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Thread: SUB18 Clone

  1. #16
    Senior Member Ian Mackenzie's Avatar
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    Where are the ports located? Don't locate a port closerthan one diameter to a side or rear wall.


    In Bassbox 5.1 (a professional program) the length for 2 x 4 inch ports is 8.4 inch (no fibre glass lined walls) Fb 25 hertz

    With fibre glass lined walls and box internal dimensions that equate to 9.00 cu ft3 after subtracting bracing and any other solid objects port length is 7.20 inches x 2 4 inch port Fb 25 hertz

  2. #17
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    It looks, more or less, like a SUB18 with the ports equally spaced between the driver and the corner of the box.

    So BBP is claiming 7.2" (the box is fiberglass lined on 5 sides). Below is what the precision port claims. Note we cut the ports for 24Hz so we could shorten as needed based on the as-measured. I wonder why there is a difference. You'd think that Precision Port would know their own port. Then again, as you can see, the on-line program claims that one takes the value and subtract 6" for everything but a 2" port but the included sheet claims to cut it back 5".
    Attachment 80414

    Then again, I'm willing to roll with the current tuning and use a B6 alignment. It looks like it would be pretty flat down to 18Hz.
    Attached Images Attached Images  

  3. #18
    Senior Member Ian Mackenzie's Avatar
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    But your port is flared

    I would go my real motion of the driver.

    Adjust 1/2 inch at a time until you get the correct tuning.

    You know JBL empirically tunes their systems.

    The impedance null is not accuracy due to inductance of the driver.

    B6 done right is a smaller box and is not that easy to get right.

  4. #19
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    Driver motion agrees with the meter (I had a series resistor in line with the amp and the meter directly on the driver) but I also verified with actual driver motion and port air velocity. A friend that has BBP 6 ran the numbers I measured and came up with an attractive B6 tuning response.

    Next I'm going to measure the response of what I have and if I like it, I'll make another to match.

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