Need Sub Help

Discussion in 'Home Theater Projects' started by Richard=f, Aug 26, 2006.

  1. Richard=f

    Richard=f Auditioning

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    hello, I recently built my own subwoofer, i uses the dayton titanic 15" and of coarse the dayton 1000 watt pate amp. I built the recommended enclosure on the sight, but instead I used two 4" ports at about 33" long each. I used elbows to make it fit, my problem is the driver bottoms out way to soon, I think its the air ressistance. I tryed blocking a port - no difference - then I completly blocked both ports and still almost no diffence. I would think I need too slow down air movment with a baffle or somthing, does anyone else think im right? any suggestions would be greatly appreiciated.

    Thank you.
     
  2. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    I'm sorry but I don't think you're approaching this correctly. If you add some sort of baffle that's significant enough to impede airflow then you're certainly going to affect the tuning and performance of the sub. But how would you predict the effects? Would it really prevent bottoming? Would it give you a peaky frequency response? How would you model it?

    At this point its obvious that you're asking for too much from the sub. Unless there's some flaw in your present enclosure (air leaks? lack of bracing?) that's causing problems, you're going to have to make one of these compromises:
    1) Live with lower output levels
    2) Sacrifice extension to prevent bottoming (apply EQ or redesign box)
    3) Apply more woofers (and amp power) until you can surpass your SPL goals.

    One of the biggest factors here is that your amp is overkill for this woofer. This is not a bad thing but it requires that you be careful with gain and volume levels. A reasonably fool-proof solution can be achieved but it requires planning when selecting components and designing the system:

    Use an amplifier that doesn't have enough power to bottom the woofer in the enclosure. Make sure the amplifier has a good soft-limiting circuit so that it doesn't make offensive noises when it runs out of juice. This solution does not guarantee you'll get "enough output", it just prevents an offensive failure mode. You can take this one step further by using a woofer with a "bottomless" design - it runs out of motor strength before it bottoms.
     
  3. Brent_S

    Brent_S Second Unit

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    According to WinISD, the T15 in 5 ft^3 tuned to 19.38 hz with 1000 watts will exceed excursion from 25 - 40hz. Your minimum Pmax in that range is around 650 watts @ 30hz. If you seal the ports, it gets worse...you drop below a 1000 watts @ 40hz, you're down to 500 watts by 30hz and just over 300 watts by 20hz.

    The good news is it should be seriously loud even with only 600 watts. With 600 watts, you're looking at 111db @ 20hz, 115db @ 30hz, 116db @ 40hz...ground plane. In room, you can easily add 6db or more. Have you checked the volume before bottoming with an SPL meter to make sure it's performing as designed?

    Did you calibrate the sub to your mains? In room, I doubt your mains can produce that kind of SPL. And if they can, you might want to check the OSHA hearing damage charts before indulging too much. :)

    The other possibility is your cabinet has air leaks? Have you checked...use tissue paper or a candle along the seams while pushing it fairly hard. Even small leaks could be causing the driver to unload way before expected.

    -Brent
     
  4. brendy

    brendy Agent

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    Why did you alter the recommened enclosure design? I think that may have alot to do with it.
     
  5. Richard=f

    Richard=f Auditioning

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    hello, first of all i would like to thank everyone for the assistance. These replys see to indicate theres not much that can be done without serious modification and that i can't really afford. A few people suggested that i cound be my enclosure being of poor quality, this I doubt. I sealed the entire enclosure with polyurethan, so no leaks. I'm not sure what i am going to do but testing with an SPL meter would be a good idea.
     
  6. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    I don't consider adding EQ to be a serious or expensive modification. You can get a used BFD for under $100.

    FYI, eliminating box leaks is good, but there's other things to consider too. Like leaks around the woofer gasket and proper bracing.
     
  7. Rocko1290

    Rocko1290 Auditioning

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    I found your problem dude. Are you familar with WinISD? It's an interactive speaker design program. Here is a WinISD graph on which I plotted your project. The problem is you have too much power to the sub.

    [​IMG]

    The red line is 20.5mm (your driver's Xmax). Your driver exceeds it's Xmax at more than 1 point with 1000 watts: about 15.5 hz, 21 hz, and 40 hz. Your problem can be easily solved by getting a smaller amp. I can help you with that if you wish. 350w or 250w would probably be good for that enclosure size and driver, and it will only reach overexcursion (exceed Xmax [bottom out]) at 1 point (which will be in the teens). I wouldn't get anything bigger than a 600w amp for this project. Anything over that, and your driver will overexcurt at about 21 hz & 40 hz as well as about 15 hz. Right now with the 1000w amp, anything under 15.5 Hz or between 20 and 41 will make your driver reach overexcursion. Until you get a smaller amp, there is really nothing you can do about it (unless you want to sacrifice all frequencies under 41 hz). You could just send the 1000w back, and get a less expensive 250w-600w amp. Then it would actually cost you less money.

    Here is the exact same graph, except with 350w of power instead of 1000w:

    [​IMG]

    As you can see, with 350w the driver will only bottom out at about 14.20 Hz.

    Is your enclosure about 180 liters (6.4 ft^3)? If you followed the reccomended ported design on the website, I think it would've been about that size. Also, what was your intended tuning frequency? Two 4" x 33" ports would equal 17.25 Hz in 180 liters. If the values are slightly off, it won't make a difference.

    I'm actually doing a Dayton Titanic 15" project myself right now. My design is 200 liters tuned to 19.21Hz, with a 250w amp (rumble filter @ 17hz). This will only exceed Xmax at 1 point (about 15.5 Hz, which is why I set the rumble filter at 17hz).

    I'd be glad to help you fix your problem.
     

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