Would this sub idea work?

Discussion in 'Archived Threads 2001-2004' started by Lee Weiss, Apr 4, 2002.

  1. Lee Weiss

    Lee Weiss Stunt Coordinator

    Joined:
    Mar 5, 2002
    Messages:
    73
    Likes Received:
    0
    Trophy Points:
    0
    I just received my Dayton DVC 12" sub and PE 250w amp. I have plans to build a small sub due to size constraints, and was thinking about a 1.2 cu ft sealed.

    I really like the idea of IB in my attic, but don't have the money or need for something so earthshaking.

    I would also prefer a larger ported box so it can go lower, as I want this mainly for HT.

    My idea is to build a vented box, about 3 cu ft (depending on what would be best suited for HT and the driver) and to mount it up in my attic above my mains and have the woofer vent down into the room like an IB.

    Is this stupid, would this work? This would give me the size box I would prefer without taking up living room space.

    Thoughts, ideas, comments?
     
  2. Brian Bunge

    Brian Bunge Producer

    Joined:
    Sep 11, 2000
    Messages:
    3,716
    Likes Received:
    0
    Trophy Points:
    0
    Lee,

    An IB would actually be cheaper than the ported enclosure. For an IB all you would need is a board to mount the driver to and just have some sort of opening into the room. You could still use your plate amp without any trouble.

    Brian
     
  3. Rick Guynn

    Rick Guynn Second Unit

    Joined:
    Mar 23, 1999
    Messages:
    473
    Likes Received:
    0
    Trophy Points:
    0
    Why not just do a single-driver IB? I don't think IB's have to be multi-driver, they are just more effective that way. I am sure ThomasW could give a better opinion on this, though.
     
  4. Lee Weiss

    Lee Weiss Stunt Coordinator

    Joined:
    Mar 5, 2002
    Messages:
    73
    Likes Received:
    0
    Trophy Points:
    0
    Brian,

    The problem, if it is one, is that I only have one woofer and an attic that spans the length of the house. About 35' long, about 4' high in the center and sloping down to the soffits. It is a low-pitch roof. I thought there had to be some correlation between the size of the woofer and the enclosure it is in.

    I could just mount the woofer on a plate, secured between the joists and point the woofer down. I think it would actually look pretty cool.

    If you care to elaborate, I am all ears.
     
  5. Dustin B

    Dustin B Producer

    Joined:
    Mar 10, 2001
    Messages:
    3,126
    Likes Received:
    0
    Trophy Points:
    0
    To be effective an IB is supposed to completely isolate the front wave from the back wave. Ie the air at the back of the driver should have no way to interact with the air form the front of the driver. Next is the amount of air in the back of the driver needs to be at least 4x the Vas of the driver. Preferably 10x or more. As should the amount of air in front of the driver.
    Another thing you could do is build a manifold big enough for 4 drivers. Start with one (sealing off the holes for the other 3 drivers), and just keep adding to it as you get more money. Although with a manifold mount it would be best to do two drivers at a time.
    Here is what is meant by a manifold:
    http://home.tampabay.rr.com/kraushome/IB.html
     
  6. Rick Guynn

    Rick Guynn Second Unit

    Joined:
    Mar 23, 1999
    Messages:
    473
    Likes Received:
    0
    Trophy Points:
    0
    Lee, as Dustin said, the volume of the enclosure is recommended to be a minimum of a multiple of the Vas. You can't have 'too big' of an enclosure for an IB. I believe the the whole idea behind the IB concept is to eliminate the effect of the air pressure dynamics from the functioning of the driver, thus rendering the Qtc to be the Qts of the driver (I think that's right).
     
  7. Lee Weiss

    Lee Weiss Stunt Coordinator

    Joined:
    Mar 5, 2002
    Messages:
    73
    Likes Received:
    0
    Trophy Points:
    0
    Dustin,

    I had actually looked at that link earlier this morning and that is what interested me, although I had thought about it before.

    I think the driver I bought has a Vas of 4.25, so the volume of my attic space is easily 10x that. I understand the concept of separating the front and back. Is there any formula for making the manifold? I might be concerned with drywall rattle, would that be something to worry about?

    Lastly, what makes the IB a better bet than an a vented or sealed box?
     
