Builders and acoustics guys

Discussion in 'Amps [BG]' started by basscooker, Dec 18, 2012.


  1. basscooker

    basscooker

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    I was thinking about non-wood materials, composites, and so forth this morning and had a question for you. Is there a reason, other than ease of construction due to use of wood, that cabs are boxes? what made me start thinking in alternate materials was a soda bottle. through design tweaking and the use of sperical space they've managed to "shrink" the 2 liter bottle quite considerably, yet it holds the same VOLUME. could this sort of thinking be applied to cabs?

    in the past three to four years i've spoken with many gentlemen in the "plastics", molding, and fabrication business. no doubt an amazingly expensive venture to get to production. i had a fictional widget prototype quoted $15k. could have been less, or more, but for the size aluminum block to make the mold, $10K minimum, for a prototype. (although if the prototype was right the first time, hundreds of units could be made from it). it seems ridiculous, though, when you consider how much empty space is involved. but there is a manufacturing process called transil wrap. it works in a way like dipping a candle, spinning a potter's wheel and vaccuum sealing, all at once. and the post comes full circle-- do boxes have to be boxes if the TS math works?
     
  2. f64

    f64 Supporting Member

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    The answer is - no, it doesn't have to be a box. This product has been on the market for many years as a low cost auto sub.
     
  3. basscooker

    basscooker

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    thats not a bass cab. ;) how would that cheap sub perform with 600 watts? IIRC bazookas still fart out alot, and they never took over 400 watts. i was thinking about a good way to raise the height without having to compensate with width or depth to keep it stable. and if using alot of "round" in a design would actually work negatively by adding too much boom to be useful FOR BASS GUITAR, thanks for showing me that i have to point this out. on talkbass.
     
  4. wcriley

    wcriley

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    I'm not a builder or acoustics guy, but I would think rounded shapes would result in less phase cancellation inside the enclosure. For the same reason that rooms designed for good acoustic properties don't have parallel walls.

    Maybe something with a "D" shape with the driver(s) mounted on the flat wall?
     
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  6. Bmorefoozler

    Bmorefoozler

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    I know that Greenboy has made mention that a speaker should NOT be in the middle of a box. It is best to shift it up or down and to one side as unequal length reflections are prefferred. A round driver in the middle of a round tube box is about the worst possible configuration as it relates to the in box reflections, from what I can recall beign noted by thsoe smarter then I.
     
  7. qts

    qts

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    very interesting point Bmorefoozler.
    I have search on the web after reading youre reply, because
    I'm planning to build a cab, but want to do it in "the" propper way according the loudspeaker physics.
    I remeber other threads, BogeyBass mention, cab depht is important due quality/performance of the sound.
    I found an interesting thread were he explaines, if I understand to make the cab deep and so avoid (non)centered speaker placement.
    I hope he will chim in

    Here's the link
    http://www.talkbass.com/forum/f15/design-question-speaker-edge-distance-862298/#post12315616
     
  8. fdeck

    fdeck Supporting Member

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    For me, plywood is the ultimate engineering composite. It's cheap, strong, and can be worked using my tools and skills. As you mentioned, molded parts are expensive because of the tooling, but also, most speaker makers don't have the mechanical engineering expertise to design a large molded part. With properly lined cabs, I doubt that the internal shape and symmetry are particularly important.
     
  9. ThisBass

    ThisBass

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    I hope for yourself you understand the meaning of the different amounts of the watts.
    You are talking about 1.8dB difference what is hard to recognize.
     
  10. Mr. Foxen

    Mr. Foxen

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    Box is the most practical shape for space consumption and making it. doesn't need to be, but there's not much upside to funny shapes, you want to steer away for equal or whole proportion lengths, but that is about it.
     
  11. Foz

    Foz

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  12. will33

    will33

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    My take, for what it's worth ........ maybe not all that much:D


    There should be some acoustical advantages to the cylinder, or the sphere/ 1/2 sphere, etc. Standing waves within the enclosure should be less of an issue as there are no parallel surfaces. Higher strength with less material should also be a possibility. A further take on the "arch concept" there. And although you got quoted some pretty high startup costs for such a thing, when you extrapolate it out to some thousands of units, in the mass scale of things, the per unit cost should be a good bit less in the end (assuming you can sell that many:) ).

    Some of tjese plastic molded PA tops you can buy can sound quite good, and are usually either priced a bit less than their wood counterparts...or priced the same, the "added value" being lighter weight. That though, is mostly in the lower end of the "pretty much vocal only", or at least no slamming low frequency end of the market. A small band with a basic PA for themselves to play small bars, or small church installations, or stuff maybe in a college lecture hall that will only amplify speech, etc. When it comes to being sturdy bass cabs, those things would have to be re-worked, beefed up, and you're back to your high startup and needing to sell many units.


    Wood......easy to work with, strong, cheaper production. With regards to shape, the basic cube/box is as high a ratio as you can get in respect to air space on the inside vs. total space occupied on the outside. Round off any corners to get closer to a round shape and you lose internal volume. We need internal volume to make use of speakers that can make bass at any appreciable spl for live music use. Damping and good driver placement can reduce the wave cancellation problem enough to sound plenty good. Also the practical...it's a box...you can set it down and it's stable and you can stack other boxes on top of it. It gets the most for the least amount of packspace.


    I'm all up for new or creative ideas. Have often thought of turning bass drum shells into bass cabs. (quality, well thoight out cabs...not "klops"). But, when it comes to the mass market and value, and moving lots of product, and still sounding good, or good enough to be appealing.....the basic box wins.


    My $.02. I'd be interested in what you have up your sleeve.
     
  13. bassman314

    bassman314 I seem to be a verb, an evolutionary process... Gold Supporting Member

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  14. qts

    qts

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    Therefore I wonder. why all the cab builders never talk about shape or ratio's.
    It seems like it's not that important,.or is there a rule of thumb like speaker height + some inches =......
     
  15. Foz

    Foz

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    Shape does matter... a sphere has a single chain of harmonic resonances and this aint a good thing... also you lose baffle reinforcement [but you also lose baffle step]. Also the aforemention impracticality of sphere and tube shapes. Still these shapes have been effectively used = just like every other "out there" speaker topic this one comes down to compromises.

    Here's a commercial application of a tube sub

    [​IMG]

    http://www.diyaudio.com/forums/subwoofers/203590-narrow-space-tube-sub.html

    We did something similar at the farm... That's a 21" 1k watt Beyma woofer

    [​IMG]

    [​IMG]
     

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