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  1. #1

    Member Sales Rating: (0)

    Join Date
    Oct 2008

    Default Science behind enclosure volume

    Hello all - yes I'm a newbie seeking enlightment :)

    - I'm interested in designing a special enclosure for a small convertible with no usuable deck behind the rear seat.
    - I'm considering a custom enclosure which straddles the transmission hump in the rear floorboard.
    - I'd like to mount a pair of 6x9 3-way speakers on their long edge, aimed up toward their respective windows (comments on angle?).
    - I'd like to mount an 8" sub-woofer directly over the hump, pointed up and tilted toward the back (comments on angle?).
    - I'm assumming three separate enclosed airspaces, of the recommended volume for each of the three speakers to minimize overall console size.
    - I understand that the recommended enclosure volume includes the volume occupied by the mounted speaker.
    - From looking at the various enclosures on the polk site, it appears that the recommended enclosure volume is (at least somewhat) independent of the overall enclosure shape.

    == Big Question - Help Needed ==
    - I'm looking for the science, the relationship between the enclosure volume and the enclosure shape, because I want to minimize the overall three speaker enclosure size *and* maximize the aesthetics. Perhaps the shapes of the three speaker enclosures can be "interwoven" to meet these objectives?

    - For instance, if I designed an enclosure consisting of a box which is a form fit for a speaker, plus a "dead" soda straw of sufficient length (i.e. additional volume) to meet the overall recommended enclosure volume; would this work?

    - I suspect it would not. I suspect there is also a "minimum straw diameter" related to the maxumum instantaneous air compression due to the cone movement, i.e. a relationship between the rate of cone movement and the rate of air compression for the *entire* recommended enclosure volume such that the cone movement isn't impeded.

    - I'm an EE by trade, and I suspect someone out there has modeled this relationship as some form of series-parallel RLC circuit. That would be great, but any other data (charts, examples, enclosure construction experience, etc) would also be appreciated.

    Michael C

  2. #2
    Polk Customer Service
    Member Sales Rating: (0)

    Join Date
    Jul 2004
    Polk Audio HQ


    Hello, for subs the shape really doesn't matter that much, particularly for sealed subs. Sealed subs also are fairly tolerant to box/enclosure size variations, so you don't have to be dead on the "recommended size." What's more important is that the enclosure is properly braced and rigid enough so it isn't flexing to the beat of your music.

    Where you aim the sub won't matter too much, but they usually work best not firing directly into something.

    For midrange speakers, shape will matter more because the dimensions of the enclosure will start to approach the wavelengths of the midrange frequencies which can result in resonance. And fullrange speakers need to be aimed as best as you can towards the listener's ears.

    Are you planning on running sealed or ported?
    -Polk Audio

  3. #3

    Member Sales Rating: (2)

    Join Date
    Jun 2004
    New England


    You can make the enclosure any shape you want, as long as you can accurately calculate or measure the volume.
    all the best,

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