Twin 1804 IB up and running! Need some BFD suggestions!

Discussion in 'Home Theater Projects' started by Chris Brock, Oct 11, 2004.

  1. Chris Brock

    Chris Brock Second Unit

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    Well on saturday I finally mounted the drivers in their baffle. i went ahead and stuck on some music and began to listen. now Everything you have ever heard about IB bass is 110% true!!!!!!!!!! I literally sat there for about 3 hours listening to different music and movies. There was such a depth, clearity and effortlessness to everything that I kept getting chills in my spine. Let it be known that I am now a converted IB believer and I will never have any boxed sub in my system again. I am going to get everything cleaned up tonight and get some pics up.

    Now on to some questions.................
    I got my first measurements last night. Here is a graph of the correted numbers I got from a Rat Shack meter....

    [​IMG]

    as you can see I have some problems haha! I have two dips at 18hz and 45hz. Below 18hz the response actually climbs again. I was still hitting over 85db at 10hz. I thought I would start out with bringing that big hump between 25 and 35hz down then boosting the dip around 45hz. the one that I am concerned about is that dip at 18hz. I am afraid to really put any boost on that. What do you guys think and does anyone have any suggestions? Thanks a ton!!
     
  2. Seth_L

    Seth_L Screenwriter

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    The BFD won't let you boost frequencies below 20Hz if I recally correctly. It doesn't brickwall at 20Hz, but you can't set a filter with a 18Hz center frequency.

    Did you have your main speakers on when you measured this data?
     
  3. Chris Brock

    Chris Brock Second Unit

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    yes the mains were on and the xover was set at 80hz. I forgot about the BFD not going below 20hz. that kinda rules that one out then. I would like to keep some rise in the area around 20 - 40hz because i think it really helps to add some excitment to movies, but right now it sounds overly exagerated.
     
  4. ThomasW

    ThomasW Cinematographer

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    Hi,

    Glad you're happy with the quality of IB bass ...[​IMG]

    First you don't want to try and boost room induced nulls. Doing that is a physical impossibility. Pull down the peaked frequencies on either side of the nulls, to create the flattest response possible.

    One can boost below 20Hz with the Behringer. It will actually go below 5Hz, but that's only by using a very wide filter centered at 20Hz
     
  5. Chris Brock

    Chris Brock Second Unit

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    ok, so would it make sense then to use some filters in the 20 - 40hz range to bring the response down to around the 90db mark to start with? and also do the same for the frequencies above 45hz? does this at least sound like a start?

    and thomas, Ill get some pics of the installation that you can add to the cult gallery. I would also be very happy to give auditions to anyone interested. what would i need to do to get added to your list on the cult?
     
  6. ThomasW

    ThomasW Cinematographer

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    Yes those cuts are a good place to start.

    Remember that you can fine tune things. Use a wide broadband filter to flatten a big area, Then use a narrow filter inside the same frequency region to boost little dips. Usually ultra flat response isn't needed and frequently sounds a bit dull.

    You can email the pics as attachments to infinitelybaffled at comcast dot net.

    Include an email address for people to contact you and I'll post it to the list on the auditions page
     
  7. Chris Brock

    Chris Brock Second Unit

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    awesome! i will definitly play with the BFD over the next few days and hopefully I can get that curve to look alot nicer. You can also expect to see an email in the next few days with information that you would. Thanks!
     
  8. Seth_L

    Seth_L Screenwriter

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    You might want to try unplugging your main speakers and graphing again. You might find out that the null by 45Hz is from cancellation with your main speakers.
     
  9. BrianAe

    BrianAe Second Unit

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    I've done a lot of reading about IB over the last year and this post finally leads me to ask a question, I hope no one will be offended. For all the reports of the greatness of IB subs, I have noticed the in-room FR graphs of people with IBs in place tend to be all over the place, way worse than most people who post their box sub FR graphs (after proper placement of course). Many people seem to struggle with getting a flat response even after using eq.

    Are IB subs especially hard to integrate? What makes the FR so "bumpy" for so many people? I would think that a FR like the one Chris posted above would negate most if not all of the benefits that an IB would have over a good traditional box sub. Please keep in mind that I greatly admire all of you (including Chris) who take on projects like this. I am not trying to attack you. I merely want to learn more...
     
  10. ThomasW

    ThomasW Cinematographer

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    Not really. If placement is in some obscure place in the room then lower XO points will need to be used

    You maybe seeing more info posted about fine-tuning IB's; since the people that go to the time and trouble to build them tend to really fixate on optimizing the performance.

    IB's are no better or no worse than any other sub when it comes to in-room placement/response.

