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Thread: port end correction in sub box design

  1. #1
    Senior Member lgvenable's Avatar
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    port end correction in sub box design

    I just want to make sure i've got this down prior to giving my plans to the cabinet maker tomorrow:

    In WinISD; it lists to use port size of 6" and a length (in my case) of 0.467 ft with an end correction of 0.614 (feet again I assume??)

    To make sure, I should then use the longer port length (of 0.614 feet) to achieve the planned tuning frequency, is that correct?

    (& thus prevent the issue pasted into the end of this post.)

    Does the material used have any bearing on the port--> such as using this plastic type port from Martin Sound:



    I also have access to paper spiral wound 6" cores, which have 1/2 inch walls vs the thinner walls of the Martin product. These are basic packaging cores from high speed web handling operation I manage <6" ID and 7" OD>

    From the various posts and articles I have read, it just seems that the port function is to allow air movement from withing and without the box while remaining securely fastened. (& materials of port construction are irrelevant.

    The PVC ports certainly look easier to work with. In the case of the PVC port, does it just need to be pushed into a very tight fitting hole, and then secured with adhesive (or is there a better way to secure the port and prevent movement??)

    Thanks for all the help; I 've probably sounded like a newbie, but I want to make sure I understand EXACTLY what I need to do; before laying down the $$$ and building a box that fails to meet the initial expectations.

    (its implementing the 7P's <proper-prior-planning-prevents-p_ss poor-performance)

    Audioholics Explanation
    As I have read port end-correction is important since the air immediately outside either end of the port acts in sympathy with the design air mass in the port. This has the effect of increasing the apparent length of the port (see image), and hence affects the tuning frequency of the resonator.

    Integra DHC80.1,3x 4636LF, 2360-2446J 2404H,12 x 8340 Surrounds, 2 x4645B, BGW 250D's,250E's,& 750B's 16 amps...7600 watts

  2. #2
    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by lgvenable View Post
    ... 0.467 ft with an end correction of 0.614 ...
    0.467 ft : 0.614 = 0.76 ft is the theoretical length with my understanding, the real horn is shorter as you have mentioned.
    (Others may correct me if WinISD wants to tell something different.)

    BR tubes can make noise which will be diminished by a bigger diameter - 6 inch is just fine - and the ends should be rounded (not meaning the bend).

    The new Everest has rounded ends.
    ____________
    Peter

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