newbie question...........

Discussion in 'Archived Threads 2001-2004' started by Joe Meissner, Apr 2, 2002.

  1. Joe Meissner

    Joe Meissner Stunt Coordinator

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    I have some mdf board laying around and have decided to try and build a sub. I figure i could make this sub 16 inches wide and deep and 24 inches tall. i was thinking a down firing driver (12") with a possible 4" port on the top. Right now i have an old optimus 10" sub and could use the rounded port ends on a new tube for the port and also re-using the 120 watt amp on it too. does this all sound like a good idea? what length tube would i need for say a pe 12" dvc with this size box ? or should i go with a different driver. i want to get some where in the 25hz zone if possible. anything would be better than the 50hz limit on the optimus i have.

    any help would be great

    thanks

    Joe
     
  2. jeff lam

    jeff lam Screenwriter

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    with those dimentions being external, you will have about 2.73 ft^3 internal volume not including braces. The 12 DVC is an excellent driver and it's on sale now at a great price. Not sure how the enclosure volume and driver will match up as I'm not too familliar with the DVC except it's much like the shiva but can use a smaller enclosure.

    The volume seemes a little small for a ported design but you'll have to consult the experts on that.
     
  3. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Without actually running simulations I'd say you could tune to about 23-25Hz in 2.73ft^3.

    Using the port flare from the Optimus may or may not work. Offhand I'd say a DVC tuned to 25Hz with 120 watts might be okay with a 3 inch flared port. That is, the inside diameter of the tube should be 3 inches. The flare diameter will be bigger, of course. A smaller port may have problems with chuffing or compression.

    Since the Optimus sub only claims output down to 50Hz I'd bet there's some sort of built-in filter to protect the woofer from over-excursion at low frequencies. It could start filtering as high as 35 or 40Hz. And all the work you'll do to tune the sub to 25Hz will go right down the drain. You can try the amp, of course. Probably should try it before trusting the opinions of some guy off the internet. But I wouldn't be surprised if the room-shaking bass is filtered out.
     
  4. Joe Meissner

    Joe Meissner Stunt Coordinator

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    the optimus subs amp has volume and crossover controls and the crossover goes down to 40hz. so im not sure that it matters. right now i run the so-called sub at about 60hz on the cross over and volume less than half to keep it from bottoming out. it seems like with a better driver i should be able to turn it up some. so the amp seems ok.? when i watch the pod race scene from star wars it sounds all right but when i push the volume on the amp up it will bottom out in a hurry. its like it is trying to go lower but the driver and box just cant do it.
    what would a sealed sub of that size go down too.? like the one in the link below.
    http://www.jones4.com/jr
    this is a good example of what id like to do as far as size of the sub but want to use a plate amp. but if using a port would get it to go alot lower than i would do that. but if we are looking at say 28hz for sealed and 25-26hz ported than i would just use the sealed design.
    also i would use my exsisting amp to start and then maybe upgrade to the av250 when i got the extra cash. I am trying to do this on a tight budget. so every penny i save is a good thing.
    thanks
    Joe
     
  5. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    2.73ft^3 is way too big for a sealed 12" DVC. The usual recommendation is about 1.2ft^3 stuffed. That should yield an F3 frequency in the low 40's Hz. Ported, you could get an F3 of 25-30Hz (I think) depending on tuning. I don't have the link, but you could do a web search for unibox and you'll find an Excel spreadsheet that will simulate different drivers in different alignments. Its very education to run some simulations.

    So the current sub can bottom, huh? That could mean the amplifier doesn't have a hi-pass filter or that at least its not up at 40Hz. Like I said, its worth a try.
     
  6. Joe Meissner

    Joe Meissner Stunt Coordinator

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    well I think i will try a ported sub. once i finish up remodeling the kitchen i will start making some saw dust. i can build this thing and try it out. if it doesnt work i will just put the opty back together and wait till i can afford a new amp or an svs.[​IMG] a guy can dream cant he?
    thanks for the input
     
  7. Brian Bunge

    Brian Bunge Producer

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    Ryan,
    A 2.73ft^3 sealed enclosure is not too big for a DVC 12! It's all a matter of what type of alignment you're looking for. The 1.2ft^3 enclosure gives you a Qtc around .7, which is probably a good compromise for a sub used for both HT and music. I'm thinking about using the DVC 12's in my 3.4ft^3 sealed enclosures. Heavily stuffed I end up with a Qtc right at .577 which will have superior transient response to the .7 alignment.
    Brian
     
  8. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Yeah, transient response should be better with Q=.577 but I know at least one guy on this board tried a larger volume with poor results. He decreased volume until he found something like 1.2ft^3 worked best. I guess that's just one opinion, but I often see this size (or close) suggested for sealed DVC's over on the PE board and people seem to be very happy with it.

    I've built a 1ft^3 sealed DVC sub and was amazed at its performance. It's a car application, but I did test it out in my huge living room. It probably should be a little bigger than 1ft^3 for home use, but I can't imagine going 170% bigger. Maybe 40 or 60%.

    But really, its all personal taste. Here's an idea - build the 2.73ft^3 sealed DVC and wire the signals from both terminals to a dual-terminal plate on the box. Then you can experiment with different Q's by shorting resistors (or even better - a potentiometer) across one terminal and powering the other. Resistively damped operation.
     
  9. Joe Meissner

    Joe Meissner Stunt Coordinator

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    alright you guys are confusing me now.[​IMG] I didnt realize so much thought and "algebra"?!!! went into designing a sub. I might be better off to wait untill i can afford an hsu, svs or something. I didnt pay attention in algebra class when i was in school (to many years ago) so i just dont get it.!!!!!! oh well thanks for all the help.
    joe
     
  10. Brian Bunge

    Brian Bunge Producer

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    Ryan,

    Agreed that personal taste is the biggest factor. I built a 2ft^3 enclosure for an SV12 (Qtc~.9) for my dad for strict HT use and he loves it! It's not as musical as my SV12's in heavily stuffed 3.4ft^3 sealed enclosures (Qtc~.7) but it will rattle your brain in the 40Hz> area! I could drop the DVC in his 2ft^3 enclosure and it would be more musical but he wants the HT impact of the sub he has.

    Brian
     
  11. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Oh no, please tell me that I haven't turned someone AWAY from DIY! I'll be banned to the hardware section for sure!
    Joe, its really not that hard. Give it a second thought. The unibox spreadsheet I mentioned does virtually all the math for you. You enter the driver parameters and play with box sizes and ports until you get the response you want. Check the driver excursion graph and port velocity graphs along the way to make sure they're reasonable and then you've got your design.
    Here's the link to Unibox:
    http://www.danbbs.dk/~ko/ubmodel.htm
    The parts express 15" DVC driver is on sale today only for $99. This is a great driver and a terrific deal. It can displace about 66% more air than the 12" DVC! You could likely put one of these in a sealed and stuffed 2.73ft^3 and get tons of chest thumping bass. And construction of a sealed box is easier than a ported. Try simulating this in Unibox to see if you like the results. Simulating sealed boxes is super easy! The only things you adjust are input power, box size and amount of stuffing.
    I'm pretty sure this would beat the Hsu for less money (assuming you've got access to tools) and the pride of creation is so much greater than just pride of ownership.
     

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