I have spent far too much money over the years on Hi-fi. Endlessly searching for mere nuances. When if the truth were known most boxes of electronics sound exactly the same.
The IB subwoofer was easily the most serious and clearly audible upgrade in sound quality in nearly five decades of making an unnecessary mess at home.
Rule 1. Use all the same drivers in your IB and get them from a reliable source. Most of my original IB problems were due to being sold crap drivers and my total inexperience with the IB concept. There were no IB Cult FAQs back then.
My first four AE 15" drivers were so far off spec (and cosmetic acceptability) that I am still amazed that the manufacturer had the nerve to remain in business.
All four, straight taper, vinyl coned drivers actually have a measured Fs:32.5Hz instead of the claimed 16Hz. God only knows what the other specs look like in reality! The maker repeatedly denied there was anything wrong with these drivers on the AV forums.
I probably learned far more from my struggle to tame the originals than I might have done had they actually been remotely to the published specs. That does not make me remotely grateful! Why should I be grateful for paying for quality and receiving crap quality drivers?
They (the older 32Hz plastic-coned drivers) only remain in use now because they complement the compromises of the newer drivers and add some free cone acreage. The newer AEIB15 drivers roll off very early and steeply above their peak output with a very narrow, useful power band. Which would normally require a very low crossover point and huge main speakers. While the older drivers roll off very early in the deep bass unless massively boosted low down. I'm talking +16dB @20Hz, two octaves BW of boost from a Behringer DSP1124 Feedback Destroyer! Yet, together, somehow, these very different sets of drivers eventually learned to play together. It took me quite literally ages (years) to get the balance right.
I see the AEIB15 is now being listed again, at twice the original price, after a long hiatus. I wonder what the "real world" TS parameters are this time around? Given that you can buy an 18" from Fi for less money the new AE drivers are not quite the bargain they once were. One 18" Fi IB318 driver moves twice the air of the AEIB15. Making the Fi driver an even better bargain. You can get away with two Fi 18" instead of four AE 15" to make an IB. For the same money you can move huge volumes of air with 4 x IB318s.. You do the maths.
Rule 2: Never (ever) underestimate reaction forces from a row of large drivers in a flimsy structure! Ignore the knuckle-dragging ignoramuses who say a cone has no mass to speak of. They forget the huge mass of air involved and its resistance to violent acceleration and deceleration. Just build an opposed driver manifold first time round and do yourself an enormous personal favour.
Rule 2 (Get-out clause b) If you have a solid concrete or brick screen wall and you can cut holes in that for your drivers then you can safely ignore Rule 2 as well.
Rule 3,4,5-100. Don't think that you can get away without adding LFE for your film enjoyment. Adding a subwoofer to enjoy music is fine. When watching films it is utterly hopeless to just split the Main speaker channels with an active crossover to obtain a bass signal for your IB. I spent years wondering why my IB didn't thunder until I finally added LFE.
If you feel you have any pressing questions on IB subwoofers then consult the Cult of the Infinitely Baffled forum. You could do worse than read the copious FAQs first. Or at least pretend you have before posting:
"[It is] better to be thought a fool than to speak out and remove all doubt."
(A corruption of some fictional, biblical nonsense, usually attributed to plagiarism by Lincoln or Twain)
I think you will find the contents of this blog are ample proof of the above sentiment.
I have my own saying:
"Better a failed clown than a successful bore."
I seem to have spent a lifetime trying to perfect the latter. Imitate me at your own peril!
Keep smiling. Somebody might need one more than you can possibly imagine.