    Chris' plot doesn't look significantly better or worse than the dozens of box sub plots I've seen people post. His plot basically looks pretty normal for a non-EQ'd sub of any kind.

    Unlike 'portable' subs they can't be moved for optimal placement, that's why all potential IB owners are encouraged to check placement prior to cutting any holes.

    If the proposed placement will work, then the owner is in for a treat given the superior performance an IB provides.

    I realize this info is difficult to comprehend, but IB subs are really in a different league when compared to 'box' designs. And words aren't adequate to the task of describing the differences. Once one has heard an IB sub all other subs (excluding dipoles) are just pretty 'average'.

    In the 4yrs we've had the "cult' forum running, no one has abandoned their IB due to them being unhappy with the performance.
     
  11. Cam McFarland

    Cam McFarland Supporting Actor

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    Why would a dual 1804 IB have such low db levels, or was this just readings at a low volume level? [​IMG]
     
  12. Chris Brock

    Chris Brock Second Unit

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    Cam, yes that graph was at no where near max output. I was simply looking to estabilish a response curve. The only scene that I have actually metered at max output levels is the scene at the begining of FOTR where Sauron's fingers are cut off and he explodes or whatever, haha. During that energy burst the meter read right at 118 - 119db. keep in mind that right now I am still running this off of a single Nady XA900 amp which is only showing each sub somewhere around 300 - 320wrms. [​IMG] So if I go up to around 700wrms per sub (as I have planned) I should be able to get another 3 - 4db out of it. The scary thing was that during that scene even at that level you could hardly see the cones of the drivers moving at all, you had to actually touch them to really know they were even working. amazing!!!
     
  13. Darren_T

    Darren_T Second Unit

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    Glad to hear you are another happy IB convert. I'm in the middle of making the leap myself. I'm trying to decide whether to use four DB PL15D4's or two BP 18's when the new line comes out.

    Did you go through this decision process? If so could you explain what led you to your current decision to go with what I assume is one IB with two 18" drivers.

    Also, sounds like you have great SPL... how big is the room? Is it open to the rest of the house?

    Thanks!
     
  14. Chris Brock

    Chris Brock Second Unit

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    Hey Darren! Thanks for the comments. Actually I originally bought a single 1804 and was intending to use it in a large ported box. While the spl was outstanding the sq just was basically not very good. so I decided to take the plunge and buy a second 1804 and do an IB setup. The room is 19 x 21 x 8 so it is around 3100 - 3200 sq feet. The spl measurement from the LOTR soundtrack was taken right as the amp was begining to clip. Somthing else that was awesome about that scene was the part where sauron's finger hits the ground. when it hits you dont really hear alot of bass but the couch and chairs just shake as though someone hit them from behind. Even my wife kept wanting me to rewind it over and over haha.
     
  15. Darren_T

    Darren_T Second Unit

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    Nice! I just learned that the 1804 is pretty much not an option as they aren't coming back [​IMG] I wonder if four 15" drivers would be similar. I suppose it would.

    I'm still researching etc but have the go ahead from the wife when the right deal on drivers comes along.
     
  16. ThomasW

    ThomasW Cinematographer

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    Not only are the BP1804's gone forever. The DB Drive woofers are disappearing rapidly at the less than $150ea pricing.

    4-15"s will have more displacement than 2-18"s, if the Xmax is similar

    There is a new company starting up that will be offering a new high excursion, high power handling 18". They'll be approx $400ea. Nice thing is that they have licensed Adires' XBL^2 technology. Here are some preliminary T/S parameters for that new 18"

    Fs 16 Hz
    Qms 6.0
    Qes .429
    Qts .40
    Vas 550 Liters
    Re 3.2 ohms
    Znom 4 ohms
    Xmax no less than 27mm one-way
    Sd 1210
     
  17. Darren_T

    Darren_T Second Unit

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    A tad too rich for my blood. I'm trying to stick to $600 and below for the drivers. Sounds like the longer I wait the more screwed I am.

    Where can you find the DB 15" drivers for $150.00? I can only find them for $166.

    Any other sweet deals on drivers on the horizon that you see coming Thomas?
     
  18. Chris Brock

    Chris Brock Second Unit

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    Thomas, has anyone really looked at Resonant Enginering driver or at Digital Designs drivers for IB use? I think they would have some drivers that might have potential. The RE HE series might be a good solution but also a little pricier.
     
  19. ThomasW

    ThomasW Cinematographer

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    Chris,

    I'm sure RE's designs would be fine. I'm not familar with Digital Designs. Do you have a URL?
     

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