Questions About 4 FI18 IB Setup

[seattle_ice]

I am currently building a home theater and have decided to do an IB with four of the Fi 18" IB subs.

They will be in an array facing towards the seating below the screen. I have a false wall built for the screen, and was planning on building a faceplate that was mechanically isolated from the screen wall. The real walls behind are concrete 12" thick and 9' tall as the theater was built below the 3-car garage.

I am contemplating using the EP2500 for the sub amp.

My question is what would be the best way to run the subs. Should I wire two 2 ohm in series on each channel for a 4ohm load? Or two 4 ohm in parallel for a 2 ohm load? I am not familiar enough with the amps to know what they prefer and/or are capable of.

[hddummy]

I just checked the FI thread for their IBs and they say 500-600 watts for the 18s to hith excursion limits at 20Hz. You'd probably need to do the pair of 4 ohm drivers in parallel and put each channel of the amp into 2ohm load.

[Sonnie]

And then go easy on the gain knob... you will have serious power.

Be sure to take some photo's and keep up posted on your progress. Sounds like it will be a very nice setup.

[Eskimo]

I would do 4-4 ohm drivers, wired series/parallel, and present the amp with a 4 ohm mono load. Each driver should get a little over 400 watts each (real world testing, not manufacturer's specs).

[seattle_ice]

Eskimo wrote:

I would do 4-4 ohm drivers, wired series/parallel, and present the amp with a 4 ohm mono load. Each driver should get a little over 400 watts each (real world testing, not manufacturer's specs).

Why would that be preferable to a mono 2-ohm load? Would that be too much for the subs? Would the amp not handle it as well?

Darryn

[hddummy]

the amp can't do a mono bridged 2ohm. Your options are 4ohm mono brigdged or 2ohm stereo. If you go with the bridged, then you don't need to split the signal and feed it to two channels. If you go with stereo, then you have the option to EQ each channel differently since it is a possibility that the left and right subs may cause different peaks and nulls. I believe the total power output would be the same between the two options.

[seattle_ice]

hddummy wrote:

the amp can't do a mono bridged 2ohm. Your options are 4ohm mono brigdged or 2ohm stereo. If you go with the bridged, then you don't need to split the signal and feed it to two channels. If you go with stereo, then you have the option to EQ each channel differently since it is a possibility that the left and right subs may cause different peaks and nulls. I believe the total power output would be the same between the two options.

Either way, I would use the 4 ohm version of the subs, correct?

If i did stereo, would that mean I would need two EQ units (BFD type) or do they handle seperate channel EQ duties in one unit?

[Otto]

Yeah, if you want a single 4 ohm load, or a pair of 2 ohm loads, you get four 4 ohm drivers.

The BFD will EQ two channels independently at the same time.

[Fi Audio]

Most do the (4)single 4 Ohm versions in a series/parallel combination for a single 4 Ohm load to run mono to the amp (bridged). Seems to be a solid match with 4 of the subs power wise.

Thanks,
Scott

[Saddlesore]

Most do the (4)single 4 Ohm versions in a series/parallel combination for a single 4 Ohm load to run mono to the amp (bridged). Seems to be a solid match with 4 of the subs power wise.

Scott - this is the same wiring that you recommended to me. Does anyone have a diagram of this?

Thanks,
Steve

[Mike P.]

Here you go:

http://www.the12volt.com/caraudio/wo...s.asp~Q~4~I~41

[seattle_ice]

My four subs showed up this morning, so I went ahead and installed them. I wont have them hooked to a source for a couple weeks, but they look great.

Front view:



Back view:

[Mike P.]

They look intimidating, it's definitely going to be worth the wait!

[Owen Bartley]

Darryn, that's a very nice looking setup you have there. Is there a build thread for the theatre and your front speakers? They look familiar, and I want to say Nat P's, but I have a feeling they're not. What are you using for the screen? Can't wait to see how the IB turns out.

[seattle_ice]

Owen Bartley wrote:

Darryn, that's a very nice looking setup you have there. Is there a build thread for the theatre and your front speakers? They look familiar, and I want to say Nat P's, but I have a feeling they're not. What are you using for the screen? Can't wait to see how the IB turns out.

I just started a thread about building my theater
here.

The front speakers are the in-wall versions of the NatalieP's. They are going to be behind my DIY screen using the new acoustically transparent material from SeymourAV.

[jagman]

Looks awesome . I'd put some heavy duty braces running front to back between each sub (so 3 total). That will help hold the quasi manifold/array more steady without restricting air flow.

