Need Help - new IB

Discussion in 'Home Theater Projects' started by ScottDIY, Mar 4, 2005.

  1. ScottDIY

    ScottDIY Agent

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    Just setup an IB using two DPL12. Sounds pretty good. I know that I need a BDF, but I am now wondering if I need to look at some room mod. As I said, it sounds good, but after listening for a couple of hours there is a constant and annoying freq. Almost boomy. I didn't have this with a single sealed unit, any thoughts. Were is a good place to start learning about room modification. ie sound panels and where to locate them.
     
  2. Jason Dalton

    Jason Dalton Stunt Coordinator

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    You really should start with a frequency response plot to see where your trouble frequencies are.
     
  3. Jason Dalton

    Jason Dalton Stunt Coordinator

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    Also, be careful with those DPL12's. I don't know the suspension limits, but you'll probably be able to push them past their linear excursion limits pretty easily.
     
  4. ScottDIY

    ScottDIY Agent

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    driving them with a NAD3150. Might have ~75 watts per driver @ 3.6 ohm.
     
  5. ThomasW

    ThomasW Cinematographer

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    You certainly don't start with room modfications until you have in-room measurements.

    As is recommended, did you test the proposed IB location prior to building it?

    BTW, IB's don't boom. Room geometry and placement of the sub in the room create boom.

    An IB will have more output down low compared to your single sealed driver. That's not boom.........
     
  6. ScottDIY

    ScottDIY Agent

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    well, I didn't mean to be insulting. to me, there seams to be a peak in a freq range and yes I have to locate that freq and watch what mods do to it. But I thought that I could start reading up a little on room mod techniques and see what can be accomplished. I am also looking at som equalization as well. It does certainly go lower, starts droping a little sooner though. The layout, it is coming through an old floor vent that enters two inches from my tv/entertainment system which puts it between my old seald sub and tv.
     
  7. ThomasW

    ThomasW Cinematographer

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    What are the dimensions of the floor vent?

    If the opening in the floor is smaller than a horizontal cross section of the manifold, you've created a bandpass sub. That means there's boost at a specific frequency relative to the size of the opening. It will take EQ to tame it, room treatments won't work.
     
  8. ScottDIY

    ScottDIY Agent

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  9. ThomasW

    ThomasW Cinematographer

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    The opening size is fine, no bandpass issues. There must be a room induced peak.

    Yes the drivers must be wired in phase, otherwise no sound will come out of the manifold.

    Grab a RS SPL meter or better yet use a Behringer ECM-8000, Behringer U802, TrueRTA software, and your PC soundcard.

    Measure the response both nearfield (mic or meter suspended just above the opening) and at the listening position.

    If you use the RS meter create plots using Sonnie Parkers Excel workbook. It has built in corrections for the RS meter. If you go with the mic/software post screen shots of the response.
     
  10. ScottDIY

    ScottDIY Agent

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    OK, Things are looking(sounding) up. I noticed that the box didn't line up properly and tore down the box. I eventually found the addition of the second driver was holding the box from seating in position properly, so I had to do little trimming. Also, since I had it down, I made a gasket out of a sheet of a sheet of packing foam. I am not sure what made the difference, this or just giving it a break in period, but it does sound better. I still have to run some db test and buy an eq. By the way, what is the best way to EQ. I have heard a lot of talk about BDF feedback destroyer. Don’t know the model number. I haven’t had a problem as fare as excursion limits, but does anyone have an idea of power limits for the DPL 12 in an IB?
     
  11. Jason Dalton

    Jason Dalton Stunt Coordinator

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    This is the tool: BFD

    ThomasW pretty much outlined everything you need in his post above, search on the forums about how to go about doing all this testing. Many people have done it before you and lived to tell the tale.[​IMG]
     
  12. Jack Gilvey

    Jack Gilvey Producer

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    Getting rid of room-induced "boom" will require an eq...the BFD is perfect. "Room mods" will have little or no effect at these frequencies, unless you're planning on moving walls.
    In IB, you will reach excursion limits long before you reach "power limits". Pe remains Pe, although it's academic if the driver has already ripped itself apart. You will have to decide if you have enough excursion after you get rid of the room hump, as you're currently calibrated (if at all) to that hump.
     
  13. ScottDIY

    ScottDIY Agent

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    "It’s academic if the driver has already ripped itself apart." Yeah, that's what I'm scared of. How do you know before reaching that limit? I watched the drives through a heavy base piece, I could see it move through some really low sections. Could 70-75 watts/driver drive it to the point of damage?
     
  14. ScottDIY

    ScottDIY Agent

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    Well, for now, it seam to be fine. I think bass is like horsepower, more is always better. I had one DPL already and wanted to experiment with IB. I had other options for two dpl if that didn't work. I am starting to really like IB, so when I move, or atleast move my HT room, I will look a # of 15" or maybe 18". for now, I am just sticking my toes in and testing the water before I jump.

    Oh, the nad has a 20hz rumble filter already. I used to use it when it ran my mains, but not since it's been relocated to sub duty.
     

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