I didn't have to do much, but it was too efficient at around 48hz. Iirc it took about 4db out of there and pushed about 3db into 22hz. To get to what I've found to be close to a half whit down to 20hz (for some reason I didn't tune to a target curve back then, was still quite green lol).I don't find this to be true. At least in my experience... maybe others. I've played with enough IB setups to come to the realization that many aren't really optimized. You really shouldn't have to EQ a proper IB setup into submission much more than a proper sealed setup. A good sealed will dip down just as low and a proper IB should be as musical with decent overshoot, but the difference and the targeted advantage of IB is of course.. better efficiency without the weight and room taken up with an enclosure.
That said... here's some interesting bits of yore. Notice the 12 was only spec'd with a 40hz Fs albeit the 8 & 10 were high 30's? This wasn't uncommon back then though xmax wasn't as high as current subs. Lots of efficiency lost in unnecessary low Fs these days I bet.
Notice #10 in this thread
I see in the search that a lot talk about image dynamics for IB. Name me some good 8" that would work well IB on a rear deck? Also what is the most important specs you folks look at to say this would be a good IB driver?www.diymobileaudio.com
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But what I gained was from 40hz down. I could somewhat tell that it was there previously, but it wasn't balanced with the rest of the response if I wanted leave enough xmax to rock out. Come to find out metal drops will go down into the 20hz range sometimes and the 10in didn't like it at all with higher volumes lol.
But yeah there there is tons of efficiency lost with low FS drivers. But since power is so cheap now, I would rather have a low FS sub with a high xmax and push a bit of boost into the higher frequencies if needed over throwing a ton of boost at the low end of a high fs driver that tends to have less xmax.