Infinitely Baffled

Discussion in 'Archived Threads 2001-2004' started by Mike Likens, Feb 27, 2003.

  1. Mike Likens

    Mike Likens Stunt Coordinator

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    I have been reading about IB subs and am intrigued and confused. It sounds like an easy and fun project. I believe I have the ideal placement for one as well.

    I'm thinking of using the area under my stairs. But I have some specific questions maybe someone can help me with. I'm considering the Dayton IB 15" drivers(2) and the PE 250 watt plate amp with remote. How do I wire the 2 woofers to the plate amp? Do I jumper them in parallel or in series? Do these drivers come with dual imput terminals?

    Would dual Tempest be a better driver? Should I be using a stereo amp? Sorry for the simple questions just want to make sure I know what I am doing.

    Also, can the baffle be mounted on the backside of the 2x4s instead of the side closest to the HT room? I am trying to figure out a way to keep 1.5" of MDF from protruding into the room.

    Any suggestions or advice would be greatly appreciated. Thanks is advance.

    Mike
     
  2. ThomasW

    ThomasW Cinematographer

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    HERE's a link for a stairwell IB install. He mounted the baffle as exposed in the listening room. The drivers could be mounted to MDF that is placed behind the drywall. That necessitates cutting 2 circles in the sheetrock.

    There are more examples of wall mounted IB's on the "Cult" gallery pages

    The PE IB drivers are SVC 8 ohm, so parallel the VC's to create a 4 ohm load
     
  3. Rick Guynn

    Rick Guynn Second Unit

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    If you're going to use 2 drivers, I would make a manifold to open into the room. It eliminates some of the mechanical forces and takes less real estate out of the wall itself.

    RG
     
  4. Mike Likens

    Mike Likens Stunt Coordinator

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    Thanks Thomas for the great link and info. That stairwell is exactly like mine.

    Rick: when you say I should build a manifold do you mean an enclosure for the drivers that only opens into the HT room?
    Of course the rear of the drivers will need to be open into the stairwell.

    Also running the drivers in parallel will drop the impedence to 4 ohms thus pulling more power from the amp. It is my understanding that the IB needs less power to operate. Will this configuation overload these drivers? Should I run them in series to maintain an 8 ohm load?

    Thanks.
     
  5. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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  6. Rick Guynn

    Rick Guynn Second Unit

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    Mike, running them in series will give you 16 ohms. If the amp can handle it (which most plate amps can) I'd rather run it at 4 than 8 anyway, as the amp is almost aways going to be rated for more power at that impedance.

    As for the manifold, do something like this:
    [​IMG]

    And yes, IB's generally require less power than a typical sub primarily because of the lack of compression loading. On the other hand, if you have enough power and no runmble filter, they are easier to bottom out too.

    RG
     
  7. Mike Likens

    Mike Likens Stunt Coordinator

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    Thanks for the image Rick. Is there an advantage to this setup as opposed to having the drivers fire directly into the room? Or is this just a cosmetic issue giving you a cleaner look in the HT room?

    I also noticed your manifold is not 14" wide (the width of the insides of the studs). Is there a specific size to this manifold or does this just limit the size of the opening into the room?

    Questions! Questions! I seem to have too many of them.
     
  8. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Yes, there's a definite advantage. With the mounting shown in Rick's post above the woofers move in opposite directions. The manifold box itself must be built sturdy to stand up to the force of the woofers, but otherwise the forces are cancelled by opposing drivers. The wall itself isn't subjected to large forces. If all the drivers fire directly into the room then there is no opportunity to cancel forces. The wall or ceiling now has to stand up to the forces induced by the woofers.

    The Tempests are dual voice coil but the Qts is lower than optimal. So you could use Resistively Damped Operaion to get an Q value between Qts and 2*Qts. The IB15's are single voice coil, 8 ohms and the Qts is just right. So unless you really want the flexibility of RDO I'd just go with the IB15 for ease of use and the cheaper price. Neither has a displacement advantage.

