1. This is a very informative post! Thanks for sharing your wealth of knowledge.

  2. Excellent job getting this post completed while visiting this weekend! Sorry we couldn’t add more value to the very informative post.

  3. how many cubic ft is the room behind your subs? Also is there a way to connect the lfe channel from my marantz to these amps? Please let me know. New at the diy stuff. Thanks for your time.

    1. Author

      Mark, there are 2 sections to my mechanical room (the room that acts as the enclosure behind the subs.) The total volume is (12ft x 12ft x 10ft) + (12ft x 6ft x 10ft) = 2160 cubic feet. This pretty similar to the volume of my home theater room, which is approximately 2500 cubic feet.

      If you want to get extremely technical about it, look up the VAS specification for the subwoofer, which is measured in Liters. The required volume for each subwoofer should be 10 times the VAS or larger, but there is very little perforce difference if the volume is only 4 times VAS. The VAS of the Fi Audio IB318 is approximately 12.5 cubic feet. So each IB318 needs only about 50 cubic feet minimum; 125 cubic feet for more or more cubic feet to be ideal.

      For my installation of four IB318s, the ideal volume is 500 cubic feet or more, and acceptable performance starts around 200 cubic feet.

      This is a good question; I’ll update the article to include this.

    2. Author

      And to answer your other question, the Behringer EP4000 does have connections for unbalanced inputs on the back panel (in addition to the balanced input connectors.) The connectors are 1/4″ 2-conductor TS style, so you would need something like this 1/4-inch TS to RCA adapter or this dual 1/4-inch TS to RCA cable to connect your receiver to this amp. With these, you can connect the LFE channel of pretty much any receiver to this amp.

  4. I’m very interested in trying an IB set up in my new home theater room in conjunction with my pair of Klipsch KW-120-THX subs. One thing I’ve come to learn is that sub placement can very important based on seating position. You can move a sub 1 foot forward, backwards, left, right or flip it backwards into a corner and get dramatically different base volume from you seating position. With IB set ups your sub placement is extremely fixed and can not be moved or altered to avoid sitting in a completely dead spot in the room. Often you don’t have the option to change seating positions.

    My question is: Is there any way to minimize this chance with different mounting designs say facing the subs straight towards the viewers or doing a manifold where the subs are facing each other?

    My home theater room is in my basement underneath my outside deck. My whole basement is ICF and the back wall of the Theater room that joints into the rest of the basement is an ICF wall as well. The room is very well isolated from the rest of the house. My plan is to turn my front stage into the IB sealed enclosure. Its will be 2′ Deep x 9.5′ Tall x 16′ Wide and was going to run 2 of the FI IB318 in it. That enclosure will easily give me my 10x volume needed and since its not a closet or my attic I wont shake the rest of the house apart or make being anywhere else in the house unbearable while some else is watching a movie. I’m just wondering if I’m best off facing the subs straight out or more of in a dual manifold facing each other inside the enclosure with the opening facing the audience? Like I said earlier this isn’t an enclosure that you can shift around the room to find the best placement.

    Also one other questions. Past experience has always proven that the bigger the sub the sloppier the bass, the smaller the sub tighter the bass. IE 10″ or 12″ vs 18″. Is this still the case with these IB setups say using 4 – 15″ vs 2 – 18″? My 2 Klipsch THX subs sound incredibly tight and I don’t want to turn my Klipsch 9.2 THX Untra2 system into a sloppy mess. Especially after spending all the time to build this custom IB front stage.

    Thanks for your help in advance.


    1. Author

      Hutch, you’re absolutely right about placement greatly affecting response in different parts of the room. This is going to happen regardless of the configuration. The best way to combat this is to spread the subs throughout the room as much as possible, and make sure they are not directly facing one another (creating standing wave reinforcements and cancellations, depending of frequency.) In my opinion, a manifold would tend to focus the sound more than disperse it, so I don’t think this would help.

      There’s always going to be a trade-off for larger speaker cones. Transient response will be slower with bigger cones, but low frequency capability increases. This is somewhat diminished by IB speakers, because the cones are a lot more free-moving compared to sealed enclosures. Having powerful amps and running the speakers well below their highest volume levels will also help. But it’s still a trade-off. I prefer IB for movies, but just the tower speakers and maybe my 15-inch sealed enclosure Velodyne for music.

  5. Carlton,
    I have a question on the Behringer EP4000 Amplifier. As far as I can tell each IB318 is rated for 550W RMS. So, in series that would be 1100W RMS. If the Behringer EP4000 produces 3000W RMS that is almost 3x the rating. Did you have any concerns of overpowering the subs? I am considering the Behringer EP2000 which has a 1300W RMS bridged rating. Any reason you went with the EP4000 over the EP2000?