[seattle_ice]

jagman wrote:

Looks awesome . I'd put some heavy duty braces running front to back between each sub (so 3 total). That will help hold the quasi manifold/array more steady without restricting air flow.

Good idea, that was the plan. I was actually going to brace them all the way back to the concrete wall.

[jagman]

I have a two Avalanche 18" drivers that I've had in an IB but disassembled it due to moving. I am strongly considering selling the two Avalanche's and getting four IB3 18's instead. I love the Ave's, but the new HT is in an open loft (approximately 15k cubic feet), so I need more displacement. When up and running, please talk about your experience. I would appreciate you paying attention to driver excursion with sub 20Hz material. Since you went with four 4 Ohm drivers, you are at risk for bottoming them with loud effects below 20Hz (max excursion occurs at 20 Hz with your wattage when the amp is driven completely). Of course that is theory and often times drivers accept a lot more power than they should theoretically... especially since we rarely drive our amps to nearly clipping. I am contemplating going with four 2 Ohm drivers wired in series for a stereo 4 Ohm load... this gives about 325 watts per driver which means they would hit max excursion at about 9 Hz when the amp is fully driven. Max SPL (above 25Hz) would be decreased by about 4dB, but there would be no risk of bottoming the drivers with the really low stuff so common (yet hard to predict) in today's blockbuster movies. Basically, I'd give up a little max SPL for piece of mind.

[seattle_ice]

jagman wrote:

Since you went with four 4 Ohm drivers, you are at risk for bottoming them with loud effects below 20Hz .... ... this gives about 325 watts per driver which means they would hit max excursion at about 9 Hz when the amp is fully driven. Max SPL (above 25Hz) would be decreased by about 4dB, but there would be no risk of bottoming the drivers with the really low stuff so common (yet hard to predict) in today's blockbuster movies. Basically, I'd give up a little max SPL for piece of mind.

You are somewhat in control of this by simply adjusting the levels going to the amp from your source relative to the rest of the speakers. Or you could set the BFD to roll off the really low frequencies. Or you could swap the 2500 for the 1500. Or run 8 ohm stereo and use 450 wpc for each pair.

I have never believed in having my systems amp-limited. Goes against my grain.

I will let you know how it goes when I get to hooking them up. I just got the projector mounted on the ceiling today.

[Owen Bartley]

seattle_ice wrote:

The front speakers are the in-wall versions of the NatalieP's.

Ah, good to hear I wasn't losing my stuff after not visiting the Shack for a while. ...Just checked the link for your theatre, and wow. What an incredible project, starting from designing and building your own house. Looks like it's going to be a killer theatre, and I can't wait to see it finished.

[seattle_ice]

jagman wrote:

Looks awesome . I'd put some heavy duty braces running front to back between each sub (so 3 total). That will help hold the quasi manifold/array more steady without restricting air flow.

I just finished running the main braces for my subs. I will add a little cross (X) bracing later, maybe after I insulate this whole room.

First I ran some upright braces between each driver:



Then I ran some 2" x 10"s from the back of the brace to the outside wall along the floor. These are nailed and glued with PL400 heavy duty construction adhesive.

I then drilled a 1/2" hole 24" off the floor in 4 locations on the outside wall. After inserting anchor bolts, I used a coupler to attach some lenghs of 1/2" Allthread.



The other end I used some angle pieces I had to fab up some connectors. I lagged those to the LVL beam that holds the wall over the subwoofers and connects to the top of the subwoofer baffle with (2) 3/8" x 2" lag screws each. The other end of the Allthread was then bolted to them and tensioned with a lot of force.



When that step was finished, it looked a little like this:

[jagman]

Wow. Very impressive. That should help a lot .

[Owen Bartley]

Wow... sturdy! That's the kind of beefy overbuilding that I love. Kudos.

[seattle_ice]

Owen Bartley wrote:

Wow... sturdy! That's the kind of beefy overbuilding that I love. Kudos.

Then you will like it now - I added even more bracing in the form of 4" x 6"s next to the Allthread.



So the Allthread is torqued down very tightly, squeezing against the 4" x 6", all of which is holding the lvl beam. I think it is solid.

Here is the overall picture of behind the screen:

[jagman]

I'd have a slide show of your build process you can show on that PJ for those who are interested. That way people who are impressed with your subs will be doubley impressed . Most probably won't care but I'm sure some will.