Should I go back to Ported?

**cdy2179** · **10-06-09, 12:35 PM**

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

**Mike P.** · **10-06-09, 01:42 PM**

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

Quote:

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.

Quote:

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.

**cdy2179** · **10-06-09, 03:56 PM**

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...

**Ryan Anderson** · **10-06-09, 11:10 PM**

Quote:

Mike P. wrote:

Not an ideal solution for a sub designed for IB. IB subs don't model well ported.

just curious what it might look like if they were in a rather large enclosure? It doesn't look like he has a lot of room though...

**cdy2179** · **10-07-09, 08:17 AM**

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????"

**Mike P.** · **10-07-09, 09:35 AM**

Quote:

maybe an LLT built into a stage.....

What would the external dimensions be?

**tcarcio** · **10-07-09, 11:19 AM**

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.

**cdy2179** · **10-07-09, 01:39 PM**

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.

**cdy2179** · **10-07-09, 01:43 PM**

Quote:

Mike P. wrote:

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.

**mikela** · **10-21-09, 07:47 PM**

Did you do measurements before or after installation?

**ironglen** · **10-21-09, 08:01 PM**

Perhaps a 'house curve' is needed?
Add another IB?

I can see the appeal of IB's- figure it out, don't go LLT with those drivers.

**Ryan Anderson** · **10-22-09, 07:34 AM**

Quote:

ironglen wrote:

Perhaps a 'house curve' is needed?
Add another IB?

I can see the appeal of IB's- figure it out, don't go LLT with those drivers.

I didn't care for my WinISD FR curves without room/cabin gain added, I don't know how to do that. How do I simulate room/cabin gain?

**cdy2179** · **11-02-09, 01:53 PM**

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

, 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!

**evilskillit** · **11-02-09, 02:24 PM**

Congradulations to finding a cheap solution to your problem, enjoy your IB sub set up for us

Advertisement