  8. ThomasW

    ThomasW Cinematographer

    Joined:
    Nov 6, 1999
    Messages:
    2,282
    Likes Received:
    0
    Trophy Points:
    0
     
  9. Lee Weiss

    Lee Weiss Stunt Coordinator

    Joined:
    Mar 5, 2002
    Messages:
    73
    Likes Received:
    0
    Trophy Points:
    0
    With this kind of setup, what kind of things in my house would be sharking and vibrating that might not with a box?
    I like the idea and my build both a box and the IB to see what the difference is. Problem is, I just got served with jury duty in the middle of my two week vacation [​IMG]
     
  10. Lee Weiss

    Lee Weiss Stunt Coordinator

    Joined:
    Mar 5, 2002
    Messages:
    73
    Likes Received:
    0
    Trophy Points:
    0
    Last question before I build...
    I am concerned with two things.
    Will the sound from the IB resonate throughout the other rooms below the attic? I cannot have that with a newborn.
    Will the drywall on the ceiling suffer from vibration enough to pop the nails out?
    Is it possible to isolate the manifold from vibration like the do when they earthquake-proof buildings?
    If this would not work, I am limited to a small sealed sub, and that is not really what I want. And I want to build it yesterday [​IMG]
     
  11. Brian Bunge

    Brian Bunge Producer

    Joined:
    Sep 11, 2000
    Messages:
    3,716
    Likes Received:
    0
    Trophy Points:
    0
    Lee,
    Yes, the sound will resonate throughout the house. But then again, my dual sealed subs do too!
    It's possible to have nail pops if the sub excites the walls enough, regardless of the application used (IB, sealed, ported, etc.).
    I believe Thomas uses foam in between the mouth of the manifold and the floor joists.
    Brian
    P.S. That was actually 3 questions! [​IMG]
     
  12. JerryD

    JerryD Extra

    Joined:
    May 15, 2000
    Messages:
    24
    Likes Received:
    0
    Trophy Points:
    0
    There is at least one other factor to consider if you are doing an IB with just one driver. In an IB, there is not as strong of an "air spring" behind the driver to help limit its travel as there is in a sealed or vented design. The result is that any given driver will tend to run out of travel (hit Xmax) at a lower power level in an IB than it will in a normal box. You can use most any of the box simulator programs to determine at what point this will happen by simulating a sealed box with a volume of 4X or more of the Vas.

    I have an IB with two of the PartsExpress 15" DVC drivers. I have yet to bottom it out with any level my ears will tollerate. I power it with a single PE 300-794 plate amp.

    One thing unusual about my IB is that it is mounted in the riser box that I use to elevate two levels of the seating in my HT. The reason I chose this over using the adjacent storage room is that it does not send as much bass all over the house. I guess one other benefit is that the bass is more tactile because it shakes the floor under the couch more.
     
  13. Lee Weiss

    Lee Weiss Stunt Coordinator

    Joined:
    Mar 5, 2002
    Messages:
    73
    Likes Received:
    0
    Trophy Points:
    0
    Brian,
    I mostly concerned that my wife would be laying in bed and could hear bass above the bed. I guess I won't know until I try it.
    I was more concerned of an IB popping nails because of it actually touching the drywall in the ceiling, but I guess it really does not have to.
    In terms of foam between the manifold, I will have to look again at the Mini-me. I was thinking of some elaborate engineering project, but I guess foam would work too.[​IMG]
    I don't think I could understand or appreciate the differences between enclosures unless I tested them. I think I am going to waste some MDF and build one of each and learn a little.
    Thanks for all the input. I will post pics when I finish.
     
  14. Brian Bunge

    Brian Bunge Producer

    Joined:
    Sep 11, 2000
    Messages:
    3,716
    Likes Received:
    0
    Trophy Points:
    0
    Lee,

    I have a rather small 1700-1800 sq.ft. house that is and open floorplan and built on a concrete slab. If I'm watching a movie and my wife is in bed she can most definitely hear my dual sealed subs. Bass will travel throughout your house rather easily unless you can build a dedicated room that's sealed off from the rest of the house and heavily insulated.

    I, along with everyone else, look forward to pictures!

    Brian
     
  15. Lee Weiss

    Lee Weiss Stunt Coordinator

    Joined:
    Mar 5, 2002
    Messages:
    73
    Likes Received:
    0
    Trophy Points:
    0
    I am in the midst of building my IB box. I decided on a box big enough for only two woofers.
    The Jasper circle jig is worth it's weight in gold. Just got to play with it for a few seconds. Got a $99 Ryobi plunge router since I have not gotten my PC fixed yet. Pretty darn nice for the price and worth it for the casual router user.
    This may be a dumb question, but I am making the manifold center above the mains. My ultimate idea would be a suspended manifold that does not mount rigidly to the joists. Is that overkill?
    Wish I could get out there now and finish but no lights in my dinky shed [​IMG]
     

Share This Page