Infinite Baffle - 2 Fi IB3-18s - Attic Manifold-

I will post lots of pics when I have time, but I now have my infinte baffle sub running.

Equipment List:

Fi Car Audio - IB3-18 2 Ohm Subs - Qty 2
Behringer EP1500 Amp running 2 X 700W @ 2 Ohm
Behringer DSP1124P FBD Parametric EQ
22.5 x 23.5 x 17.5 Box with Inside Dimensions of 19.5 X 22 X 14.5
12 Ga Speaker Wire
RCA to 1/4" phone Cable
Mono 1/4" Female to Dual 1/4" male phone, mono cable.
1/4" phone to 1/4" phone cable

This project came in at $920, but I had some of the materials already and all the tools.

I hit 122db on my RS SPL meter 13 ft from the manifold watching LOTR Chapter 30.

I have not done much RTA yet as I am too busy enjoying it, but some loose measurements had me flat down to 12Hz.

I have very detailed pics at Cult of the Infinitely Baffled.My Project

If you have not heard an IB, you have to. Since there is no box tuned to a certain frequency, it is free to reproduce the most perfect bass you can imagine.

The below is a post from Chrisbee at the Cult of the Infinitely Baffled on my thread, page 7. He explains why not only an IB sounds so good, but how it makes the rest of your speakers sound better as well.


May 13, 2010, 11:30am, pmcneil wrote:No, there is more to it than that. We both had subs taking that load before we built the IB, and my crossover frequency is unchanged.

But maybe the key is not 'taking the workload' but 'good' sub.

I'm wondering what in this case explains the 'good'?

Chrisbee wrote:

The absence of distortion from the IB allows the fundamental to be clearly exposed rather than obscured by false harmonics. No single low frequency tone is ever involved in the reproduction of sound so the false harmonics (of other subwoofers) are as complex as the input signal itself.

The absence of these complex "muddy" upper bass harmonics (from the IB) prevents the speaker's output from being masked. Masking is a very common form of deafness which denies the listener the ability to effortlessly decode the underlying "message" in the signal. Speech quickly becomes unintelligible when masked by background or foreground noise. The brain lacks the ability to automatically filter the wanted signal from the "crud". This makes listening very hard work instead of the natural pastime we take for granted in everyday life.

The IB frees the listener of the heavy computational workload of decoding the hash. Listening becomes easier because it is so effortless to hear the message against the greatly reduced, wideband noise floor reaching our ears.

Despite the subwoofer handling only a couple of lower octaves it affects the entire frequency response of the speaker system. False harmonics combine with other false frequencies to produce yet more complex tones both above and below the original signal.

We learn from birth to recognise sounds and instruments from their harmonic structure. It used to have survival value but now it is mostly for our entertainment, for its emotional stimulus leading to enjoyment.

When denied a true harmonic "signature" to every note the brain becomes confused. It cannot instantly recognise a saxophone from a clarinet or an oboe from a bassoon. The expected harmonic structure is so badly distorted that we waste brain computing time trying to recognise sounds. Like a person learning a new language cannot keep up with fast speech as they have to try and interpret every syllable and inflection into their own, native language. Understanding is easily lost in the race to comprehend meaning by heavy number crunching.

The unwanted and artificial hash produced by most subwoofers has its own frequency response and phase superimposed on the speaker's output. The greater the clarity of the subwoofer the greater the sense of realism because nothing is added which wasn't in the original signal.

If any proof were needed of the IB's greater clarity, realism and low distortion then one only needs to listen to the great pipes of the organ being reproduced.

Where tones are at the limit of audibility (and beyond) the slightest low frequency distortion will rob the listener of the amazing subtlety and clarity of their interplay and means of vocal expression. The way they speak. The leading edge, sustain and decay are all laid bare by the IB. It can play these low notes with breathtaking clarity. Devoid of the masking additions so common to other subwoofers. No two pipes speak alike. Only the IB can reproduce this so effortlessly that we can hear it without overloading the brain's audio analysis into computational reading errors. The pipes become nimble and articulate. Clearly exposing the skills of the organist. Or lack of.

Here are the finished pics from the attic and family room with home theatre.


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I added 2X6s to brace the ceiling joists and to glue and screw the drywall.
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I added camper tape to seal and decouple the box.
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I used plates to secure the box to the joists
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I used banana plugs and cable stay to tie down the cables.
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I built clamps out of 1/8" aluminum and drilled out holes for clamps. I also used bonded washers to seal the hole for the bolt.
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I used rare earth magnets to attach the grill.
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I but back the drywall to place the grill frame and trim.
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A picture of the sub installed.
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Me looking through hole.
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Many thanks to ThomasW at Cult of the Infinitely Baffled. He has step by step instructions how to achieve an IB sub.

I will be EQing my sub soon and posting lots of graphs.

My goal was to extend my low frequency response for HT.

What I got was a sub that sounds different than any sub that I have ever heard. The SQ is through the roof for music and HT. All with cutting a small hole in my ceiling and building the smallest box you can possibly fit two 18s in. I have so much overhead it is not even funny. I have felt quesy watching movies... My ears are still recovering from my demo sessions. Good thing I am on a road trip to give my ears a rest.

Where in the hell are you going to put one or two 5ft x 4ft boxes unless you have a dedicated home theatre or no wife!!!

As far as the drywall... it is relatively easy and very inexpensive to fix if you don't like it. Take the plunge. You won't be dissapointed.

I am assuming penn has heard an IB. I am selling it, but like shoes... no one solution fits everybody. An IB is for some, the DTS-10 is for some, High-end reference subs are for some, and HT in a box is for the rest!!!

Penn-

I am guessing you have heard or own a DTS-10 as well. IYO, how does an IB compare in SQ to the DTS-10.

I am starting to plan my dedicated HT in my basement and the thought of building a massive false wall to house an IB and lose 5ft of room length is getting less and less appealing every day.

You could definitely get away with a smaller amp to save a few bucks. Try mocking the builds up in WinISD to compare.