IB concerned?

Discussion in 'Home Theater Projects' started by Demas, Mar 31, 2003.

  1. Demas

    Demas Agent

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    At present i have no subwoofer, but have heard many from the likes of m&k and velodyne and although the quality is very good, many have praised the IB for delivering the finest bass, hence the reason for this.I would like outrageous output, or crazy output as they say, so an IB it has to be then, if only for using multiple very high excursion drivers.I have been accustomed to very high output, and i mean VERY high output at a friends house where he has 4 tumults installed, and it's simply unbelievable the type of output and quality of bass difference one will expect exchanging a box sub to the IB route.Compared to the velodyne HGS18, my friends IB is like looking thru a misty windows and then clearing it to see the whole view, far cleaner and greater detail retrieval.Kick drums are so impressive, and movie effects....well he has 4 tumults so there is little for the imagination.


    Based on what others have attained, my thoughts have headed towards the IB, and using 4 av15's should prove interesting, very interesting.The spl is what i find most intriguing from this combination.ThomasW 12 shivas will achieve greater displacement(guessing around 3-4db) which is impressive and in the crazy output realm, as is Tom Nuisanes 8 15"s IB.When talking about output, 110 db at 20hz is good, 115 is very good, 120 is excellent, 125db is overkill, and 130db+ is crazy, so i would be in the crazy department.Keep in mind that i'm still thinking about doing this, depending on if it's even possible.

    My thoughts conclude that max clean output of 4 av15's with 1200 watts,would reach 134 db at 20hz with room gain.Compared to 4 Tempests, i should be ahead by 10db of clean output.Are these guesses in the right direction?My plans are to build a simple line array, and fit the drivers, powered by the RMX 1450.It sickens me, how easy it is to achieve incredible output and best sound quality(I know it's subjective but experts have praised the quality), for literally small change.A few questions based on my IB.I would be using a closet in another room(about 7m away) and will cut the top of closet ceiling and install the baffle, a simple line array is the most simple of any IB design and is just requires the right length baffel board and cut circles and place the drivers, wire them up and bass nirvana in a nonsarcastic kind of way.This design is the same as Mike Knapps and is dead easy, at least i assume it is, but how much space would be required behind the drivers, as there is very little space in the actual closet, but there is about 14X15X6 behind them where the attic is?Would the IB work with being in another room, only a couple meters away?I'm a little worried that there is very little space in the actual closet, as won't the drivers move too much air inside a small space prove disastraus?Lastly if anyone has an IB, I would be grateful to hear your experiences and insight into your expectations with them.

    Regards
     
  2. Dustin B

    Dustin B Producer

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    I'm a little unclear. You're planning on doing what Mike Knapp did right?

    So you have a closet that will allow the drivers to fire into the room. You also have an attic space that is >1250ft^3. 4 AV15 drivers should have 325ft^3 plus behind them to be a proper IB. So if you seal the closet well and make a large hole in the roof of the closet to the attic you'll have no problems at all. Provided where the drivers will be firing into the room doesn't result in bad room modes.

    PS- Did BrianKR finish his IB and not tell any of us?
     
  3. ThomasW

    ThomasW Cinematographer

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  4. Demas

    Demas Agent

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  5. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Exactly
     
  6. Bryan Michael

    Bryan Michael Supporting Actor

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    dual av15 can push past 125db i was playing brass monkey and turned it up. then turned it down after getting a reading. i need to try lower. also i am in the basement.
     
  7. ThomasW

    ThomasW Cinematographer

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    The stated 7m distance (~21') could create phase issue problems between the mains and the sub. Obviously you should check the potential sub placement, using the methods described on the "Cult" FAQ page, before beginning this project.
     
  8. Demas

    Demas Agent

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    Would 1200watts be overkill with 4 av15's?What amount of power would be needed to reach maximum excursion?

    I just looked at your design, how painful was it to cut the opening to the outlet of your IB to the basement?Do you use a grill to cover?

    I understand that 130db+ at 20hz is impractical in my case, as the drywall will crack and cause falling debris, however I

    would like 121db with the extra 10db+ for greater dynamic headroom, THD levels should be non-existant, and very linear in

    their range.I don't ever won't to worry about bottoming at reference regardless of material, hence the reason of 4

    av15's.Just like your 12 shivas(if you still have them) 18L VD should be capable of greater than 134db at 20hz in a modest

    size room, even though you won't use it, it does contribute to even cleaner output at the required level of use.14L VD

    compared to 18L is about 3-4db, is this more or less correct?Bass cancellations would probably compensate for a couple dbs, how severe are the cancellations?It's just like the B4+, more output than you would care to use,

    yet you benefit with cleaner bass at reference lvl, as the drivers stay in their linear range with less effort.

    Thomas Nuisanes IB with 8 TC-SOUNDS 15"(not entirely sure which driver) is even more crazy, probably more output wise than

    your 12 shivas i'd think, so i'm wondering if his system was more of a design goal of reaching a certain db level, car spl's

    no doubt.My design is line array, which as you know is the easiest to implement, however are there any serious disadvantages

    compared to manafolds?Would I benefit with manafolds in my situation?

    Regards
     
  9. David Lorenzo

    David Lorenzo Stunt Coordinator

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    I modeled your IB plan as a huge sealed enclosure and with 1200 watts you would reach max excursion at ~17 hz.
     
  10. Demas

    Demas Agent

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  11. RichardHOS

    RichardHOS Second Unit

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    From what I can gather, a line array should offer the fewest sonic compromises, but a manifold eliminates most of the mechanical forces produced by the cone motion of the drivers. A wall would probably not take to well to four AV15's mounted directly into it.
     
  12. Mike Knapp

    Mike Knapp Supporting Actor

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    I havent had any problems...

    [​IMG]

    Just a crack or two in the plaster. [​IMG]

    Mike
     
  13. Demas

    Demas Agent

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    If i cannot use a line array, then a manafold might be the only way, and according to other members, this can slightly improve quality compared to line array.

    If this is incorrect, please correct me.I was told over at AVS, that manafolds will give less harmonic distortion if drivers are in opposed directings, but you would get slight bass cancellations as a result.Manafolds would also take care of most of the mechanical forces which another wise would rattle the wall loose and cause cracks, hope this is correct.

    What i would like to know, does it matter how big the manafold is, as i've seen different size manafolds that hold 4 drivers.Ones a small cube, while another is a larger rectangular shape box, so does it affect sound quality if the enclosure is too small, even if it contains the 4 drivers?If this is incorrect, then it seems that i should build a cube that will hold 4 drivers(don't have the proper tools, must go to a carpenter).The only big concern is cabling.How on earth would i get enough cabling from the ceiling back to the listening position?

    Regards
     

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