    1. Author

      Dan, this is a really good point. I went with the 4000 because there wasn’t a huge price difference at the time of purchase. Also, I don’t completely trust power ratings. They seem to be over-inflated and may not be accurate at very low frequencies. In my experience, clipping of the amp output is more likely to cause speaker damage than is over-driving the speaker with too much power. Both are concerns, but I prefer higher power on the amps driving at lower % of total output. Higher amp power also theoretically improves transient response of the speakers, but I can’t say to what extent this is a benefit.

      1. Ok, interesting.
        Via email FI Audio said they actually recommend 600-750W per Subwoofer. Which is different from what I’ve seen online elsewhere (550W).
        How about the Behringer inuke 3000 (or 3000dsp)? They are rated 3000W in to 4 Ohms. A couple places said they have a -3db roll off of 5Hz. And they are more efficient than the EP series. I read on another page that you had a couple of those burn out on you?

        1. Author

          I didn’t have much luck with the Class D amps. I was thinking along the same lines a you: smaller, cooler, more efficient. But not very reliable, and not sure why. My suspicion is that Class D amps derive efficiency from fast switching. But at 5 Hz, the duty cycle is much more demanding than it is at 12k Hz. At low frequencies, the switching spends much more time in the “on” state than the “off” state, leading to overheating. Just a theory. But I can say for certain that conventional amps have been more reliable for me.

          1. How did you mount the speakers to the wood? I assume wood screws, not bolts? What size and length?

          2. Author

            I tried T-nuts and had no luck. There wasn’t enough of a lip a the back of the mounting panel to accommodate them. I had much better success using button-head machine screws inserted from the front), fastened using washers and nylon-insert nuts on the back.

            The only reason to use T-nuts is if you can’t access the back of the sub, as with a sealed enclosure. With an infinite baffle setup, access to the back of the sub typically isn’t an issue.

  6. So how did the IB sub turn out? Does it “work”?

  7. I have had the opposite results with class D amps. For low frequencies, they have been the most reliable and clean sounding. Although the cleanest amp I have ever used for subs in HT was the Adcom 5500. The behringer and other class D amps did not sound as clean (tight bass). My reference movie is the cannonballs firing in the movie Master and Commander. If you don’t have access to one, you don’t know what you’re missing, but they only produce 800 watts total per amp. I had to buy four for each of my 15″ subs at the time. I have a Lab Gruppen knockoff now with 14000 watts playing qty 16 18″ subs. 3hz shakes the whole house! Class D can play low, where the adcom wouldn’t do much of anything. I also felt the LG played cleaner than the Behringers.

    1. Author

      I’ve heard great things about the Lab Gruppen amps. I’ve seen the knock-off versions from China, but ultimately was put-off by the buying process and the intellectual property issues. But definitely a high performance option. Not that I need more amplification; my amps are turned down well below their max power levels already!

  8. Glad I came across this, have been considering as a DIY project for a while. Need to do a lot more research here, but wondered if there was a limit to how large the space behind the subwoofers could be, and whether it needed to be sealed or not.

    I have a very large crawl space behind my theater, also vented to the outside.

    Thanks for the writeup!

  9. I only love you for your subwoofer! (Sincerely, your wife)

  10. Hi Carlton. I have been looking to use an enclosed rack mount cabinet as an enclosure for a subwoofer and learned the IB sub might be the driver to use.

    The audio is used in an open floor plan finished basement with the fronts centers and surrounds in the front quarter of the space. enclosed rack is in a corner cabinet that is approximately 7.5 feet tall and 24″ on each side set in the corner and a flat face to accommodate the 19″ rack. I have 24U’s above and an place below that was supposed to be a door or access panel. I thought this might be a good place for the sub as I do not have many other spaces and do not want free standing speakers. Only problem is that the rack is in the adjacent corner to the back of the room with the screen and surround system. I am worried that the location of the sub being low (1 foot off the ground) and to the right rear of the listening/viewing area. We are talking about 12″ – 15″ behind. Do you think this enclosure or location will present any problems? Also, do you have recommendations for a 15″ or 18″ driver for this scenario?

  11. Do the principles of subwoofer placement apply to an IB setup? I was originally planning to put two JTR Cap2400’s in my theater, one on the front wall, and one in the rear directly across from the other sub. Can I do this same thing with two IB 18″?? I have attic space in both the front and rear of the room. I was thinking I could place them in wall directly across from one another in the front and rear of the room! Thanks!

    1. Author

      Yes, the exact same principles apply to IB subwoofers. If you have the space, ideally, the subs would be located on opposite walls / corners. I didn’t have the space, so all 4 of my subs had to be next to one another.

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