There are different ways to achieve what you want.
An IB is a superb way to achieve bottom octave extension, with low power/low compression, with a nice subjective sense of bass quickness or "speed". Due to four 18's covering the duties, the driver movement is minimized to a significant degree, thus minimizing overshoot and other non-linearities and distortions that may accompany a small diameter sealed approach, pushed to it's excursion limits.
Excursion headroom, and low power levels,....these are significant benefits of the IB approach.
The subjective kick in the chest feeling, can be related to many things, chiefly a large amount of SPL@a given chest resonance. Oftentimes this is elicited from highly capable and well optimized mains, that are ideally mated to a subwoofer system of any type. Phase coherence/integrity in the octave spanning 60-180hz (both sub and mains) will contribute strongly to this "punch" effect. Additionally, and perhaps most importantly, ample bass trapping, and a well optimized time domain absent of significant ringing contributes highly to a clean punchy response, with a high degree of perceived "speed", due to cleaning up the room overhang energy.
*Four IB3-18's, w/an EP4000 (total around $1200-$1300) will yield ~125db@1m@20hz.
That's with only about 200 watts per driver, so compression effects are virtually non-existent.
Yes, you should attempt to assure no big issues with your IB placement, however if your location isn't perfect you do have some tools at your disposal. I just posted such a thing a short time ago at The Cult;
"However being as limited to manifold location options, I'm approaching it with my eye on the end goal. The primary IB manifold location, is but one step in the entire process. Mitigating potential response issues with another manifold, and/or small sealed balancing subs, all combined with significant bass trapping etc., will be my approach.
I'm so limited with attic height, my manifold(s) must reside along a general line running front to back through the room. Knowing the need to psycho-acoustically link the upper octaves of a subwoofer system's coverage to the bottom octaves of the mains coverage, manifold placement and proximity to the mains is key. All said, everything points to a manifold in the display/mains end of the space,...front left corner, regardless what issues arise. Clearly, a multiple location subwoofer system solves many issues encountered in small room acoustics. So whether I build a four 18" driver manifold, a mammoth 8 driver IB, or two 4 driver IB's, all indications point to my room needing additional subs, perhaps small sealed, to further smooth the response and lower distortion at any given operating level. So build the front left manifold, measure the resultant outcome, and proceed from there with filling in the nulls, and smoothing the peaks with the tools and approach I listed above."
Flat, Deep, Clean, Linear, and Loud
Active 16.8kw, 7.3 system
(3)Seaton Cat12C up front, (4)QSC K8 sides/rears
(2)Seaton SubM-HP, (4)18" IB