    PE says anything over 150 watts/woofer will overdrive them. So 2 woofers in parallel getting 250 - 270 watts @ 4ohms from a plate amp should be just right.
     
  9. Rick Guynn

    Rick Guynn Second Unit

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    Actually I linked to a picture on Thomas' gallery page. Mine is the same design, I just don't have a picture of it to put up.

    There are two advantages (that I can figure anyway) to this configuration:
    1) Force cancellation. Since the drivers are facing each other in this 'box' structure, all of the forces created by the movements of the cones stay internal to the box, therefore putting very little force/vibration into the interface with the wall.
    2) Cosmetics. Unless you really just want to show off the drivers, there is no actual need to have them facing out into the room directly. It takes up a hack of alot of surface area to put these in a wall that way, and if you ever remove them it's a heck of a lot more repair work. In addition, the baffle/connection area would need additional bracing to handle the forces from the cone motions (see point 1)

    The size of the manifold opening is really not all that important. As long as you don't make it *too* small, you're fine. Making it too small would cause you start hearing noise created by the air moving in and out of it. But you have to get pretty small for that to happen I think.

    If you decide to build an IB, give yourself time to adjust to it. It is a very different (IMO better) quality of bass than you get from almost any 'enclosed' sub. And be prepared to some some adjusting via a parametric EQ depending on where your listening position is (but this is true of any sub).

    RG
     
  10. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Ryan, can you please explain how Resistively Damped Operation works? Does it mean that if you leave open one set of VC's your Qts equals twice the rated Qts of the driver?

    EDIT: This link should be on all of our favorites:

    http://www.geocities.com/f4ier/dvc.htm
     
  11. ThomasW

    ThomasW Cinematographer

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    Here's a LINK to the Adire RDO webpage. It has an excel worksheet for calculation of the "Q"
     
  12. Mike Likens

    Mike Likens Stunt Coordinator

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    Rick - two last questions then i'll stop picking your brain. Is the manifold nailed to the studs or can you have it totally isolated from the wall. I'm thinking I could put 4 legs on the manifold to raise it up then slide it into the precut hole in the drywall. Is this a good option?

    Second - how would you describe the sound of this IB compared to a traditional box? I have never heard one so I have no idea what to expect.

    Thanks for all of the input.
     
  13. Rick Guynn

    Rick Guynn Second Unit

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    Theoretically, you might be able to put it on legs if you do the manifold, as long as you get a good seal at teh wall interface. In practice, I think I would want something a bit more secure.
    I put 2x4's across my joists and attached them to the sides of my manifold. Then I secured the 2x4's to the joists with angle brackets and wood screws.

    The best words I can use to describe the sound of an IB compared to a typical (not the good high-end stuff) is subtle and smooth. It's the way bass *should* sound. Alot of people will actually crank an IB a little louder than it should be because they are so used to the *boom* at certain frequencies.

    BTW, Thomas is the real expert on this stuff. Reading his posts and the posts at his forum is what got me into making my IB.

    RG
     
  14. Mike Likens

    Mike Likens Stunt Coordinator

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    Thanks Rick for your time and advice. I think I am ready to give this thing a try.
     
  15. Jonathan T

    Jonathan T Second Unit

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    What's the advantage of an infinite baffel?
     
  16. Javier_Huerta

    Javier_Huerta Supporting Actor

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    From modelling alone, I can see the advantages are increased efficiency for a given size of amplifier, and a lower delay group than any kind of box (meaning the sound is immediate, without any lags).

    Also, thanks to Thomas advise, I have been able to dial a Qts of around 0.707 with my DVC drivers, so now I'm getting -3 dB anechoic response at 20 Hz with them on an IB. This is getting even more interesting than before [​IMG]

    The major disadvantage I'm looking at right now in my own model is that I need 30 mm P-P excursion at 20 Hz with 280 watts RMS when using 4 12" drivers. When comparing this simulation to 4 ported boxes, cone excursion drops to 6 mm! I hope my speakers can take the beating [​IMG]
     
  17. Jonathan T

    Jonathan T Second Unit

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    Ok guys, thanks. Intresting setup............
     

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