaric configuration.

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  • skatz
    replied
    +1!

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  • jhollander
    replied
    Originally posted by johnk... View Post
    May I suggest to read my analysis and look at the calculated examples here: http://www.musicanddesign.com/Isobaric.html
    Thanks, I had not seen that before.

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  • badman
    replied
    Originally posted by Paul K. View Post
    I have no knowledge of what the kaboominator is or was, but in any isobaric mounting configuration for a pair of drivers, there cannot be any increase in output SPL since only one driver is exposed to the room. While the thermal handling will be doubled simply due to there being two driven drivers, power requirements are also doubled without any increase in SPL for a specific input voltage compared to a single driver. While distortion may be reduced with the drivers facing each other, the only real advantage is cutting Vas and, therefore, Vb in half.
    Paul


    Always good to look at a link when you don't know what someone's referring to. 4 drivers, two clamshells in the kaboominator.

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  • Paul K.
    replied
    I have no knowledge of what the kaboominator is or was, but in any isobaric mounting configuration for a pair of drivers, there cannot be any increase in output SPL since only one driver is exposed to the room. While the thermal handling will be doubled simply due to there being two driven drivers, power requirements are also doubled without any increase in SPL for a specific input voltage compared to a single driver. While distortion may be reduced with the drivers facing each other, the only real advantage is cutting Vas and, therefore, Vb in half.
    Paul

    Originally posted by badman View Post

    Only clamshell style isobaric reduces distortion, as I mentioned, and that's limited by trapped air compliance (as I mentioned). If you're able to find inexpensive drivers with decent matching and performance, as in the kaboominator, you can have the same efficiency as the single driver, with twice the output, four times the thermal handling, force cancellation, all in the same box size. I'll take that setup over a single higher performance driver anyday.

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