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Discussion Starter #1
About a year ago I put 2 Fi IB18s in a manifold in the ceiling between and slightly to the left of center in relation to my mains in my theater room.
I'm pushing the two Ohm speakers bridged to 4 ohms with a Behringer EP1500.

At first it sounded really bad and after measuring i found a huge spike that went from 20 to 40 hz or so. Very odd. My ceiling was uninsulated because my roof is sprayed with foam.

So I added insulation to the ceiling and put a BFD on the system and put some pretty big notch filters in to level it out.

This made a huge difference and at first it sounded great, but after having it for a while and hearing other subs I feel it never really sounded as clean or powerful as my previous DIY 300watt 15" sonotube sub. Perhaps because of all of the electronic correction.

So now I'm thinking of either putting my spare sub on my seating area and taking the mic around the ceiling to see if I can move the IB to a better spot.
Or maybe build a ported box stage for my 18's and place the stage under the screen and forget IB.

here are some pics for room layout and IB install.
IB located just left of room center.


14x 18' long room seats backs at 14-15' from screen. columns have 5" x 6' long slit ripped out of the middle of the sonotube to let some sound through to the insulation inside the columns, not nearly as effective as corner wedges but using my old sub and the ears they did help. Please excuse the unfinished acoustic panel, the pics were taken several months ago before I completely finished the room.




up in the attic


manifold trimmed out and inside lined with faux black suede left over from columns, flash from camera washed it out in photo


here's the seating position with no EQ


And the nearfield
 

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I'll assume you verified the wiring of the subs and have confirmed each is working properly and they are both working together.

So now I'm thinking of either putting my spare sub on my seating area and taking the mic around the ceiling to see if I can move the IB to a better spot.
That would be my first choice. Your current IB location may very well be in a bad spot in relation to the seating area.

Or maybe build a ported box stage for my 18's
Not an ideal solution for a sub designed for IB. IB subs don't model well ported.
 

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Discussion Starter #3
yea everything's wired properly and they have way more output than I need. I keep the amp turned to about half way as they are surely capable of property and human damage. I guess I should try and find a better spot to move them...
 

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Discussion Starter #5
The room is 14' wide and 18' deep, the only thing I could think of was maybe an LLT built into a stage at the bottom of the screen. In WINISD each Fi IB18 models to a HUGE box, I don't remember how big but it was the size of a small room almost. It was so big I just closed the program and thought "next idea????"
 

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I don't know much about these type of sub setups but could you seperate the subs and place the second in another box ? Maybe speratating them might even out the response.
 

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Discussion Starter #8
No that wouldn't work very well for me. The purpose of installing them in a manifold facing each other is to cancel out mechanical vibrations. Line array designs are similar to what you're suggestiong but that can be very very rough on your wall or ceiling mechanically. That would probably tear my ceiling down and my projector would be blowing lamps every time I turned the sub on.
 

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Discussion Starter #9
What would the external dimensions be?
I don't remember what It modeled out to for internal volume but I could make a stage 12" tall 18" deep and 9 feet wide. I know it modeled out to at least that big for 1 driver, that's why I've passed that idea up. Besides, I sure do like the clean and open look I have now.
 

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Discussion Starter #13
This weekend I dove into my EQ rack... I installed an Emotiva XPA-3 to drive my Rocket 850s and Bigfoot, all I can say is WOW..Great amp!
I also replaced all of my speaker wires from the reciever and amp to the 7.1 wall plate with 14g in-wall and really cleaned it up.
I then moved to the sub, retested with a battery to test wiring...all good!
Then I noticed something.... I power my EP1500 sub amp with a dedicated circuit plugged into an outlet in the attic, I had run the power cable along side my 12g speaker wires feeding the Ib for about 3-4 feet as the cables dropped down behind the EQ rack.

How I missed this is beyond me:huh:, I wired my whole theater paying close attention to avoid this, I guess when I built the IB (after the theater) I was in a hurry and got sloppy.
The 60hz in the electrical line must have been inducing noise that was really muddiying the IB, yet wasn't noticable when the IB wasn't hittin!
 

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You still need a house curve, I don't know how you can stand anywhere close to that much 40-80hz. Start sloping those things @30hz and your room will come alive with crystal clear clarity. Those rockets should give you more than enough 50hz on up, subwoofers have no buisness playing frequencies that woofers can easily reproduce, especially when having even 5db more 50hz can completely kill clarity.
 

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I'd go back if your uncomfortable. Home theater is as much about what you prefer as it is about what the FR curve states.
 

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The problem with a baffle is that you have to find the perfect location before you build (install) it, because obvously you cannot easily move it around and listen and or measure @ the seating position. My guess is if you were to put a box or cylinder sub on the cealing where the baffle is.... you would probably have the exact same problems/issues you have now. I think Xing over lower and steeper would solve most if not all of your problems. If it were me I'd put the sonosub in the center of the rear wall to help flatten the freq responce. Your baffle is basically a duel 18' sonosub in the cealing so adding the sub to the rear and seting the phase ect. correctly should help flatten the responce. Do you have a receiver with audyssey? I do....and until something better comes out I will never have a receiver with out it!! Its without a doubt one of the most important links in the subwoofer chain.
 

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Rich if you have REW then there is no need for Audyssey because REW is a full eq system tailored for the DIY audience.
 

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what???? I do have REW and it is a very usefull tool to get you started eqing and measuring-finding the best location for the sub ect. Its a proven fact that audyssey helps in ways that room treatments can't even completely fix. Now, is it perfect NO, but the diff between on-off compairisons in my room and one of my friends rooms is amazing. If you read the information that is out there about audyssey and the reviews of how it works you'll see how eqing alone is not near enough.
 

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Discussion Starter #20
I think he meant using REW in conjunction with a BFD (Behringer Feed back destroyer) it is more more accurate than Audessey for your sub. I wouldn't reley on Audessey for the sub at all, not only can you not tailor it to your taste but what if you have a null an audessey puts a huge db gain at 30hz and your amp can't handle the gain? And also EQs are NOT at all the same as room treatments. Room treatments such as absorption panels catch the mid to high freq. and keep you from hearing reflections and muddying up your sound... Audessey can in no way accomplish this. It only attempts to eq the sound, but it can't clean up refelections.

Bass traps on the other hand help even out the bass by absorbing low frequencies so they fewer will be free to collide in your room and cause nulls and peaks which is similar to what Audessey does by trying to smooth out these peaks and nulls.
 
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